GEOGRAPHY
KYUSHU
Field Trip Report on Mount Aso Date: 16/7/2010 Time: 14:00 – 15:30 Venue: Mountain Aso Weather condition: Windy with showers Objectives: 1) To study the relief and rock characteristics of Aso caldera 2) To understand the warning system set up by Japan Reporters: Yau Chak Lam (4B) Cheung Yik Chi (3C) Chan Lai Yee (3D) Chiu Yim Wa (3D)
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Background 1. Formation of Mount Aso
Before discussing the formation of Aso caldera, it is really important to understand the formation of Mountain Aso. Frankly speaking, Japan is a volcanic island arc and it is near to the boundary of the Eurasian Plate, the Philippine Plate and the Pacific Plate. Due to the converging convection cells of magma in the asthenosphere, the oceanic crust of Eurasian Plate collides with the Philippine Plate which is an oceanic plate. The edge of the Philippine Plate sinks beneath the edge of the Eurasian Plate and subduction occurs. The edge of the oceanic plate subducts into the asthenosphere and it melts. Line of weakness or crack is produced. There is a release of pressure and magma rises up through the crack. When reaching the surface, lava piles up around the vent (i.e. opening at the Earth’s surface), cools and solidifies to form a volcano. Since the volcano is found below the sea level, we always call it a submarine volcano. After a number of eruptions, it may rise above sea level to become a volcano on the ground. In this case, the Mount Aso is formed. CCSC Geography
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2. Formation of Aso caldera
Aso caldera is 24 km wide and it is one of the largest caldera in the world. It is believed that the caldera was created by four particularly great eruptions long time ago. As these volcanic eruptions were extremely violent, the magma chamber underground became emptied and it is unable to support the weight of the volcano. As a consequence, there will be a subsidence of the upper part of the volcano and the crater is destroyed. The caldera is then formed. Observation When traveling to Mount Aso by ropeway, we discover that there are some igneous rocks covered by vegetation and joints are obvious. Also, there are milky solutions between the rocks and they are probably the mixture of water and some minerals.
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Since there have been no violent volcanic eruptions for a long time, it is likely no volcanic ash are ejected to the area. In this case, vegetation is able to grow on rocks.
Besides being an observation area, the most surprising thing is that it is an evacuation area!
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A caldera is always a deep and concave depression. The cliff beside it is so steep and mountainous and it should be a part of the original volcano. Before those violent volcanic eruptions, the volcano should own a great height. A caldera is formed here and there are some light yellow solutions. We believe that rainwater is mixed with sulphur and it forms a mini size of crater lake! Next to the crater lake, there is some fine-grained “sand� with black colour. They are volcanic ash ejected during catastrophic eruptions. Moreover, there are some brown materials beside it. In fact, they are ash mixed with rainwater. Mudflows are formed when severe rainstorms occur. When it stops raining, the velocity of mudflow will gradually become smaller. It finally stops and deposits. Finally, they become more vicious and the colour
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The ground is covered by a large amount of volcanic ash. We can imagine how violent the eruption is!
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There is some steam coming from the caldera. Since the boiling point of sulphur is approximately 446째C, the temperature of the caldera should be much higher than this and thus we strongly believe that it is steam form of sulphur.
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Conclusion After the trip, we find out that some parts of volcanoes can consist of soils. When rocks are weathered, they will gradually disintegrate into soil. Nevertheless, slopes composed of soil are never safe. Consequently, the council makes use of supporting materials to strengthen the weak zone. Also, we discover that volcanoes seldom occur violent eruptions. We always have a wrong perception that volcanoes often erupt. It is never true and active volcanoes will only continually eject a trace amount of volcanic materials. Other two types of volcanoes – dormant volcanoes and extinct volcanoes will have fewer chances for violent eruptions to occur. To conclude, volcano is always a two-edged sword. Not only it can provide fertile soils for farmer and promote ecotourism, it may also erupt and cause losses of lives and property. Since the Mount Aso is still an active volcano and it may explode fiercely in the future, citizens in Japan should still keep our alerts on it and obtain information from the observatory so as to protect their safety!
Acknowledgement Figure 4 taken from 4B Po Ting Hei Figure 2, 3, 5and 7 taken from 4C Hau Yat Long Figure 6, 8, 9 taken from Mr. Lui Thanks Popo, Sunny Hau and Mr. Lui for providing photos and making the report so fruitful!
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Study on rivers Takachiho Gorge
Takachiho(Gorge((Takachiho.kyo)(is(a(narrow(chasm(cut(through(the(rock(by(the(Gokase( River.(The(nearly(sheer(cliffs(lining(the(gorge(are(made(of(slow(forming(volcanic(basalt( columns(which(resemble(the(scales(of(a(dragon(where(the(stone(twisted(and(>lowed(as(it( formed.(It(is(located(at(the(upper(course(of(the(river.(Different(>luvial(features(can(be(seen( here.
What%are%the%General%Characteris(cs)of)the)Upper)Course)of)Rivers?)
Generally,)the)upper)course)of)rivers)has)a)low)discharge)with)a)rela7vely)lower) mean)velocity)compared)with)the)other)parts)of)the)river.)Due)to)the)above)facts,) the)eect)of)down=cu>ng)(lateral)erosion))and)headward=erosion)is)dominant.)This) is)probably)because)the)river)water)is)of)a)lower)quan7ty)and)it)works)generally)on) the)riverbed.)Without)abundant)energy,)larger)rocks)can)be)found)along)the)course.) Common)uvial)features)found)included)waterfalls,)rapids,)potholes)and)Deep=V) shaped)Gorge.)The)speciďŹ c)forma7ons)of)these)features)are)demonstrated)as) follows:
Waterfalls)and)plunge)pools They%are)ver)cal%flow%of%rivers%due%to%a% steep%break%of%slope%due%to%faul)ng%or%the% difference%in%resistance%of%rocks.
Potholes They%are%hollows%on%the%river%bed. When%river%water%flows%through%uneven% surface,%turbulences%and%vor)ces%will%be% produced.%The%water%(through%hydraulic% ac)on)%and%load%(through%Abrasion),%aAer%a% long%)me,%would%drill%holes%on%the%river%bed.% At%dry%seasons%or%with%changes%in%landscape,% they%may%be%exposed%and%become%visible.
Rapids They%are%formed%when%there%is%uneven%surface%caused%by%dierent%resistance%of%rocks%and% dierent%severity%of%erosion.
Now,%it%is%)me%for%what%we%can%see%in%the% real%river.%%In%the%following%picture,%we%can% ! see%that%the%river%gorge%is%very%deep%though% the%VGshape%is%not%so%obvious.%%
! Rapids%can%be%seen%in%places%with% excep)onally%rough%river%channel%due%to% different%resistance%of%rocks.%Vor)ces%and% turbulence%are%produced.%
The%waterfall%refers%to%a%sudden%depression% of%land%and%a%ver)cal%flow%of%river.%The%water% velocity%at%then%is%very%high.% !
! Corrasion%(sandGpaper%effect)%is%very%much% observed%in%the%following%place%where%these% circular%hollows%called%potholes%are%drilled%by% rocks.%Mean%velocity%remained%low.
What%we%learnt%during%geography%lessons%is%very%different%from%what%we%had%seen%at%Takachiho% Gorge.%The%Takachiho%Gorge%is%smaller%than%what%we%had%expected.%It%is%far%smaller%than%the%Grand% Canyon%and%the%Three%Gorges,%which%I%always%thought%that%a%gorge%should%be%very%spectacular.% Another%thing%we%could%see%was%that%the%velocity%of%the%river%is%quite%high,%especially%that%going% through%rapids%and%the%waterfall.%However,%we%learnt%that%the%velocity%at%the%upper%course%of%the% river%is%the%lowest,%and%it%is%contradictory.%Actually,%we%are%talking%about%the%average%(mean)% velocity%is%the%lowest%at%the%upper%course%but%not%the%par)al%water%speed%we%observed%there. %The%most%surprising%thing%is%the%size%of%the%waterfall!%Most%people%think%that%waterfalls%should%be% very%grand%and%impressive%and%they%do%not%except%a%small%scale%waterfall.%Honestly%speaking,%the% waterfall%we%saw%at%Takachiho%Gorge%is%quite%small%in%scale.%Some%students%thought%that%a% waterfall%is%on%the%main%stream.%However,%the%Takachiho%Waterfall%is%just%the%confluence%of%the% tributary%and%the%main%stream,%and%this%is%not%men)oned%in%our%textbook.% The%main%difference%we%found%is%that%the%geographical%features%are%not%as%obvious%as%the% illustra)on%on%the%notes.%In%the%natural%Takachiho%Gorge,%the%geographical%features,%like%potholes% and%the%fault,%are%hidden%by%vegeta)on%cover%and%other%erosion%works%such%as%hydraulic%ac)on%and% abrasion%make%them%become%uneasy%to%observe.
Any$other$special$features$we$can$find? Faul)ng Along%the%gorge,%we%can%observe%a%number%of% cliffs.%The%cliffs%are%actually%formed%by%faul)ng.% Due%to%tectonic%ac)vi)es,%land%was%upliAed%and% a%plane%appeared%aAer%the%ver)cal% displacement.%The%cliff%was%thus%formed.%Rocks% were%also%shown%on%the%plane. Hexagonal%Basalt On%the%cliff,%we%can%observe%that%rocks%are% hexagonal%in%shape.%They%are%black%in%colour,% fine%grained%and%with%columnar%joints.%Some%of% them%are%being%bent%and%placed%horizontally.% The%rocks%are%known%as%basalt%which%is%a%kind%of% basic%extrusive%rocks,%formed%by%lava%that% flowed%out%during%erup)on%of%AsoGsan.%The% special%hexagonal%basalt%was%formed%by%faul)ng% inside%the%caldera.%Due%to%tectonic%forces,% hexagonal%rocks%are%compressed%or%displaced% and%formed%the%outcrop%we%can%see%today.
What$can$we$learn? We%found%that%going%out%to%have%a%look%is%really%a%must%in%studying%Geography.%Those%theories%we% learnt%in%the%books%are%some)mes%dierent%from%what%we%can%see%in%the%reality.%We%should%not% just%lock%ourselves%in%the%rooms%and%sit%in%front%of%the%computers%to%expect%that%new%knowledge% will%be%found%on%our%desks%directly.%We%should%not%study%the%books%blindly%without%disgus)ng%the% meanings%of%the%words%but%try%to%explore%the%new%things.%Experiences%are%always%more% momentous%than%theories.% %%Moreover,%we%found%that%nature%is%so%fabulous%that%we%should%go%out%more!%Many%people%are% afraid%of%the%hot%summers%and%they%prefer%to%stay%at%home.%We%suggest%you%to%go%in%tough%with%the% nature%when%you%have%)me%but%not%just%siXng%in%front%of%the%computers%all%the%day!
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