University of East Anglia
Glacial
Lake Outburst
Flooding in the Himalayas : Implications and
Strategies
Significance of
GLOF in Societal and Scientific Terms
A Technical Review
of Glacial Lakes and Glacial Lake Outburst Floods
Introduction and Background
The aim of this report is to outline the current
scientific understanding and research into the phenomenon known as glacial lake
outburst flooding (GLOF), an issue that has come about as a result of recent
changes to the global climate.
Climate change, particularly the observed warming trend
observed during the latter thirty years of the 20th century is having huge
impacts on many of the world’s dynamical systems. Nowhere has this warming been noticed more
than at areas of high latitude and high altitude, where the changes are thought
to be occurring more rapidly than anywhere else on the planet [1]
(see Figure 1).
Figure 1:
Inter-annual variation in Mean Temperature at
With few exceptions, this has led to many of the world’s
glaciers melting and retreating at an alarming rate, in the Himalayan regions
this process has been particularly well-observed. The Khumbu Glacier in eastern
The
release of this extra water creates two significant problems. The
Significance of GLOF in
Societal and Scientific Terms
Glacial flood events have already caused many deaths and a
tremendous amount of damage in mountainous regions worldwide [5]. The focus here though is primarily in regard
to
Figure 2: Potentially dangerous glacial
lakes of
|
Date |
Name
of |
River
Basin |
|
450
years ago |
|
Seti
Khola |
|
August
1935 |
|
Sun
Koshi |
|
21
September 1964 |
|
Arun |
|
1964 |
|
Sun
Koshi |
|
1964 |
|
Trishuli |
|
1968 |
|
Arun |
|
1969 |
|
Arun |
|
1970 |
|
Arun |
|
3
September 1977 |
|
Dudh
Koshi |
|
23
June 1980 |
|
Tamur |
|
11
July 1981 |
|
Sun
Koshi |
|
27
August 1982 |
|
Arun |
|
4 August
1985 |
Dig |
Dudh
Koshi |
|
12
July 1991 |
|
Tamo
Koshi |
|
3
September 1998 |
|
Dudh
Koshi |
Table
1: Fifteen selected GLOF events recorded in
(Source:
WWF, 2005)
One of the most well-known and documented events occurred
on the 4 August 1985 when the Dig Tsho glacial lake in the Langmoche valley of
eastern Nepal broke through its 50 m bank of ice and terminal moraine. The flood water rose between 10 to 15 metres
high, and the effects were felt more than 90 kilometres downstream [9]
(see Figure 3).
Figure 3: Dig Tsho glacial lake (centre
left), Langmoche Khola and Bhote Koshi (Source: Google Earth)
Many
scientific studies have already assessed various facets of the processes
involved in the development of glacial lakes and outburst flood events. One of the motivations is that it would
appear that the changes in glacier mass‑balance are intrinsically linked
to anthropogenic forcing of the global climate.
It has been suggested by Shrestha (1999) that the Himalayan regions of
Much of the vitally important current work is concerned
with attempting to understand the reasons why some lakes fail whilst others
remain stable. In essence, this is
concerned principally with understanding glacial mechanics and the movement of
debris, through the use of modelling techniques (Huggel et al., 2003).
Glacial lakes appear to become dangerous for a number of
key reasons. Clearly the size and type
of moraine dam is important [10]. However, other important factors include the
presence of a potential catalyst to weaken the dam such as rock falls,
mass-movements or avalanche material, or if the area is seismically
active. Sudden changes in climate can
also play a role in causing a breach, such as during a year of anomalously wet
conditions (Bajracharya et al.,
2002).
A Technical Review of Glacial
Lakes and Glacial Lake
Outburst
Currently, much of the work that
is being input into this field is in the form of observation and monitoring,
that being hazard analysis as opposed to remediation of the problem at the
known dangerous lakes. Owing to the
remoteness of many of these lakes [11],
the primary tools now used in assessing hazards are remote sensing data and GIS
[12]
software. This has been made far more
achievable since the development of high resolution sensors such as those
onboard the earth observation satellite SPOT-5 [13]
(Huggel et al., 2004). These data can then be used to generate DEMs [14]
(see Figure 4) that recreate the terrain in three dimensions, such that models
of water and debris-flow can be run that assess the potential impacts
downstream (see Figure 5).
Figure 4:
Examples of DEMs produced for the Gruben area of the Swiss Alps.
The left image is generated from
aerial photogrammetry, the right image from satellite imagery (Source: Kääb et al., 2002)
Figure 5: Digital simulation of the August
1985 Dig Tsho outburst, produced from ASTER [15]
imagery. The modelled path of the flood has been depicted by a colour-transition
from red, through orange and yellow to green.
Red indicates that the model has predicted a high probability for
that area to be seriously affected by the flood, whilst green predicts a low probability. In
general, the model comprising ASTER imagery and DEMs has produced a very good
representation of the observed flood event, proving its potential in modelling
potentially hazardous lakes (Source: Kääb
et al., 2002).
In association with UNEP, ICIMOD
produced in 2001 detailed inventories of glacial lakes in
Another lake that has received a great deal of attention
is Tsho Rolpa in the Rolwaling valley (see Figures 6, 7 and 8). It is now six times larger than it was in the
1950s and research from groundwork and remote sensing has indicated that the
lake now represents a serious risk to people, livestock, property and
infrastructure [17]. Recently, engineers aided by Reynolds
Geo-Sciences Ltd., have been working to try to reduce the amount of water
contained in the lake, through the construction of a spillway, and therefore to
minimise the flood risk (Reynolds, 1999) (see Figure 9).
Figure 6:
Tsho Rolpa glacial lake, Rolwaling (Source: Google Earth) Figure 7: Rolwaling valley,
Figure 8: Looking downstream towards the
terminal moraine dam of Tsho Rolpa.
Note the lateral moraines on
either side of the lake (Source: Reynolds Geo-Sciences Ltd. (RGSL), 2005)
Figure 9: Tsho Rolpa GLOF Risk Reduction Project (Source: Reynolds Geo-Sciences Ltd. (RGSL), 2005)
Further Research Requirements
Much work is still required in order to help prevent
serious disasters occurring in the future.
The first step is to continue to monitor those lakes that are known to
be potentially dangerous. There is still
great concern for the safety of the people living downstream of Tsho Rolpa,
despite all the engineering work that has already been undertaken.
There is now a pressing urgency to accurately assess the
impending hazards at other sites. In
this regard, better use needs to be made of the detailed satellite imagery that
is now available in order to produce updated inventories [18].
With the development of even more powerful scanners, the
spatial resolution should become ever better into the future, and it is hoped
that these techniques will become more affordable in time, particularly as the
Nepalese government lacks the funds to implement even basic prevention
strategies (Kattelmann, 2003).
However, prevention costs are far lower than the prospect
of another large outburst. Therefore,
the use of modern remote sensing and cartographic techniques are essential to
monitor and analyse the current threat (Cunha, 1998). It is also vital that there is sound analysis
of the results of investigation, so that funds can be directed towards the most
pressing cases. In this respect,
transparency of information is also required so that both governments and
inhabitants are knowledgeable of the threats.
Conclusions
With the continued rising of global temperatures that are
expected during this century, this problem is likely to exacerbate even
further, the hazards for those living in mountainous regions are set to become
very severe. However, it is a problem
that is unusual in that it is possible to monitor the issue now, so that future
disasters can be avoided before they occur.
Funds will be needed from external sources, such as the other state
governments, but with input, the problem can be met with effective strategies
that ultimately save lives and livelihoods.
References
Bajracharya,
S. R., P. K. Mool and S. P. Joshi (2002), Spatial Database Development of Glaciers and Glacial Lakes in the
Identification of Potentially Dangerous Glacial Lakes of Nepal using Remote Sensing
and Geographic Information Systems, Asian
Association on Remote Sensing, 2002.
http://www.gisdevelopment.net/aars/acrs/2002/env/236.pdf
British Broadcasting Corporation (BBC), Himalayan
Warming May Trigger Floods, BBC News: Science and Technology.
http://news.bbc.co.uk/1/hi/sci/tech/1926667.stm
Cunha, S. F. (1998), Hazardous Terrain: The Need
for High Mountain Cartography and Remote Sensing in the Pamir Mountains,
Tajikistan, Proceedings
of the 5th International Symposium of the Use of Remote Sensing Data in
Mountain Cartography,
University of Graz, pp. 39-50.
http://www.uni-graz.at/geowww/hmrsc/pdfs/hmrsc5/Cunha_hm5.pdf
Dyurgerov, M. B. and M. F. Meier (1997), Mass
Balance of Mountain and Sub-polar Glaciers: A New Global Assessment for
1961-1990, Arctic and Alpine Research, 29 (4), pp. 379-391.
Huggel,
C., A. Kääb, W. Haeberli and B. Krummenacher (2003), Regional-scale GIS-models for Assessment of Hazards from Glacier Lake
Outbursts: Evaluation and Application in the Swiss Alps, Natural Hazards and Earth System Sciences,
3, pp. 647–662.
Huggel,
C., A. Kääb,
Kääb, A., C. Huggel, F. Paul, R. Wessels, B. Raup,
H. Kieffer and J. Kargel (2002), Glacier Monitoring from Aster
Imagery: Accuracy and Applications, EARSeL eProceedings, 2, pp. 43-53.
Kattelmann, R. (2003), Glacial
Ochoa, G., J. Hoffman and T. Tin
(2005), Climate, Rodale
International,
Raper,
S. C. B. and R. J. Braithwaite (2006), Low Sea Level Rise Projections from
Mountain Glaciers and Icecaps under Global Warming, Nature, 439,
pp. 311-313.
Reynolds,
J. M. (1999), Glacial Hazard Assessment
at Tsho Rolpa, Rolwaling, Central Nepal, Quarterly Journal of
Engineering Geology, 32, pp. 209–214.
Reynolds,
J. M. and P. J. Taylor (2004), Book Review: Mool, P. K., S.
R. Bajracharya, and S. P. Joshi (2001), Inventory of Glaciers, Glacial Lakes and Glacial Lake Outburst Floods,
Monitoring and Early Warning Systems in the Hindu Kush-Himalaya Region: Nepal,
and Mool, P. K., D. Wangda, S. R. Bajracharya, K. Kunzang, D. R. Gurung
and S. P. Joshi (2001), Inventory of
Glaciers, Glacial Lakes and Glacial Lake Outburst Floods, Monitoring and Early
Warning Systems in the Hindu Kush-Himalaya region: Bhutan, Mountain Research and Development, 24,
3, pp. 272-274.
Shrestha, M. L. and A. B. Shrestha
(2004), Recent Trends and Potential Climate Change Impacts on Glacier
Retreat/Glacier Lakes in
http://www.oecd.org/dataoecd/0/17/33993644.pdf
Shrestha,
A. B., C. P. Wake, P. A. Mayewski and J. E. Dibb (1999), Maximum Temperature Trends in the Himalaya
and Its Vicinity: An Analysis Based on Temperature Records from
SPOT-5: Observing Earth.
http://spot5.cnes.fr/gb/index3.htm
United Nations Environment
Programme (UNEP) and International Centre for Integrated Mountain Development
(ICIMOD) (2002), Glaciers, Glacial Lakes and Glacial
http://www.rrcap.unep.org/ew/glacial/allpostersfor2002april15&16.pdf
World Meteorological Organization (WMO), Edited by
Burroughs, W. (2003), Climate into the
21st Century,
World
Wildlife Fund (WWF) (2005), An Overview
of Glaciers, Glacier Retreat, and Subsequent Impacts in
http://assets.panda.org/downloads/himalayaglaciersreport2005.pdf
Further Reading
Bax, G. and M. F.
Buchroithner (Eds.) (1998), High-Mountain Remote Sensing Cartography
1998, Proceedings of the 5th
International Symposium of the Use of Remote Sensing Data in Mountain
Cartography,
University of Graz.
Cenderelli,
D. A. and E. E. Wohl (2001), Peak Discharge Estimates of Glacial-Lake Outburst
Floods and “normal” Climatic Floods in the Mount Everest Region, Nepal, Geomorphology, 40, pp. 57–90.
Duncan,
C. C., A. J. Klein, J. G. Masek and B. L. Isacks (1996), Comparison of Late
Pleistocene and Modern Glacier Extents in Central Nepal based on Digital
Elevation Data and Satellite Imagery, Quaternary
Research, 49, 241–254.
Germanwatch
(2004), Glacial
http://www.germanwatch.org/download/klak/fb-gl-e.pdf
Huggel,
C. (2004), Assessment of Glacial
Hazards based on Remote Sensing and GIS Modeling, University of Zurich.
http://www.dissertationen.unizh.ch/2004/huggel/diss.pdf
Huggel, C., A. Kääb, W. Haeberli, P. Teysseire and
F. Paul (2002) Remote Sensing Based Assessment of Hazards from
Raper,
S. C. B. and R. J. Braithwaite (2005), The Potential for Sea Level Rise: New
Estimates from Glacier and Ice Cap Area and Volume Distributions, Geophysical Research Letters, 32, L05502.
Reynolds
Geo-Sciences Ltd. (RGSL) (2003), Development
of Glacial Hazard and Risk Minimisation Protocols in Rural Environments:
Project Summary Sheet 6, RGSL.
http://www.geologyuk.com/mountain_hazards_group/pdf/proj_summ_06_R7816.pdf
Reynolds
Geo-Sciences Ltd. (RGSL) (2005), Tsho
Rolpa GLOF Risk Reduction Project: Project Summary Sheet 2, RGSL.
http://www.geologyuk.com/mountain_hazards_group/pdf/proj_summ_02_tshorolpa.pdf