Vulcan Alaska

vulcan alaska edition

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vulcan alaska edition

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VULCAN is curated and edited by Maketa Mabane with content provided by Alaska Volcano Observatory (AVO) and United States Geological Services.

A special thanks to Steve McNutt & Cyrus Reed for authorizing the use of the text and pictures from Alaska Volcano Observatory.

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akutan peak

elevation: 4275 ft latitude: 54.13308째 N longitude:165.98555째 W

Akutan is one of the most volcanically active islands in the eastern Aleutian arc.

official name: Akutan Peak type: Stratovolcano latest activity: 12.18.1992

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ty p e :

AKUTAN VOLCANO IS a composite stratovolcano with a circular summit caldera about 2 km across and 60 to 365 m deep(Byers and Barth, 1953; Romick and others, 1990; Motyka and others, 1981) and an active intracaldera cinder cone.

The caldera rim reaches a maximum altitude of 1303 m at Akutan Peak, the remnant of a pre-caldera cone now filled with a lava plug. The caldera is breached to the north. Caldera subsidence accompanied or followed eruptions from a series of rim vents. The vestige of a larger caldera, of probable late Pleistocene age and at least in part older than the cone of Akutan Peak, extends 1.5 km southwest of Akutan Peak and is terminated to the north by the younger caldera. Small glaciers fill the older crater and lie within the southwest and southeast margins of the younger caldera.

“The active intracaldera cinder cone is over 200 m high, about 1 km in diameter, and located in the northeast quarter of the caldera. Three small sulfur-lined craters occupy its summit and several fumarole zones are present along its south and southwest flank

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DEFINITIONS

Stratovolcano A stratovolcano is a tall, conical volcano composed of one layer of hardened lava, tephra, and volcanic ash. These volcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava that flows from them is highly viscous, and cools and hardens before spreading very far. The source magma of this rock is classified as acidic, or high in silica to intermediate (rhyolite, dacite, or andesite. or basalt).Many stratovolcanoes exceed a height of 2500 m.

Caldera A caldera is a large, usually circular depression at the summit of a volcano formed when magma is withdrawn or erupted from a shallow underground magma reservoir. The removal of large volumes of magma may result in loss of structural support for the overlying rock, thereby leading to collapse of the ground and formation of a large depression.

Calderas are different from craters, which are smaller, circular depressions created primarily by explosive excavation of rock during eruptions.

Pleistocene Age The most recent episode of glaciation, the Pleistocene epoch, is commonly referred to as the Ice Age and began approximately 1.6 million years ago. During that time there were a number of advances and retreats of the glaciers, which are termed glacial and interglacial stages, respectively. The glaciers of Greenland and Antarctica are remnants of the last glacial advance.

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The lava flows and pyroclastic deposits of Akutan volcano are no older than

Pleistocene as Romick and others (1990) report ages of 1.1 +/- 0.1 to 1.8 +/- 0.8 Ma for the oldest of these rocks. The caldera-forming eruption occurred about 5,200 yBP and was the source of small volume andesitic pyroclastic-flow deposits in valleys on the north, south, and east sides of the volcano. Young basaltic lava flows, some of which were erupted in 1929, cover the caldera floor south and north of the cinder cone and extend several hundred m downslope through the crater rim gap.

Flows extruded in 1947 blanket the central portion of the northwest end of the island at Lava Point, where about 4 square kilometers of jagged aa basalt occurs adjacent to several cinder cones. The entire island is mantled by an ash layer that thickens toward Akutan Peak; landslide and mud flow deposits . have concentrated this ejecta in the valleys north and northeast of the caldera and a maximum fill depth of 7 m occurs at Wooly Cove.

Recent eruptions produced only small amounts of fine volcanic ash that fell primarily on the upper flanks of the volcano. Small amounts of ash fell on the Akutan Harbor area during eruptions in 1911, 1948, 1987, and 1989. Plumes of volcanic ash are the primary hazard associated with eruptions of Akutan Volcano and are a major hazard to all aircraft using the airfield at Dutch Harbor or approaching.

Akutan Island. Eruptions similar to historical Akutan eruptions should be anticipated in the future. Although unlikely, eruptions larger than those of historical 10

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time could generate significant amounts of volcanic ash, fallout, pyroclastic flows, and lahars that would be hazardous to life and property on all sectors of the volcano and other parts of the island, but especially in the major valleys that head on the volcano flanks. During a large eruption, an ash cloud could be produced that may be hazardous to aircraft using the airfield at Cold Bay and the airspace downwind from the volcano. In the event of a large eruption, volcanic ash fallout could be relatively thick over parts of Akutan Island and volcanic bombs could strike areas more than 10 kilometers from the volcano.

A lava flow in 1978 traveled through a narrow breach in the north caldera rim to within 2 km of the coast. A small lake occupies part of the caldera floor. Two volcanic centers are located on the NW flank: Lava Peak is of Pleistocene age; and, a cinder cone lower on the flank which produced a lava flow in 1852 that extended the shoreline of the island and forms Lava Point. An older, mostly buried caldera seems to have formed in Pleistocene or Holocene time, while the current caldera formed in a VEI-5 eruption c. 340 AD. The volcano erupted most recently in 1992, but there is still fumarolic activity at the base of Lava Point and there are hot springs North-East of the caldera.

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eruptions and activity

1996 Earthquakes Intense seismicity was felt by Akutan residents on the evening of 10-11 March 1996. The swarm of 80 earthquakes lasted for 11 hours. The largest earthquake was magnitude 5.1. On 13th March, felt-earthquakes began occurring at a rate of greater than 1/ minute. The largest earthquakes were felt as far away as Dutch Harbor/Unalaska 50 km SW of Akutan. On 14th March, earthquakes were strong enough to ring the bell in the Russian Orthodox Church, during a second swarm of 120 earthquakes. In total, more than 3000 earthquakes occurred beneath the island. Extensive ground cracking resulted, but no eruption occurred.

1992 Eruptions Small steam and ash eruption occurred at Akutan volcano in April and December 1992.

1991 Eruptions Summit ash emissions began in September, with a plume to 4500 m altitude. Ashfall was reporded at Akutan village.

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1990 Eruptions Small ash eruptions were reported in September and October.

Heights of plumes were 1500 m above the summit.

1989 Eruptions In March 1989 an air shock wave was felt by a pilot flying over the western shore of Akutan.

1988 Eruptions Ash emissions occurred at Akutan volcano between March and June 1988. Most observations were by pilots.

1987 Eruptions On 22nd June 1987 a summit glow was seen by a fisherman in the Bering Sea. Two days later, a pilot reported ash emissions to 1300 m altitude from a large cinder cone in the summit crater.

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1986 Eruptions In June, numerous ash emissions to an altitude of 3.5 km were visible from Akutan village.

1980 Eruptions On the 3rd July a recent lava flow that had moved through a breach in the NW caldera wall was observed.

1978 Eruption In 1978 lava flowed through a gap in the caldera and came within 1 km of the sea in the north. Strombolian eruptions occurred at the summit.

1977 Eruptions Eruptions began in May, with light brown ash emissions every 15 minutes. Incandescence was noted in some eruptions.

1974 Eruptions In February, ash was emitted hundreds of feet into the air, and lava flowed down the flank.

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Other Eruptions

1912 1911 1908

1973 Eruptions

1907

Akutan volcano erupted ash and steam for several months, with

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the mountain snow-free.

1892 1887

1946-48 Eruptions

1883

Lava flows occurred at the volcano caldera.

1867 1865 1852

1924 Eruption

1848

A lava flow occurred on the floor of the caldera.

1845 1838

Eruptions in the 1850’s A cinder cone and two lava flows were erupted north of Lava Peak. The lava flows formed two lobes which flowed into the sea, forming Lava Point.

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culture Akutan Peak

AKUTAN IS A WONDERFUL destination for ecotourism. Hiking on the island is diverse wildflowers and berries abound on the hills and mountains. There is a thermal hot springs within hiking distance of the village. Hardy souls have climbed all the way to the crater of Akutan volcano, which is about seven miles west of the village. The volcano is active, with steady steam emissions and an occasional dusting of volcanic ash. There are no bears on the island, although you can see an occasional fox, and Akutan and the surrounding islands teem with birds and sea life. The whiskered auklet is found on the nearby Baby Islands, one of only two places it exists in the world. Fishing is excellent in the waters around Akutan, and some of the largest halibut in the world have been caught in Akutan Pass at the west side of the Island.

Akutan is located on Akutan Island in the eastern Aleutians, one of the Krenitzin Islands of the Fox Island group. It is 35 miles east of Unalaska, and 766 air miles southwest of Anchorage. Akutan began in 1878 as a fur storage and trading port for the Western Fur & Trading Company. The company’s agent established a commercial cod fishing and processing business that quickly attracted nearby Aleuts to the community. It was the only whaling station in the Aleutians from 1912 to 1942. The U.S. Government evacuated Akutan residents to the Ketchikan area in June 1942.

The village was re-established after the war. Akutan is primarily a non-Native fishing community, although it is home to a traditional Aleut village.

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Commercial fishing and fish processing dominate Akutan’s cash-based economy.

Trident Seafoods operates a major bottomfish plant west of the City. Deep Sea Fisheries also has a permanent processing vessel in the bay. Nine residents hold commercial fishing permits. Subsistence hunting and fishing activities are minimal because the majority of residents are employed. The majority of the population lives in group quarters facilities.

Boats and amphibious aircraft are the only means of transportation into Akutan.

Cargo is delivered weekly by freighter from Seattle. Akutan has no airstrip, however, a seaplane base is available. Daily air service is available from nearby Alaska.

Akutan lies in the maritime climate zone. Temperatures range from 22 to 55. Precipitation averages 27.5 inches per year. Storms are frequent in the winter and fog is common in the summer.

Cyrus Read

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Wolfgang Brinck

Kurt Schmidt participating in the rock toss tradition.

It is said that if you toss a rock on top of the pile of Akutan - and it stays, you will have good luck. Yet, if it falls, you will die within the year.

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Akutan has a deep and protective bay and is actually 40 miles closer to the “crab fishing grounds” than Dutch Harbor. Although Akutan has no landing strip, has only 100 or so fulltime residents, and has no paved roads–only wooden boardwalks, is still one of the busiest fishing ports in the country, and has one of the largest processors–Trident Seafoods–about 1/4 mile away from the village of Akutan. For this reason, and it’s remoteness,it was featured on Deadilest Catch.

First formed in 1878 as a fur trading post, Akutan village was also one of the first introduced to the crab fishing industries in the 1940’s and was home to several floating processors at that time. In 1942, when the Japanese attacked Unalaska, all residents were evacuated and thus had to re-establish themselves as a village in 1944. Finally in 1979, it was incorporated as the “city” of Akutan.

Akutan is not only home to some of the busiest fishing ports, but also superstition.

There is a tradition of throwing rocks onto a rock pile, if the rock stays on top, then you are fine and healthy. However; if the rock falls off, then you will die within the next year.

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Akutan Village

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Pavlof

Elevation: 8261 ft Latitude: 55.4173째 N Longitude: 161.8937째 W The most active volcano of the Aleutian arc

Official Name: Pavlof Volcano Type: Stratovolcano Latest Activity: August 15, 2007

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ty p e : PAVLOF IS A COMPOSITE cone volcano located in the southwestern region of Alaska about 600 kilometers southwest of Anchorage. At its summit Pavlof reaches an elevation of 8,262 ft. The volcano consists of andestic magma, that contains an intermediate content of gases. Emission of lava and ash has occurred during the volcanoes eruptive stage. Other geologic events are also related to the volcanic activity at Pavlof. Seismic activity, mudflows, and flooding have also occurred due to Pavlof’s eruptive process. Pavlof has been in a period of eruptive pause during the previous six weeks. Even during these pauses the threat of violent volcanic activity is always present. Fortunately the volcano is located in a fairly remote region and does not pose a great threat to many people.

Mount Pavlof is a largely snow-covered, cone-shaped mountain with a high ridge extending to the southwest towards Little Pavlof. The volcano is approximately 7 km in diameter and has active vents on the north and east sides close to the summit (McNutt and others, 1991). It is situated high on the northeastern flank of Emmons Lake caldera along a northeast-trending alignment of vents that includes Little Pavlof, Pavlof Sister, and several intracaldera cones. The composite volcano is relatively undissected and is probably Holocene in age. Pavlof lies within the Shumagin seismic gap

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Mount Pavlof is the most active volcano in the Aleutian volcanic arc with almost 40 relatively well-documented eruptions dating back to 1790. It is so consistently active that a question sometimes arises as to what constitutes a separate eruption. Some Pavlof eruptions have been short-lived (1-2 days duration) and similar eruptions in the past may have occurred unnoticed in the sparsely populated region. Pavlof eruptions are typically strombolian to vulcanian in character and consist of rhythmic ejection of incandescent bombs and ash to heights of 200-300 meters above the summit; spatter-fed lava flows emanate from the summit vents on occasion. Short-lived volatile-rich vulcanian ash columns reaching to heights of 10 kilometers or more have been noted, usually at the beginning of an eruption.

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Eruptions tend to be either magmatic or phreatomagmatic and McNutt found a correlation between seismic activity and type of eruption. Strong volcanic tremor accompanied major Strombolian magmatic eruptions, whereas episodes of explosion quakes, with little to no volcanic tremor, were diagnostic of minor phreatomagmatic events. The largest historical eruption of Pavlof occurred on December 6-7, 1911 at the end of a five year period of activity. A

DEFINITIONS

fissure vent opened along the north flank, large blocks were ejected, and lava flows issued from the fissure. A recent vigorous eruptive period began midApril, 1986 and continued through August, 1988. Frequent steam and ash emission, explosions, and strong tremors accompanied summit lava fountaining that fed several agglutinate lava flows, which in turn produced a number of both hot and cold, extensive mudflows.During the early course of the eruption, the eruptive vent shifted from the north to the east side of the summit.

Strombolian Eruptions Strombolian eruptions are relatively low-level volcanic eruptions, named after the Sicilian volcano Stromboli, where such eruptions consist of ejection of incandescent cinder, lapilli and lava bombs to altitudes of tens to hundreds of meters. They are small to medium in volume, with sporadic violence.They are mildly explosive at discrete but fairly regular intervals of seconds to minutes.

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DEFINITIONS

The most recent eruptive episode at Mount Pavlof began about September 11, 1996 and continued into early 1997. The eruptive activity was strombolian in character and similar to most Pavlof eruptions. Intermittent explosive activity and lava fountaining were recorded from two closely-spaced vents high on the north-

Vulcanian Eruptions

west summit of the volcano. Incandescent spatter, spatter-fed flows, and small

A Vulcanian eruption is a short,

lahars moved down the northwest flank of the volcano for the next four months

violent, relatively small explosion of viscous magma .This type of

melting a narrow channel through snow and ice. Occasional elongate plumes

eruption results from the frag-

that rose to a maximum of 10 kilometers above sea level (generally less than 6

mentation and explosion of a plug

kilometers) and extended up to several hundred kilometers downwind were de-

of lava in a volcanic conduit, or from the rupture of a lava dome

tected on satellite images and reported by pilots. These clouds consisted chiefly of

(viscous lava that piles up over a

vapor and gas with minor amounts of ash. Light ash fall was reported on several

vent). Vulcanian eruptions create

occasions from nearby communities.

powerful explosions in which material can travel faster than

Mount Pavlof is composed of basaltic andesite flows and pyroclastic rocks that

800mph and rise several kilome-

overlap similar rocks from nearby Little Pavlof. The flows are moderately phyric

ters into the air. They produce

with about 25% phenocrysts, mostly plagioclase with minor olivine and clinopy-

tephra, ash clouds, and pyroclastic density currents.

roxene. The agglutinate flows of 1987 are of similar andesitic composition.

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DEFINITIONS

The volcano is 7km in diameter and has two active vents, one located on the northern side and the other on the eastern side (Miller et al, 1998) and the overall

Phreatomagmatic Phreatomagmatic eruptions are defined as juvenile forming

outline of the volcano appears cone shaped.

eruptions as a result of interaction between water and magma. They

Pavlof has been erupting since 1790 and has experienced more then forty periods of small to moderate activity since this time (Decker & Decker, 1998) with the

are different from magmatic and phreatic eruptions. The products of phreatomagmatic eruptions

latest eruption occurring from September 1996 to January 1997 (Wallace et al,

contain juvenile clasts, unlike

2000). The type of eruptions normally seen from Pavlof consist of Strombolian

phreatic eruptions, and are the

and Vulcanian eruptions where the main components are bombs and ash that

result of interaction between magma and water, unlike magmatic

normally reach heights of around 200 to 300m (Miller et al, 1998).

eruptions.It is very common for a

The largest eruption in Pavlof’s history occurred in 1911 when a fissure opened

large explosive eruption to have

expelling large lava flows, together with these flows large blocks were expelled from the volcano. In more recent times a period of high activity was noted from 1986 through to 1988 where large volumes of ash and steam were expelled together with lava flows and also lava fountains.

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magmatic and phreatomagmatic components.

eruptions and activity

Start Date: 08.15.2007 Stop Date: 09.13.2007 Volcanic Explosivity(VEI): 2 Eruptive Characteristics:

During the night, an intense thermal anomaly (TA) was visible in satellite images

Central vent eruption

(Advanced Very High Resolution Radiometer-AVHRR), and seismic activity contin-

Explosive eruption

ued to increase in both number and duration of events per hour, clear signs that the

Lava flow

unrest was escalating. On the morning of August 15, based on observations of the

Mudflow

TA and increasing seismicity, AVO elevated the Aviation Color Code/Volcano Alert Level to ORANGE/WATCH and announced that an eruption was expected. With the upgrade in color code, AVO began 24-hour surveillance of the volcano. Later in the day, AVO received eyewitness accounts from mariners of incandescent blocks rolling down the eastern-southeastern flank of the volcano during the previous night, beginning around midnight. Pilots reported a thin, low-level ash plume extending a few kilometers southwest from the summit. After receiving these reports, AVO established that the volcano was in eruption. Aerial photographs taken on August 15 show lava fountaining from a vent located about 650 ft below the summit.

On August 16, strong seismic signals recorded at a single station, located 5.3 mi southeast of the summit, heralded the passage of lahars down the south flank; more than 41 lahar events would be recorded by this station over the next 29 days. Satellite observations of a strong thermal anomaly and nighttime incandescence at the 38

summit reported by local residents were indications of vigorous lava eruption at the summit vent. The seismic network recorded long periods of volcanic tremor with repetitive explosions that indicated nearly continuous Strombolian eruption. In addition to the generation of lahars, this activity produced low-level ash clouds, and a spatter-fed lava flow that descended the southeastern flank. By August 18, AVO personnel in the field reported that vigorous eruption of lava at the summit continued.

Using a Forward Looking Infrared (FLIR) camera, they determined that a 20- to 50-m-wide, 65- to 165 ft-wide) 600 C (1,112 F) lava flow extended 565 m (1,850 ft) from the vent down the southeast flank [see figs. 29 and 30 in original text]. Thermal data collected the next day indicated that the outer part of this flow was about 140C (284 F) and had cooled considerably. The vent crater for the last eruption of Pavlof, in 1996, was located on the upper northwestern side of the summit. For this eruption, the active vent migrated to the upper southeastern side, about 200 m (650 ft) below the summit.

Seismicity at Pavlof was elevated and steady throughout the remainder of August and then began waxing and waning for the first week of September. A strong TA was present in satellite images, even through clouds, during this time. During the second week of September, the seismicity began showing signs of a steady decrease, and by September 13, seismicity decreased to low levels and only a minor steam plume was visible above the volcano.

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“ Ash, a blocky lava flow, and multiple lahars were generated by this eruption. Mixed ash and steam clouds produced during the most energetic eruptive period, mid-August to mid-September, reached altitudes of 5-6 km (about 20,000 ft) ASL. The plumes were diffuse, drifted primarily to the southeast over the North Pacific Ocean, and many could not be detected in satellite imagery. No ash reportedly fell on nearby communities and there were no significant impacts to aviation. AVO deployed a DRUM aerosol impactor (particle collector) in Sand Point, 90 km (56 mi) east of Pavlof, and collected fine ash.

Although no visible ash fallout was observed during aerosol sampling, these results demonstrate that volcanic ash was present in respirable size fractions downwind of the volcano even during periods of low ash emissions

Analyzed samples from the lava flow are basaltic andesite in composition (53% SiO2), which is similar to the products of previous Pavlof eruptions.Lahars were produced by interaction of hot blocks and spatter from the lava flow with snow and ice on the southeastern flank. The lahars inundated an area over 2 km2 (0.78 mi2) and formed a debris fan that extended 3.6 km (2.2 mi) from the base of the volcano into Pavlof Bay .

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DEFINITIONS

SIO2 Silicon dioxide (Chemical Compound) Silicon dioxide, also known as silica, is a chemical compound that is an oxide of silicon with the chemical formula SiO2. It has been known for its hardness since ancient times.

Plumes A volcanic plume is a mixture of particles and gas emitted by an eruption. Plumes may reach heights of 80 km in large eruptions. The plume is generated by fragmentation of magma.

The plume has 3 phases.

Jet Phase is dominated by upward momentum.

Convective Phase is where the plume rises by convection.

Umbrella Phase is where the plume spreads out.

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Start Date: 01.2001 Eruption is UNCERTAIN Volcanic Explosivity (VEI): 1 Eruptive Characteristics: Central vent eruption Hydrothermal activity Steam

McGimsey and others (2004) summarize 2001 steaming and other activity at Pavlof as follows: “Principal/Teacher, John Concilius, has a good view of Pavlof from his home in Nelson Lagoon. On January 20, 2001 he observed through binoculars steaming from multiple locations near the summit, but none actually at the top of the volcano. He reported that the steam was white and not discolored, and, that the snow near the summit was clean with no evidence of melting.

He concluded by stating that this was the most steaming he had seen at the volcano during the past several years and that other villagers considered the steaming to be unusual.AVO remote sensing specialist Dave Schneider analyzed Advanced Very High Resolution Radiometer (AVHRR) satellite images taken from January 18 to 22, 2001 and found no evidence of increased thermal activity at the volcano and no unusual seismicity was noted. No further reports of steaming were forthcoming.

This may have been a meteorological phenomenon.While working in Cold Bay in early June, Martin LaFevers, Seismic Data Manager at UAFGI, observed and photographed the summit of Pavlof during a weather break; it appeared to be covered with ash. A local pilot reported seeing ‘something other than steam’ at the summit.

Again, there was no indication of anomalous seismicity.

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Start Date: 09.11.1996 Stop Date: 01.03.1997 Volcanic Explosivity (VEI): 2

Pavlof Volcano, historically the most active volcano in the Wrangell-Aleutian volca-

Eruptive Characteristics:

nic arc, began a vigorous strombolian eruption in mid-September, 1996. The erup-

Central vent eruption

tion, which continued into early 1997, occurred only two months after a 6-station

Explosive eruption

seismic network was established near the volcano.

Lava flow

A NW observer in Cold Bay noted steam and incandescent ejecta above the volcano

Mudflow

at about 0830 ADT on September 16. Analysis of seismic data and satellite images suggest that the eruption likely began at a very low level by September 11. Over the next few weeks, nearby residents observed intermittent strombolian eruptions from near the summit of the volcano. Pilots reported incandescent bombs the size of pick up trucks accompanied by minor ash clouds alternating with steam plumes rising from a few hundred meters to approximately 2 km above the volcano.

Photographs from overflights on September 23 and AVO video from September 2730 showed lava fountains emanating from two vents. One vent was located on the east edge of an ~150-m diameter crater that indented the northwest summit of the volcano. A second, more active locus of fountaining was perched on the west edge of this crater 100-150 m below the summit. The two loci of fountaining were about 100 m apart and were generally not synchronous in activity. The east vent was less vigorous overall, producing intermittent puffs of gray to dark gray ash and steam tens of meters high. The west vent was the source of intermittent bursts of incandescent spatter up to 300 m high.

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By September 23, a small spatter cone was forming at the west vent and a collar of spatter, spatter-fed flows, and small lahars extended about 500 meters down the 30 degree northwest flank below the summit crater. A lava flow formed by the coalescence and remobilization of heavy spatterfall and direct spill over from the west vent plunged down the steep flank, melting a narrow channel through seasonal snow and glacial ice. By September 29, the lava flow had reached the base of the cone, about 3.5 km from its source, and was beginning to widen into a lobate fan.

Dark lahar deposits extended beyond the toe of this lava flow across the gently sloping ground northwest of the volcano, coming within about 40 m of AVO’s seismic station PV6. By late October, a second lava flow issued from the east vent and on December 2, when videotaped by Alaska State Troopers, this flow was the more active of the two and had nearly reached the base of the cone in the saddle between Pavlof and Pavlof Sister.

Eruptive activity became intermittent during the month of December. Seismicity decreased abruptly early on December 4 and ash was not visible above the regional cloud cover that obscured the summit of Pavlof for several days. Brief episodes of heightened seismicity occurred on December 10 (accompanied by at least one pilot report of ash) and December 27. The last reliable observation of ash emission occurred on January 3, although pilots and observers in Cold Bay reported possible minor ash in the steam plume over the volcano on a few occasions through February 6. Collapse of unstable agglutinate and hot fragmental debris on the steep upper cone may well account for some of these small ash plumes.

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During the first two weeks of the eruption, occasional elongate clouds containing minor amounts of ash were detected on NOAA AVHRR satellite images. During the third week, both pilot reports and satellite image analysis documented larger but still diffuse ash clouds trailing as far as 175 km downwind, but they rarely reached more than ~6 km above the sea level. These clouds varied in length from a few tens to several hundred km and were observed intermittently, weather permitting, through late December. On November 4, accompanying some of the strongest seismicity of the eruption, a plume was visible in Bands 4-5 extending 350 km northeast of the volcano.

In addition to elongate plumes, thermal anomalies associated with high temperature material were also recorded near the volcano’s active vents and along the two main lava flow paths. The number of saturated pixels on AVHRR images varied from 1 - 15 indicating areas of up to about 18 km2 above 37 degrees C (A.L. Roach, oral communication, 1997). The last significant thermal anomaly was recorded in late December, however “warm” pixels were noted during daily analysis of AVHRR data into mid-February. Pilot reports and observations from Cold Bay confirm continued warm ground around the summit of the volcano as inferred from areas of snow-melt.

As in the 1986 eruption, the 1996 activity produced rubbly, fragmental lava flows that extend in two main lobes down the northwest flank of the volcano. Early in the eruption, these flows occupied, at least in part, channels cut into the seasonal snow and glacial ice on the volcano’s flank. Melting of this snow and ice produced water 47

and rock mixtures of unknown consistency that flowed out onto the more gently sloping terrain northwest (and possibly northeast) of the volcano. As of this writing, we do not know how far these lahars traveled or what impact they had on the Cathedral River and other drainages around Pavlof. Very light ashfall was reported in King Cove on the night of October 5-6, Sand Point on October 19, and Nelson Lagoon on October 28.

More from Neal and McGimsey (1997): “On October 3, based on observed plume heights, the FAA issued a Notice to Airmen (NOTAM) restricting flight below ~7 km and within 10 nautical miles of Pavlof. Higher levels of seismicity and more energetic ash plumes began on October 15 and in response, the FAA increased the alti-

DEFINITIONS

Lahar A lahar is a type of mudflow

tude of restricted air space to approximately 8 km and the size of the restricted zone

or debris flow composed of a

to a 25 mile radius around Pavlof. The FAA continued to enforce this restriction

slurry of pyroclastic material,

until January 27, 1997. Although Pavlof ash plumes reached altitudes of 30,000 feet

rocky debris, and water. The material flows down from a

or more on a few occasions, there were no serious disruptions in the North Pacific

volcano, typically along a riv-

airways. There were, however, impacts on local air traffic. On November 4, a United

er valley. Lahars are extremely

States Coast Guard (USCG) C-130 operating at low level over the Bering Sea was

destructive: they can flow tens of meters per second, be 460

struck by lightning. The flight crew also reported a “smoky” smell in the cockpit

ft deep, and destroy any struc-

and a fine dust throughout the plane. Subsequent discussion with the USCG failed

tures in their path.

to positively identify the source of this material. However, based on NWS forecast winds during the time of this report, it appears unlikely that primary ejecta from Pavlof could have been the culprit; rather, it is possible that low level winds remobilized fine ash from the ground.

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Start Date: 01.05.1990 Stop Date: 03.05.1990 Volcanic Explosivity (VEI): 2 Eruptive Characteristics: Central vent eruption Explosive eruption

“ Pavlof Volcano has been quiet since August 1988. On January 5 and 6, 1990, Marsha Brown of the FAA flight service at Cold Bay observed traces of steam rising up to 100 m above the NE summit vent that was trailing to the NE. The top of the volcano was dark due to the melting of snow around the summit vent. The volcano has been pure white with snow for the winter up to this time. On March 5, several eruption plumes were observed.

”

— Steven McNutt

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Start Date: 04.16.1986 Stop Date: 08.13.1988 Volcanic Explosivity (VEI): 3 Lava Volume: 7.8 x 106 m3 Eruptive Characteristics: Central vent eruption Flank vent Explosive eruption Pyroclastic flow Lava flow Lahars

The visual observations of the 1986 eruptions, both aerial and on the ground, provide information generally lacking from previous historic eruptions. The physical characteristics of of the 1986 eruption are probably similar to other historic summit eruptions, although the 1986 activity was more explosive and of longer duration.

The 1986 activity was chiefly Strombolian, characterized by sporadic emissions of dark ash to heights of up to 5 km; one exceptionally strong (probably Vulcanian) eruptive event sent an ash column to over 15 km on 18-19 April. The initial phase of the eruption appears to have involved the summit vent on the north side of the volcano which has been the site of all Pavlof eruptions since the mid-1960s. This eruptive phase lasted from 16 to 26 April and included a hot rootless agglutinate flow that extended down the northwest flank of the volcano.

The deposit was actively degassing steam along its entire length in late June. It had an estimated volume of about 4x10^6 cubic meters and, at an elevation of 760 meters, was 20-30 meters thick and 40-50 meters wide. The deposit was clast-supported and fines-depleted, consisting entirely of glassy, slightly vesicular andesitic basalt (SiO2 = 53.5%) bombs and irregular masses of spatter with a maximum diameter of about 1.2 meters. It was probably emplaced during the initial and relatively violent vent-clearing phases of the eruption on 16-28 April. Associated hot lahars caused melting of snow and ice and extensive flooding in the Cathedral River drainage north of the volcano.

Heavy ash fall occurred north and west of the volcano during the April activity; 2-3 mm of ash fell on the nearby communities of Cold Bay, 35 km to the west, and King Cove, 48 km to the southwest, but caused no damage.

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Eruptive activity began again in late May and was highlighted by sporadic, but vigorous Strombolian eruptive activity and by the formation of a new vent high on the east flank of the volcano. Comparison of aerial photography indicated that this is the first major change in the vent geometry of Pavlof since the early 1960s. The period of activity was characterized by repeated small bursts of ash and cinder to a few hundred meters above the vent and spatter tossed a few tens of meters all accompanied by explosive, thunderlike reports. The explosions characterizing the Strombolian eruption occurred at intervals of 5-15 seconds during the half dozen times the new DEFINITIONS

vent was observed between 14 June and 30 June, suggesting a moderately rapid rate

Pyroclastic Flow

of magma rise in the conduit. Only minor ash emission was observed associated

A pyroclastic flow is a fast-mov-

with the explosive ejection of incandescent bombs from the new vent. Activity from

ing current of hot gas and rock (known as tephra), which reach-

the old north vent during this time consisted of steam emission with little or no ash.

es speeds moving away from a volcano of up to 450 mph.The gas can reach temperatures of about 1,830 °F. Pyroclastic

The nature of the material in the flow at this elevation and the physical characteristics of the spatter rampart at the vent strongly suggest that much of the lower

flows normally hug the ground

part of the flow may have resulted from similar pyroclastic flow activity following

and travel downhill, or spread

partial collapse of the oversteepened spatter rampart. Throughout the course of the

laterally under gravity.

eruption, the steep spatter rampart may have periodically become unstable and collapsed, either in whole or part, forming hot, disaggregated pyroclastic flows cascading down the chute. Where ice and snow were overrun by the hot debris, mudflows were generated that continued to travel down and fan out on the volcano’s lower 51

slopes. In support of this hypothesis, a pyroclastic flow was observed on 19 June moving down the same chute from about 1400 m elevation to about 900 m; the upper 1100 m of the volcano was cloud-covered at this time.

An alternative scenario is that the pyroclastic flow observed on 19 June resulted from a ‘boil-over’ of the magma column at the vent following a larger-than-usual explosion. Although no seismic evidence for such an explosion was observed, the obscuring cloud cover prevents an exact explanation for the origin o fthe observed pyroclastic flow.

The April-August eruption is similar to, but somewhat stronger than most of the other Pavlof eruptions of this century (Simkin et al., 1981; McNutt 1987a) in terms of its Strombolian character. The duration of the eruption, as indicated by lava fountain activity and spatter ejection, however, appeared to be much longer than for most modern eruptions. This eruption also altered the physiography of the summit area by forming a new vent. In contrast to most recent eruptions (i.e., 1973-1983) that occurred in the fall of the year, the 1986 eruption was concentrated in the spring and summer.”

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Start Date: 11.11.1983 Other Eruptions Stop Date: 12.181983 1982 Jul 15

Volcanic Explosivity (VEI): 3

1981 Sep 25

Area of Activity: NE FLANK

Eruptive activity was first observed from Sand Point late on 14 November and pilots observed tephra columns the next afternoon. On 19 November a small vapor cloud rose approximately a hundred meters above the vent. Bad weather prevented observations until 26 November when Pavlof was visible until mid-afternoon from Cold Bay. During the morning, a vapor plume containing a little ash rose to 4.5 km altitude.

1980 Nov 8 1980 Jul 6 1975 Sep 13 1974 Sep 1 1974 Mar 12 1973 Nov 12 1966 Mar 15 1958 May 17 1953 Nov 25 1951 Oct 3

At intervals of approximately 30 minutes, puffs of dark ash

1950 Jul 31

were emitted. The intervals became shorter, and by 1500 ash

1936 - 1948,

emission was nearly continuous.

1929 Mar 1 1924 Jan 17 1922 Dec 24

Its amplitude gradually increased, and tremor began to saturate the seismograph at 1100 on 14 November. Tremor was strongest between midnight and 1200 on 15 November, and continued to saturate the seismograph until 2100 on 15 November when its amplitude began to decrease.

1914 Jul 6 1906 - 1911 1901 1894 1892 1880, 1866 Mar 14 1852 1846 Aug 15

53

54

culture Pavlof Bay

THE MAIN CHALLENGE of climbing this peak is its remoteness and the consequent difficulty of access. The peak is a 30 mi journey from the north side of Cold Bay. The climb itself is a straightforward snow climb, and the ski descent is recommended The volcano is below the path of hundreds of daily international flight paths, and an explosive eruption could interrupt those operations, said Steve McNutt, a volcano seismologist with the observatory. Volcanic ash can enter an engine and make it seize up, he said.

Pavlof Bay is an inlet in Alaska located on the southwestern edge of the Alaska Peninsula. It is on the peninsula’s south coast, is about 50 miles long, and lies directly north of the Pavlof Islands. The 8,261-foot volcano Mount Pavlof is on its western shore.Pavlof is about nine miles from Pavlof Bay, a popular fishing ground. Pavlof Bay, on the southern side of the Alaska Peninsula, supported one of the world’s largest pandalid shrimp fisheries until 1979, and about 70% of the catches consisted of the northern shrimp.

The English name for the island comes from Pitka Pavalof, a Creole of Russian-Native. In 1893, Pitka Pavalof and Sergei Gologoff Cherosky, Creoles of Russian-Native descent, found gold on Birch Creek in Interior Alaska. Learning of 55

the discovery, prospectors jumped their claims and argued that the claims were invalid because the men were Natives. The discovery attracted more non-Natives to the Yukon River and the town of Circle was founded are a group of culturally similar indigenous peoples inhabiting the Arctic regions of Greenland, Canada, the United States, and Russia. Inuit is a plural noun; the singular is Inuk. The Inuit languages are classified in the Aleut family.

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USGS

“ The mountain burst with a loud ‘cannonade’ at this site [eastern slope of the mountain, where a pre-existing lava flow was] in August, 1846. Smoke poured out in clouds from a fissure, ash fell, and flames appeared. Flames also shot up from the summit.

A northwest wind dispersed both the smoke and the ash that obscured from the inhabitants of Pavlof the islands at the mouth of the bay. The ash was carried to the village of Pavlof, where it was necessary to place a covering over the fish that were hung up.

Smoke and ash were carried to Unga Island (about 85 kilometers to the east), where people also protected drying fish from ash by covering it with matting.

”

- Steven McNutt

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Lahar deposits after eruption in 2007

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Chris Waythomas

Shishaldin

Elevation: 9373.3ft Latitude:

54.75째 N

Longitude: 163.97째 W

The highest volcano in the Aleutian Islands.

Official Name: Shishaldin Type:

Stratovolcano

Latest Activity: 2008

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ty p e :

MOUNT SHISHALDIN IS a moderately active volcano on Unimak Island in the Aleutian Islands chain of Alaska. It is the highest mountain peak of the Aleutian Islands. The most symmetrical cone-shaped glacier-clad large mountain on earth, the volcano’s topographic contour lines is nearly perfect circles above 6,500 feet.

The lower north and south slopes are somewhat steeper than the lower eastern and western slopes. The volcano is the westernmost of three large stratovolcanoes along an east–west line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning “mountain which points the way when I am lost.”

The upper 2,000 meters is almost entirely covered by glacial snow and ice. In all, Shishaldin’s glacial shield covers about 35 square miles. It is flanked to the northwest by 24 monogenetic parasitic cones, an area blanketed by massive a lava flows.

The Shishaldin cone is less than 10,000 years old and is constructed on a glacially eroded remnant of an ancestral soma and shield. Remnants of the older ancestral volcano are exposed on the west and northeast sides at 1,500–1,800 meters elevation. The Shishaldin edifice contains about 300 cubic kilometers of material.

A very steady steam plume rises from its small summit crater which is about 500 feet across and slightly breached along the north rim. This volcano has had many recorded eruptions during the 19th and 20th centuries, and a couple reports of volcanic activity in the area during the 18th century may have referred to Shishaldin as well. Therefore the volcano’s entire recorded history is spotted with reports of activity. AVO has 24 confirmed eruptions at Shishaldin, making it the volcano with the third most confirmed eruptions (after Akutan and Pavlof). However, Shishal64

din has the most eruptions (this means confirmed AND possible eruptions) in Alaska, but half of the eruptions are unconfirmed, with the most recent one being in 2008. Mount Shishaldin’s most recent eruptions were in 1995–96 and 1999.

Since the 1999 eruption, it has maintained seismic activity, typically having very low-magnitude volcanic earthquakes (most are below magnitude 1) every 1–2 minutes. During this period of non-eruptive seismic activity, it has been puffing steam, with puffs also occurring about every 1–2 minutes. There were reports in 2004 of small quantities of ash being emitted with the steam.

The Alaska Volcano Observatory monitors the volcano for more hazardous activity with seismometers and satellite images. Visual observations are rare, because of the remote location of the volcano

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eruptions and activity

2008 Activity An ash plume rising to 3 km altitude was visible at the volcano on 12th February.

2004 Seismic Unrest In early May tremor was observed at the volcano for the first time since the 1999 eruption, and continued until June. In July the crater rim was warmer than the surrounding area.

1999 Eruption The 1999 eruption was the largest known at the volcano in the 20th century. Starting in late June 1998, a swarm of low-frequency events was detected beneath the volcano. Observations of unusual activity at Shishaldin volcano be gan with a report by the US Coast Guard of steam and ash plumes “puffing� at 10-min intervals to about 30 m above the vent on 5th November 1998.

On 17th April 1999 Strombolian eruptions were detected using Forward Looking Infrared Radiometer on board an aircraft.

The main phase of the eruption was sub-Plinian and changing Strombolian eruptions after 80 minutes. The eruption ended on 24th April 1999.

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diaster preparedness Other Eruptions

2008

Although the Shishaldin Volcano is not very explosive, possessing basaltic lava, which is extremely dense. When erupting,

1999 1995 1993

the volcano can spew ash 20 kilometers into the air, making

1986-87

any air traffic potentially lethal. Ash clouds can destroy plane

1979

engines and other electronics, and ash clouds can drift and

1975 1967

affect other, further, nations. Eruptions can also melt polar ice-

1963

caps, causing massive flooding, as well as lahars, which are

1953

mudslides made of volcanic fragments. Pyroclastic flows are

1951 1946-47,

also common. They are strong and incredibly hot surges of

1932

semi solid material and they destroy everything in their path.

1929 1901

Lava flows are also common.

1898 1883

Although local towns are generally out of the volcano’s sometimes destructive path, precautions are taken by the Federal Aviation Adminstration (FAA) and the USGS to prevent potential danger to air travelers.

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1842 1838 1830 1824

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culture Shishaldin Volcano

The Shishaldin Volcano affects the environment in both positive and negative ways. Harmful gases are emitted into the air during eruptions and stay in the air for long periods of time. Shishaldin can cause large pyrocalstic flows but, luckily, it is far enough away from any major towns to prevent any catastrophic damage.

Few people visit the mountain and there are no towns near enough to be harmed

Unimak Island is the largest island in the Aleutian Islands chain of the U.S. state of Alaska. It is the easternmost island in the Aleutians and, with an area of 1,571.41 mi(4,069.9 km), the ninth largest island in the United States and the 134th largest island in the world. It is home to Mount Shishaldin, one of the ten most active volcanoes in the world. According to the United States Census Bureau, there were 64 people living on Unimak as of the 2000 census, all of them in the city of False Pass at the eastern end of the island. Cape Lutke is a headland on the island.

An interesting physical feature is Fisher Caldera, a volcanic crater in the west-central part of Unimak. Some characteristics include many volcanic cones and undrained lakes. It is named for Bernard Fisher, a U.S. Geological Survey 69

geologist who was killed in Umnak Pass. As a faunal extension of the Alaska Peninsula, Unimak has a relatively diverse assemblage of terrestrial mammals, including brown bears and caribou. West of Unimak, the largest native mammal in the Aleutians is the red fox.

Scotch Cap Lighthouse was built in 1903 and was manned by the U. S. Coast Guard. On April 1, 1946, during the 1946 Aleutian Islands earthquake, the lighthouse was struck by a tsunami. Even though the lighthouse was 98 feet (30 m) above the sea, the lighthouse slid into the sea, killing five Coast Guard personnel

False Pass (Isanaxin Aleut) is a city in Aleutians East Borough, Alaska, United States. Isanax is the Aleut name for present day Isanotski Strait and means gap, hole, rent, or tear in the Aleut language which was rendered as Isanotski (or Issanakskie, Isanotskoi, Isanakh etc.) in transliterated Russian. The first of the Aleutian Islands and it connects the northern Gulf of Alaska with the Bering Sea. This strait was used for safe passage for millennia by Aleuts and later by the Russians during their occupation of the area. The strait is used today by most vessels less than 200 feet in length traveling to and from northern Alaska and points in southwest and southeast Alaska and the “lower 48” states.

False Pass is an early English name for Isanotski Strait on which the City of False Pass is located. The strait was called “False Pass” by early American sailing ship captains because it was thought to be impassable for their deep draft 70

vessels at the northern end. A salmon cannery was built on the Unimak Island side of the strait in 1919 which provided the nucleus for the modern settlement. A U.S. post office with the name of False Pass was established in 1921 which gave official status to the community.Commercial fishing for salmon, cod, halibut and crab continues to be the core of the community’s lifestyle and economy. The city population was 35 at the 2010 census is near the eastern end of Unimak Island, in the Aleutian Islands chain. Part of the city (10.075 sq mi) is actually on the westernmost tip of the mainland Alaska Peninsula, across the Isanotski Strait, although that section is nearly unpopulated. The city boundaries include the abandoned villages of Morzhovoi and Ikatan.

As of the census of 2000, there were 64 people, 22 households, and 13 families residing in the city. The population density was 2.4 people per square mile. There were 40 housing units at an average density of 1.5 per square mile. The racial makeup of the city was 62.50% Native American, 26.56% White, 1.56% from other races, and 9.38% from two or more races. 1.56% of the population were Hispanic or Latino of any race.

Boats and aircraft are the only way to get to False Pass. Aircraft use False Pass Airport. The first period and the one that lasts the longest, is the Aleut Period.

The Aleut peoples arrived in this area, probably from Siberia across the “Bering Land Bridge� some 10,000 years ago. They dominated this area until the arrival of the Russian explorers in 1741. The Aleuts lived in this area in relative stability and abundance for a continuous period longer than most other peo71

ples on earth inhabited their homelands. This is an amazing testimony to their skills and cultural coherence.

The second period is the period of immigrants, starting when the Russians arrived to exploit the Sea Otter and other fur bearing animals and establish outposts here. The Russians arrived in 1741 with Vitus Bering and stayed until Alaska was purchased by the Americans from the Russian Crown for 7.2 million dollars on April 4, 1867. The third period begins to focus on the first externally-based economy for the area, the fishing of Cod. The Codfish industry was established mostly by immigrants and visitors from Seattle and San Francisco. Many immigrants, mostly from Scandinavia came here and settled in areas where Cod was readily available on nearby fishing grounds.

The fourth period signals the arrival of the canned salmon processsors, primarily from the Seattle area of Washington. This begins the actual history of False Pass as a community, with the establishment of a salmon cannery on the site in 1919 by P.E. Harris Co.Bridging the time period of codfishing and salmon fishing is the fur trapping period. Many local men fished during the summer season when salmon and cod were available and trapped for fur-bearing animals during the winter months. During some years they made more trapping than fishing.The final period and the one we are still in, is the Modern Period, which is characterized by a diversified fisheries economy oriented towards the export and globalized market.

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mount cleveland

elevation: 5676 ft latitude:

52.8222째 N

longitude:169.945째 W

The island is completely uninhabited

official name: Shishaldin type:

Stratovolcano

latest activity:July 19, 2011

77

ty p e :

Mount Cleveland is a nearly symmetrical stratovolcano on the western end of Chuginadak Island, which is part of the Islands of Four Mountains just west of Umnak Island in the Fox Islands of the Aleutian Islands of Alaska. Mt. Cleveland is 5,676 ft high, and one of the most active of the 75 or more volcanoes in the larger Aleutian Arc.

In 1894 a team from the U.S. Coast Guard and Geodetic Survey visited the island and gave Mount Cleveland its current name, after President Grover Cleveland.

One of the most active volcanoes in the Aleutian Arc, Cleveland has erupted at least 21 times in the last 230 years. A VEI 3 eruption in 1944 produced the arc’s only direct volcanic fatality. Most recently Mount Cleveland has erupted three times in 2009, twice in 2010, and once in 2011.The volcano’s remoteness limits opportunities for its study, and the Alask a Volcano Observatory relies heavily on satellites for monitoring. The volcano is primarily hazardous to aircraft; many of the flights over the north Pacific approach the vicinity of the volcano, and volcanic ash released from eruptions can damage sensitive electronic equipment and sensors.

Mount Cleveland is located 304 mi from the western end of the Aleutian Arc, a long volcanic chain extending off the coast of Alaska. Containing over 75 volcanoes, this volcanic arc occurs above the subduction zone where the Pacific Plate plunges under the North American plate. As the plate moves deeper into the 78

Islands of Four Mountains, a volcanic group in the Aleutian Arc. Like all stratovolcanoes, Mount Cleveland grew as explosive eruptions, effusive eruptions, and lahars built it layer by layer into a concave-up shape. It lies southeast of Mount Carlisle and northeast of Herbert Island. Mount Cleveland forms the western half of Chuginadak Island, a broad and uneven bell-shaped landmass, and is the highest of the four volcanic islands.The island is completely uninhabited; the nearest settlement is Nikolski on Umnak Island, about 47 miles eastward.

Mount Cleveland is 5.0–5.3 mi wide at its base and roughly 7 cubic miles in volume. The volcano’s slope increases markedly with height, from 19° at its lower flanks to 35° near its summit. Like many other Aleutian volcanoes, Cleveland’s flanks are especially rough up to 984 ft, covered by multiple overlapping lava flows and debris fans that form an apron around the mountain. Lava flows are always built on top of debris flows as a result of the snow melt caused by the emission of heat just before an eruption. The flows are generally short, under 0.6 mi, and thin, less than 33 ft thick, and are somewhat vegetated.

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Although Mount Cleveland is the tallest mountain in the group, it is rarely completely snowed in because of its constant activity disrupts snowfall. A lack of extant erosion shows that Mount Cleveland is likely a Holocene volcano, forming within the last 10,000 years.All known events have occurred at Mount Cleveland’s summit vent, but there are at least five small andesite to dacite volca-

DEFINITIONS

nic domes on the lower flanks. At times Cleveland has had a summit lava dome. The volcano has no caldera.

Isthmus a narrow strip of land, bordered

The eastern half of Chuginadak, to which Mount Cleve-

on both sides by water, connecting

land is connected by a narrow isthmus, consists of sev-

two larger bodies of land.

eral low-lying volcanic cones and two prominent peaks that have been heavily eroded, partly by glaciers. Known as the Tana volcanic complex, the two features measure 3,839 ft and 3,586 ft in elevation. A sample of rhyolite has been recovered from Concord Point, the easternmost Mt. Cleveland’s Isthmus

point on the island.

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eruptions and activity

DEFINITIONS

Eruptions from Mount Cleveland are generally vulcanian and strombolian in nature, characterized by short explosive

A’A Basaltic lava forming very rough

ash clouds sometimes accompanied by a’a flows, lava foun-

jagged masses with a light frothy texture. ‘A’a flows are character-

tains,pyroclastic flows, ash and steam emissions, lava dome

ized most obviously by very rough top surfaces, dense interiors, and

growth, and the ejection of breadcrust bombs. Hot springs were reportedly found on the volcano in the 1800s, and persistent fumarolic activity was observed in the 1980s and 1990s. Mount Cleveland is a site of persistent steam emissions and thermal anomalies that represent constant background activity. During 2011, a summit lava dome formed, by continuous intrusion of magma at the summit. Late in 2011, nearly 6 explosions demolished the dome. Little is known 82

sometimes rough bottom surfaces.

about Cleveland’s early eruptive history as its remoteness makes it a difficult area to investigate, and discrepancies in names have caused confusion between events there and those on nearby Carlisle. Even today, not all possible events are confirmed as eruptions by the Alaska Volcano Observatory, and many are listed as “possible.” In observed history, Mount Cleveland may have first erupted in 1744; the first confirmed eruption occurred in 1828. The volcano erupted again in (1836, 1893, 1897, 1929, 1932, and 1938 possibly).

The first notable eruption from Mount Cleveland was a Volcanic Explosivity Index (VEI) 3 Vulcanian eruption that occurred between June 10 and June 13, 1944. Lava flows extended 3 miles from the summit, and an ash plume 19,685 feet high was produced. Large boulders were reportedly ejected and carried out to sea by eruptive force. The eruption had the distinction of being the only confirmed direct volcanic fatality in Alaska; a small detachment from the Eleventh Air Force was stationed on the volcano at the time, and one Sergeant Purchase left his post early in the eruption to take a walk and never returned, probably killed by mudslides. The island was abandoned for the remainder of the war.[20] Mount Cleveland erupted more recently in 1951, 1953, 1954 (possibly), 1975 (possibly), 83

1984 through 1987, 1989, 1994, and 1997. The volcano has received more focused attention in recent times due to its increased activity: it erupted in 2001, 2005, three times in 2006, 2007, three times in 2009, and twice in 2010. Of these, the most significant eruption was the 2001 eruption, which produced a 12 km (7 mi) high ash plume. This plume dispersed 120 to 150 km (75 to 93 mi) across Alaska, an unusual distance that allowed detailed satellite observations to be made.[4][9] Nikolski and the surrounding region was the site of several hours of ashfall, represented in satellite imagery as areas of discolored snow.[14] This eruption significantly disrupted air traffic in the area.[4] On June 19, 2012, a pilot reported an ash-producing explosion on Mount Cleveland. Due to continuing seismic activity, the volcano was placed on the USGS Volcano Watch List in the orange or “watch� category the following day. AVO continues to keep Cleveland on the watch because of a persistent anomaly at the summit. AVO suspects it could be dome growth. Other minor ash producing explosions occurred on June 26, July 12, and most recently, August 19. In total the volcano has erupted at least 22 times in the last 230 years.

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2011 - 2012 Eruptions On December 29, 2011, AVO observed a detached, drifting ash cloud to approximatly 15,000 ft ASL in satellite imagery. The plume was approximately 50 miles moving east from Cleveland.

Ground-coupled airwaves from the explosion were also detected at the distant Okmok seismic netowork - placing the time of explosion at 13:12 UTC, December 29. Based on the presence of an ash cloud, AVO raised the aviation color code back to ORANGE and the alert level to WATCH.

One month later, on January 30, 2012, satellite data showed another small dome within the summit crater. As of January 30, 2012, the new dome measured about 40 meters in diameter. On January 31, 2012 AVO raised the aviation color code to ORANGE and the volcano alert level to WATCH. By February 10, 2012, the lava dome’s size was estimated at 50 m in diameter, and it had grown to 60 m by February 17.

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On March 8, 10, and 13, 2012, there were three small, short-duration explosion at Cleveland; detected by distant infrasound and seismic sensors. These explosions likely expelled the dome that had been in the summit crater.

On April 4, 2012, this new dome, which had grown to about 70 m in diameter, was destroyed during a short explosive eruption. This eruption was detected by distant infrasound and seismic stations, and had an ash cloud height of about 4.5 km. This was the third lava dome at Cleveland to be erupted and destroyed at Cleveland since July 2011.

Another explosion occurred on April 19 that generated a small ash cloud to 4-6 km. Satellite images taken after the eruption show block and ash deposits extending up to 1 km down the south flank of the volcano. After this explosion, a fourth lava dome began growing within the summit crater; this dome was about 25 m diameter on April 27. This fourth dome was destroyed sometime prior to May 4, in an explosion too small to be detected by the dis-

86

tant infrasound and seismic statiosn. Following that explosion, a fifth dome began extruding, although it was very short lived, and destroyed by small explosions on May 4th or May 5th.

On June 6, Nikolski residents reported a strong sulfur smell, and a low-level plume was observed in web camera images. Satellite images from June 9 and 10 showed deposits of minor amounts of ash, extending as far as 5000 feet from the summit.

On Tuesday June 19, a pilot report, web camera images, and distant infrasound data detected an explosive eruption at Cleveland Volcano. The pilot report estimated the plume height at 35,000 feet. Satellite data suggest that the plume contained a relatively small amount of ash and was similar to other plumes produced

by Cleveland explosions in the past year.

A small lava dome was observed growing in the summit crater

by June 26; and another small explosion was detected by distant infrasound and seismic sensors in the wee hours of June 26.

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On Saturday, August 4, 2012, at 8:38 AM, a small explosive event occurred at Cleveland. This event was detected by retrospective analysis of infrasound data. Satellite images showed a brief, faint steam plume about 4 hours before the event. Another small explosion occurred on Friday, August 17, 2012. This explosion was detected via seismic and infrasound instruments on nearby volcanoes. No ash cloud was observed in satellite imagery. This explosion was the twentieth at Cleveland since December 25, 2011. Another small explosion, this one with low-level ash cloud, occurred at 6:55 AM on August 19. The ash cloud tracked to the southeast and dispersed over several hours.

On September 5, 2012, AVO lowered the aviation color code to YELLOW and the volcano alert level to ADVISORY, based on lack of eruptive activity since August 20. Cleveland remained cloudy for much of the rest of September and October.

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Lava and lahar deposits settling on Mount Cleveland.

Photo Credit to Cyrus Reed.

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On Sunday, November 10, 2012, a small ash cloud from Cleveland was detected in satellite views. Satellite images from 11:47 AM through 6:43 PM show the ash cloud, which was last observed about 60 miles south of Dutch Harbor. In response to this explosion, AVO raised the volcano alert level to WATCH and the aviation color code to ORANGE. AVO lowered the volcano alert level to ADVISORY and the aviation color code to YELLOW on November 21, 2012, based on no further explosions since November 10, 2012, and no evidence of lava dome growth during that time. Elevated surface temperatures persisted during partly or mostly cloudy views through the end of November and the first half of December, 2012.

Elevated surface temperatures were again observed in mid-January, 2013. More consistent high temperatures returned in late January, 2013.

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2010 Eruptions In a May 25, 2010 VAN/VONA, AVO warned “thermal anomalies observed in satellite data over the past few days suggest that Cleveland Volcano has entered another period of volcanic unrest.

In the past, the presence of thermal anomalies at the summit has been followed by moderate ash bursts, sometimes to aircraft flight levels. Therefore, AVO is raising the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY.

“The lack of a real-time seismic network at Cleveland means that AVO is unable to track local earthquake activity related to volcanic unrest. Unrest at Cleveland is frequent, and short-lived explosions with ash clouds or plumes that could exceed 20,000 ft above sea level can occur without warning and may go undetected on satellite imagery.”

On May 31, analysis of satellite imagery from May 30, 2010, re-

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vealed “a small ash emission occurred early last night from Cleveland. The cloud was visible in a 7:56 pm ADT May 30 (0356 UTC, May 31) satellite image moving to the southwest and it did not rise above 16,000’ ASL. At the time of the satellite image, the cloud was detached, and it is estimated that the emission occurred several hours earlier. The event was a short-lived ash emission and there are no signs of further activity.”

Satellite images obtained by AVO on May 31 also showed minor flowage deposits on the upper flank of the volcano. A weak thermal anomaly detected on June 2 suggested continuing low-level ash emission at Cleveland.

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On Sunday, November 10, 2012, a small ash cloud from Cleveland was detected in satellite views. Satellite images from 11:47 AM through 6:43 PM show the ash cloud, which was last observed about 60 miles south of Dutch Harbor. In response to this explosion, AVO raised the volcano alert level to WATCH and the aviation color code to ORANGE. AVO lowered the volcano alert level to ADVISORY and the aviation color code to YELLOW on November 21, 2012, based on no further explosions since November 10, 2012, and no evidence of lava dome growth during that time. Elevated surface temperatures persisted during partly or mostly cloudy views through the end of November and the first half of December, 2012.

Elevated surface temperatures were again observed in mid-January, 2013. More consistent high temperatures returned in late January, 2013.

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OTHER ERUPTIONS

2005 2001 1994 1987

2009 Eruptions

1986 1985 1985 1984

“Satellite data indicate that Cleveland volcano erupted briefly this morning at 07:30 UTC, October 02, 2009, producing an ash

1975 1944 1938 1932

cloud to maximum altitudes of 15,000’ to 20,000’ feet. Thus, the

1897

aviation color code is being increased to Orange, and the volcano

1893

alert level is being increased to Watch.

1828

”

— AVO Volcanic Activity Notice

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culture Mount Cleveland

THE NATIVE ALEUT NAME for Mount Cleveland is Chuginadak (the name currently given to the island as a whole), referring to the Aleut fire goddess, thought to reside in the volcano. The volcano’s name is a reference to its constant activity, and shows that it was likely highly active even in the distant past.

Aleut oral tradition states that, at one time, the western and eastern halves of Chuginadak were separate islands, and that the isthmus joining them was created by volcanic activity sometime in prehistory. The “Islands of Four Mountains” name, the geographic group name for Cleveland and its neighbors, was given to the islands by Russian cartographers in the 19th century. Its current name, Mount Cleveland, was given to it by a U.S. Coast and Geodetic Survey expedition in 1894, when it was originally observed by the USS Concord; like the other volcanoes in the Four Islands group, Mount Cleveland was named after prominent American politicians at the time, Cleveland having been named after then-president Grover Cleveland.

Nikolski (Chalukax in Aleut) is a census-designated place (CDP) on Umnak Island in Aleutians West Census Area, Alaska, United States. The population was 18 at the 2010 census. According to the U.S. Census Bureau, the CDP has a total area of 132.8 square miles, of which, 132.1 square miles of it is land and 0.7

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square miles of it is water.

On a clear day the view from Nikolski is dominated by Mount Vsevidof to the northeast, the highest point on Umnak Island. Mount Cleveland can also be seen from Nikolski, which is the closest inhabitable island to the volcano. The boundary between the Alaska Time Zone and Hawaii-Aleutian Time Zone passes just west of Nikolski, along the line of 169°30’W through Samalga Pass. This places Nikolski in the Alaska Time Zone. However, as Nikolski is part of the Aleutian Region School District the settlement effectively observes Hawaii-Aleutian time.

As of the census of 2000, there were 39 people, 15 households, and 12 families residing in the CDP. The population density was 0.3 people per square mile.

There were 28 housing units at an average density of 0.2/sq mile. The racial makeup of the CDP was 30.77% White and 69.23% Native American. There were 15 households out of which 40.0% had children under the age of 18 living with them, 53.3% were married couples living together, 20.0% had a female householder with no husband present, and 20.0% were non-families. 20.0% of all households were made up of individuals and none had someone living alone who was 65 years of age or older. The average household size was 2.60 and the average family size was 2.92.

In the CDP the population was spread out with 35.9% under the age of 18, 30.8% from 25 to 44, 23.1% from 45 to 64, and 10.3% who were 65 years of age or older.

The median age was 40 years. For every 100 females there were 105.3 males. For 96

every 100 females age 18 and over, there were 92.3 males.

The median income for a household in the CDP was $38,750, and the median income for a family was $40,250. Males had a median income of $26,250 versus $11,875 for females. The per capita income for the CDP was $14,083. There were 23.5% of families and 20.7% of the population living below the poverty line, including 13.6% of under eighteens and 55.6% of those over 64.

Nikolski is reputed by some to be the oldest continuously-occupied community in the world. People have been living in Nikolski for at least 8,000 years, before the pyramids were built, the Mayan calendar was invented, or the Chinese language was written.

In 1834, it was the site of sea otter hunting, and was recorded by the Russians as “Recheshnoe,” which means “river.” In 1920, a boom in fox farming occurred here. The Unangan became affluent enough to purchase a relatively large boat, the “Umnak Native,” which was wrecked in 1933. A sheep ranch was established in 1926 as part of the Aleutian Livestock Company. There are still a few sheep, some fencing remnants and a barn left over as the remnants of this Sheep Ranch.In June 1942, when the Japanese attacked Unalaska and seized Attu and Kiska, residents were evacuated to the Ketchikan area. Locals were allowed to return in 1944, but the exposure to the outside world brought about many changes in the traditional lifestyle and community attitudes. In the 1950s, the Air Force constructed a White Alice radar communication site here, which provided some jobs.

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Ashfall falling on Lady Gudny, off the coast of Nikolski. Photo credit to Anne Hillman.

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Photo Credit Game McGimsely

The base of Mt. Cleveland. Opposite: Geologist Cyrus Reed walks on the base.

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Photo Credit Chad Hults.

Steam rising from Mount Cleveland’s Summit

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Bob Webster

Eruption plume in 2012 through clouds looking at Mount Cleveland.

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Mount Veniaminof

Elevation:

8225 ft

Latitude:

56.1979째 N

Longitude:

159.3931째 W

Veniaminof Volcano is one the highest of Alaska.

Official Name: Veniaminof Type: Stratovolcano Latest Activity: 2002

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ty p e :

MOUNT VENIAMINOF IS a broad central mountain, 35 km wide at the base,

truncated by a spectacular steep-walled summit caldera 8x11 km in diameter.

The caldera is filled by an ice field that ranges in elevation from approximately 1750 to 2000 m; ice obscures the south rim of the caldera and covers 220 square km of the south flank of the volcano. Alpine glaciers descend from the caldera through gaps on the west and north sides of the rim and other alpine glaciers occupy valleys on the north-, east-, and west-facing slopes of the mountain. In the western part of the caldera, an active intracaldera cone with a small summit crater has an elevation of 2156 m, approximately 330 m above the surrounding ice field. The rim of a larger but more subdued intracaldera cone protrudes just above the ice surface in the northern part of the caldera; based on limited exposure and physiographic features, it may have a summit crater as much as 2.5 km in diameter.

Andesitic and dacitic ash-flow tuffs from the caldera-forming eruption occur

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in many of the valleys on the north slope of the volcano and are found as far away as 31 miles from the caldera rim on both the Bering Sea and Pacific Ocean coasts.

A northwest-trending belt of post-caldera cinder and scoria cones, including the two intracaldera cones, extends from near the Bering Sea coast approximately 55 km across the main volcanic edifice and the Aleutian Range divide, well down the Pacific slope.

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eruptions and activity start date: 09.28.2002 stop date: 03.23.2003

Perryville residents next reported ‘plumes of smoke’ between 8 and 10 pm on

volcanic explosivity (VEI): 1 eruptive characteristics: Tephra Plume

October 1. Others reported ‘rumbling’ during the evening, however no clearly correlative signals were noted on seismograms. One and one half minutes of video taken on October 2 or 3, about 2 pm, from the vantage of the Sandy River 28 miles west of the active cone showed several small, dilute, gray-brown clouds rising about 300-600 ft above the intracaldera cone and drifting a short distance to the north. In the 1.5 minutes of tape, two distinct ‘puffs’, about 1 minute apart, rise from the cone and drift downwind. The cone was not unusually snow free, however, a dark covering of ash was visible on the caldera ice field at the base of the cone and extending generally north. On October 6, Sandy River Lodge reported black ash and ‘smoke’ rising 400-500 ft above the cone, explosions, and ground shaking.

“Cloud-free satellite images of the Veniaminof caldera revealed nothing unusual until October 2 when AVO acquired a Moderate Resolution Imaging Spectroradiometer image that captured a localized, gray deposit on the caldera ice field.

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The image shows a faint, fan-shaped deposit extending generally east from the cone to the caldera boundary and perhaps just beyond. When viewed in light of reports from Perryville and the video from Sandy River, the dark fan likely represents ash fall from low-level phreatic activity on October 1. No thermal anomalies were detected in satellite imagery throughout this period and no incandescence was reported. A compilation of reports from residents and other observers through the end of the year is presented in table 3. Seismicity and reports of discolored clouds over the intracaldera cone gradually declined through the fall.

A re-invigorated hydrothermal system beneath the intracaldera cone may account for these intermittent ejections of diffuse, ash-bearing clouds. It seems unlikely that this was prompted by a new magmatic intrusion at depth based on the lack of volcano-tectonic earthquakes. Increased hydrothermal activity may have been related to what was, according to some long time residents of the area, one of the rainiest autumns in memory. Although precipitation falling at the elevation of the intracaldera cone would have been in the form of snow, precipitation in Cold Bay was approximately 80% above normal for the month

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of October, according to long term climate records maintained by NW (National Oceanic and Atmospheric Administration.

start date: 04.17.1995 stop date: 11.30.1996 volcanic explosivity (VEI): 1 eruptive characteristics: Tephra Plume Central Eruption

In mid-April, 1995, reports from observers in Perryville and Port Heiden of small dark plumes over Veniaminof coincided with thermal anomalies near the active vent recorded on satellite images. This low-level activity was interpreted to result from interaction of lava with ice and snow causing occasional low-energy ash bursts and steam generation. Perryville residents heard rumblings and booms and witnessed minor ash emission on November 15, 1995, as reported in the last AVO weekly update that included Veniaminof (12-1-95). Summit hot spots were visible on satellite images of November 2, 8, and 17, 1995.

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start date: 07.30.1993 stop date: 08.28.1994

Reports of activity at Veniaminof began in early 1993. Pilots reported a steam

volcanic explosivity (VEI): 2

plume rising from the volcano on February 18, 1993. Confirmed magmatic ac-

eruptive characteristics:

tivity was first sighted on July 30, 1993. Observers in Perryville reported black

Tephra Plume

clouds rising over the summit beginning at 1430 ADT on July 30, 1993. A white

Central Eruption

steam cloud was present at other times. A small eruption plume was observed Subglacia

on satellite imagery by the NW on July 30, but none were seen in the following days. On the morning of July 31, Perryville observers saw a gray cloud rising from the volcano and extending to the south. On August 2, commercial airline pilots observed intermittent venting of black ash clouds rising nearly 1,000 feet above the active intracaldera cone. On August 3, U.S. Fish and Wildlife (USFWS) personnel reported a steaming pit in the snow at base of the west side of the intracaldera cinder cone. Pilot reports on August 3 described black ash and bombs erupting from the summit vent of the intracaldera cone at 30-60 second intervals to a height of 7,900-9,800 ft above sea level 82,756 ft] above vent. A minor dusting of very fine ash occurred in Port Heiden after 2000 ADT on August 3, 1993. Residents of Perryville, Chignik, and Chignik Lake also heard a “rumbling noise� accompanied by a slight tremor at about 2200 that night.

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Flight restrictions around Veniaminof were put into effect August 4, 1993. On the morning of August 6, a resident of Port Heiden observed eruptions of ash and steam at 3-4 minute intervals; these plumes barely rose above the summit of the volcano. There were no reports of ashfall at other nearby villages. On August 12, a pilot reported ash venting 600-900 m (1,900 - 3,000 ft) above the crater with the ash cloud carried east-northeast.

Poor weather precluded many observations during the fall. On October 1-2, residents of Port Heiden observed steam and ash emissions over Veniaminof. An Advanced Very High Resolution Radiometer (AVHRR) image from the late morning of October 2 – the first clear satellite image in almost two months – showed a faint northeast-directed plume and a thermal anomaly at the summit cinder cone. During the night of October 7, residents of Perryville observed bursts of incandescent material rising approximately 1,000 ft above the summit. These bursts occurred about once every 10 minutes, were accompanied by loud rumbling sounds, and appeared to be similar in size to the eruptions in July and August. On October 14, residents of Perryville observed continued emis-

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sion of a gray, steam and ash plume rising about 3,280 ft above the summit.

Though the summit was obscured by haze on October 22, observations from Perryville indicated a decrease in the level of activity relative to that earlier in the month. Activity continued intermittently for the remainder of 1993. During favorable wind and weather conditions, Port Heiden residents noted dark ash clouds above the volcano and deep rumbling was reported by residents in Port Heiden and Perryville.

start date: 11.29.1984

Eruptive activity resumed on 29 November 1984. Perryville residents were awak-

stop date: 12.09.1984 volcanic explosivity (VEI): 2 eruptive characteristics: Tephra Plume Central Eruption

ened by rumbling noises from the volcano. By 0800, a black ash cloud was rising to about 3.5-4 km altitude. At 1000, a second plume rose to about 4 km, followed by smaller bursts that were occurring at approximately 5-minute intervals as of about 1020. Pilots reported an ash plume to about 4.5 km altitude at 1045, very little activity at 1100, and another ash plume to about 5.4 km at 1115. No incandescent material was observed from Perryville or by the pilots.

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OTHER ERUPTIONS

1983 1956 1944 1939 1930

A pilot who flew over the volcano on the morning of 5 December reported a white vapor plume, containing only a small amount of ash, rising from two small pits on the E side of the previously active cone. One of the pits was steaming more vigorously than the other, and a brownish haze drifted downwind from the volcano. He observed no incandescent material or recent lava extrusions.

On 6 December, Perryville residents observed large vapor plumes of varying intensity that contained very minor amounts of ash. They saw no incandescent material, and had heard no rumbling noises during the previous several days.

On 7-8 December the volcano was obscured by weather clouds; however, small intermittent vapor plumes with no ash were observed from Perryville on the 9th.

No incandescent material was seen. On the 10th and 11th, the volcano was not visible from Perryville.

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1892 1874 1830

culture Veniaminof

Perryville and Ivanof Bay are the closest towns closest to Veniaminof Volcano.

They are within 25 miles of the volcano. Perryville is located within the Lake and Peninsula Borough in Alaska. As of the census of 2000, there were 107 people, 33 households, and 23 families residing in the Census Designated Place (CDP). The population density was 11.6 people per square mile. There were 45 housing units at an average density of

/sq mi. The racial makeup of the CDP

4.9

was 1.87% White, 97.20% Native American, and 0.93% from two or more races. There were 33 households out of which 51.5% had children under the age of 18 living with them, 45.5% were married couples living together, 18.2% had a female householder with no husband present, and 30.3% were non-families.

27.3% of all households were made up of individuals and 3.0% had someone living alone who was 65 years of age or older. In Ivanof Bay, there were 22 people, 9 households, and 7 families residing in the CDP. The population density was 6.5 people per square mile. There were 12 housing units at an average density of 3.6 per square mile. The racial makeup of the CDP was 4.55% White

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and 95.45% Native American.

There were 9 households out of which 22.2% had children under the age of 18 living with them, 33.3% were married couples living together, and 22.2% were non-families. The main forms of employment on Perryville is fishing, mainly for crabs.

Photo Credit.USGS

Ivanof Bay is one of the closest inhabitable islands next to Veniaminof

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Photo Credit.USGS

Perryville beach looking towards the volcano.

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Photo Credit Tim Plucinski.

Steam emitting from the intercaldera

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Photo Credit Game McGimsely

Veniaminof’s lava flow

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Photo Credit Game McGimsely

Steaming cinder in 1984

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Beautiful lava formation on Perryville Beach. Photo Credit to Cyrus Reed.

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vulcan vulcan is a resource that provides information about volcanoes in america. this edition of vulcan focuses on the most active volcanoes in alaska. the information provided is from alaska volcano observatory and the united states geological services.

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