Glacial Flooding & Disaster Risk Management Knowledge Exchange and Field Training July 11-24, 2013 in Huaraz, Peru HighMountains.org/workshop/peru-2013
Comparison of recently formed glacial lakes in the Bolivian Andes and the Southern Alps of New Zealand -‐ Differences and similarities Dirk Hoffman Bolivian Mountain Institute – BMI Email: dirk.hoffmann@bolivian-mountains.org
Abstract As mountain glaciers recede, there is the potential for the formation of glacial lakes, depending on the conditions of the terrain as well as the characteristics of the moraines. These newly formed glacial lakes have been recognized in high mountain regions around the world as posing a considerable risk. In the Bolivian Andes glacial lakes have not yet received much attention, neither by the local population nor by researchers. A first documented case of a GLOF (Glacial Lake Outburst Flood), which in November 2009 destroyed numerous fields, various kilometers of a rural road and killed some farm animals has made it clear that Bolivian glacial lakes – even though relatively small in size -‐ are potentially dangerous. In New Zealand’s Southern Alps, glacial lakes are not as numerous, but larger in size. They can be found most prominently on the lower parts of the tongues of the 12 long valley glaciers. There is, however, no known case of a glacial lake outburst flood, and lakes are widely considered as not being dangerous. This paper explores the differences and similarities of recently formed glacial lakes in the Bolivian Andes and those in the Southern Alps of New Zealand, focussing especially on the risks associated, and management options resulting thereof. Key words Glacial lakes, climate change, glacial retreat, Bolivia, New Zealand, Andes, Southern Alps
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Introduction Wherever mountain glaciers recede, there is the potential for the formation of glacial lakes, depending on the conditions of the terrain as well as the characteristics of the moraines. These newly formed lakes often pose a considerable risk to human settlements and infrastructure downstream, which is not always recognized and managed adequately. In January and February of this year, I undertook a climate change study tour to New Zealand, organized with the Bolivian Mountain Institute – BMI. One objective had been to investigate how climate change impacted the Southern Alps of New Zealand, and to gain insides into how potentially dangerous glacial lakes were managed. – I was in for a surprise. Glacier retreat and glacial lakes in Bolivia Climate change is a reality in the Bolivian Andes. Temperature, precipitation and humidity have changed considerably over the last 50 years. Temperature increase has been about 0.3° C per decade at the end of the 20th century. Bolivia is home to around 20% of the world’s tropical glaciers, with Peru holding about 70%, Ecuador and Columbia combined 4%, and the rest of the world less than 1%. As in most regions of the world, accelerated melting of glaciers set in around 1980. At this time Bolivia held 566 km² of glacier area in its cordilleras. Due to global warming, Bolivia’s tropical glaciers are retreating at an unprecedented rate. Recent investigations of glacial recession indicate that glacier surface and area have been reduced by about 50% during the last 35 years (Soruco et al. 2009). Hundreds of glacial lakes have subsequently formed at the tip of the tongue of the glaciers, which might grow to considerable size depending on local terrain conditions. These glacial lakes are often dammed by moraines made up of loose material that might yield to the pressure of the water and break, releasing enormous amounts of water downstream. In the Bolivian Andes glacial lakes have not yet received much attention, neither by the local population nor by researchers. The recent glacial lake inventory and preliminary risk assessment realized in 2011 by Daniel Weggenmann for the Apolobamba mountain range is the first work of its kind (an inventory for the Cordillera Real is presently being prepared by other researchers). The results of the Apolobamba glacier lake inventory show that the total number of contemporary glacial lakes went up from 174 to 216 in the period from 1986-‐2008, while total lake area grew by approximately 2.5 km² (Weggenmann, 2011).
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Graphic 1: The ice-‐dammed glacial lake above Keara before its outbreak (left; Google Earth image, 2005) and as seen today (right; photo by author, May 2013). The first and only documented GLOF incident in Bolivia took place on November 3, 2009 in the village of Keara in the Northern part of the Apolobamba mountain range, causing damage to the local road, a bridge, killing farm animals, invading fields and eroding the river banks; fortunately not causing any human casualties. This incident, together with the glacial lake inventory and the efforts of individuals from NGOs and UMSA state university, helped to include glaciers and glacial lakes into the Social Monitoring Program adopted by Apolobamba Protected Area in 2012. Glacier retreat and glacial lakes in New Zealand New Zealand’s glaciers are almost exclusively located in the Southern Alps of its South Island, covering an area of approximately 1,160 km². One of the particularities of the Southern Alps consists in the extremely high rate of mountain uplift of around 10 mm/yr, due to plate movements. This figure is more than double than for other major mountain ranges. Because of the moderating effect of the huge water mass of the Pacific Ocean surrounding New Zealand, global warming is less pronounced than in other mountain ranges within large continental masses. Temperature rise for the Southern Alps has been calculated to be around 1° C (by 1979), largely after the 1950s, which at present should stand between 1.5 – 2 °C. This has led to the retreat of New Zealand glaciers, even though not always in synchrony with the retreat patterns predominating globally. “Wholesale retreat of New Zealand glaciers over most of the 20th century is generally attributed to regional warming (...). However, there have been reversals within this overall recession from glacier retreat to glacier advance. These have sometimes been related to regional precipitation increases”, writes Trevor Chinn, New Zealand’s foremost glacier expert (Chinn et al. 2012). Total ice loss volume has been calculated from 54.53 km³ in 1976 to 46.12 km³ in 2008, which equals about 15%. Up to now, glacial lakes have only formed on the 12 large valley glaciers, characterized by low-‐gradients and extensive debris cover. Those remained their areal extent until the 70s, even though notable down-‐wasting took place. Because of their slow response time, these long glaciers filter out more of
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regional climate as compared to the overall warming of the atmosphere across New Zealand.
Hooker and Mueller lakes (left); alluvial gravel fan below Mueller glacier (right); photos by author. Mainly during the 1980s the formation of small supra-‐glacial ponds set in, which quickly lead to the formation of glacial lakes. What followed during the 1990s was the rapid expansion of these lakes, which for the respective glaciers marked “a tipping point once rapid frontal retreat is initiated by lake growth” (Chinn et al. 2012). This feedback mechanism has started a new dynamic of accelerated lake expansion and accelerated melting of the glacier tongue, which is now under way. It is important to notice, however, that these glacial lakes are dammed by alluvial outwash gravel plains, and not by brittle moraines, which makes them much more stable. It is for this reason, that existing glacial lakes are not considered dangerous, but as a tourist attraction. Research is mainly directed to understand lake building and expansion processes, as well as calculating the impact glacial lakes have on the rate of glacial recession at the tongues that are in contact with lake water. Similarities The similarities between glacial lakes in Bolivian and New Zealand high mountain regions can be resumed the following way: •
There is a clear trend of glacial recession in both regions, largely in line with worldwide trends of glacial retreat.
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In both cases, a number of glacial lakes have formed over the last decades at the snouts of glaciers.
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These lakes have notably, sometimes dramatically increased in size.
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Formation of glacial lakes is an ongoing phenomenon.
Differences
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Differences between glacial lakes of the New Zealand Southern Alps and the Bolivian Andes are numerous; they can be summarized as follows: •
Ice loss in Bolivia (45-‐50%) over the last 40 years was about three times that of New Zealand (15%).
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Glacial lakes in Bolivia are more numerous (a few hundred compared to 12).
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Glacial lakes in New Zealand are much larger in size and water volume.
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Some of the lakes in Bolivia are to be considered dangerous; there was a first recorded GLOF incident in 2009.
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New Zealand’s recently formed lakes are considered not to pose any danger, they are even used as a new tourist attraction.
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Besides traditional settlements in glacierized watersheds, in Bolivia there are mining and agricultural activities taking place close to glaciers.
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In New Zealand there is no native population in high mountain areas; in certain places touristic infrastructure is present.
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Differences in mountain geo-‐morphology and topography are important: -‐ long valley glaciers in New Zealand (absent in Bolivia); -‐ very high rates of uplift in the Southern Alps: 10 mm/yr; -‐ lake levels in New Zealand are lowering over time; -‐ alluvial outwash gravel plains instead of moraine dams
Drawing showing the formation of large alluvial outwash plains at the heads of modern day glaciers and glacial lakes in New Zealand; source: Chinn Conclusions Contrary to my initial expectations, differences are more significant than similarities when comparing glacial lakes in the Bolivian Andes and New Zealand’s Southern Alps.
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They are based mainly on the geo-‐morphological characteristics of the mountain ranges and its glaciers. In Bolivia, there is a need to realize glacial lake inventories of other mountain regions, especially Cordillera Real, expand monitoring activities, and to realize on-‐site technical expert surveys of those glacial lakes identified as possibly dangerous. In New Zealand, in contrast, there is presently no need for management of glacial lakes. It might be good, however, to analyze the possibility of rock avalanches falling into glacier lakes, as well as to take another close look at topography higher up to make sure no dangerous glacial lakes would form there in the future. Acknowledgements I would like to thank Daniel Weggenmann, Rodrigo Tarquino, Apolobamba National Park, Stefan Winkler, Trevor Chinn, the participants of the annual Snow & Ice Research Group (SIRG) meeting, and many others for their contribution to this work and the time dedicated to discuss the situation of glacial lakes in the Bolivian Andes and the New Zealand Southern Alps. It is my wish that in the future some more intense cooperation might result from this first comparative exploration. References Chinn, T. (1996): New Zealand glacier responses to climate change of the past century. New Zealand Journal of Geology and Geophysics, 39:3. Chinn, T., S. Winkler, M.J. Salinger and N. Haakensen (2005): Recent glacier advances in Norway and New Zealand: A comparison of their glaciological and meteorological causes, Geografiska Annaler 87 A. Chin, T., B.B. Fitzharris, A. Willsman and M.J. Salinger (2012): Annual ice volume changes 1976-‐2008 for the New Zealand Southern Alps. Global and Planetary Change 92-‐93. Dykes, R.C., M.S. Brook and S. Winkler (2010): The contemporary retreat of Tasman Glacier, Southern Alps, New Zealand, and the evolution of Tasman proglacial lake since AD 2000. Erdkunde, Vol. 64, No. 2. Haeberli, W., J.J. Clague, C. Huggel and A. Kääb (2010): Hazards from lakes in high-‐ mountain glacier and permafrost regions: climate change effects and process interactions. XI Reunión Nacional de Geomorfología, Solsona, España. Hoffmann, D. (2011): Participatory Glacier Lake Monitoring in Apolobamba Protected Area. A Bolivian Experience. Journal for Sustainability Education, March 19, 2011. Hoffmann, D. & Weggenmann, D. (2013). Climate Change Induced Glacier Retreat and Risk Management: Glacial Lake Outburst Floods (GLOFs) in the Apolobamba Mountain Range. In: Leal Filho, W. (Ed.): Climate Change and Disaster Risk Management, Springer.
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Huggel, C. (2004). Assessment of glacial hazards based on remote sensing and GIS modeling, Zürich, Univ. Geographisches Institut. Jordan, E. (1991). Die Gletscher der bolivianischen Anden eine photogrammetrisch-‐ kartographische Bestandsaufnahme der Gletscher Boliviens als Grundlage für klimatische Deutungen und Potential für die wirtschaftliche Nutzung; mit 34 Tabellen von Ekkehard Jordan, Stuttgart, Steiner. Rabatel, A. et al. (2013). Current state of glaciers in the tropical Andes: a multi-‐century perspective on glacier evolution and climate change. The Cryosphere, 7, 81-‐102. Soruco, A., Vincent, C., Francou, B. & Gonzalez, J. F. (2009). Glacier decline between 1963 and 2006 in the Cordillera Real, Bolivia. Geophysical Research Letters, 36. Weggenmann, D. (2011). Gletscherseeausbrüche in der Cordillera Apolobamba (Bolivien) – Analyse und Bewertung des Risikopotentials im Rahmen des Klimawandels. Diploma (unpublished), Heidelberg University. Winkler, S., Chinn, T, Gartner-‐Roer, I., Nussbaumer, S.U., Zemp, M. and Zumbühl, H.J. (2010). An Introduction to Mountain Glaciers as Climate Indicators with Spatial and Temporal Diversity. Erdkunde, Vol. 64, No. 2. Salinger, J., T. Chinn, A. Willsman and B. Fitzharris (2008). Glacier response to climate change. Water & Atomosphere 16 (3).
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