1) Satellite images detected the disappearance of a large supraglacial lake on Tshojo Glacier in Bhutan between March and July 2009, coinciding with a glacier outburst flood event.
2) The lake volume was estimated at 1.47 million cubic meters based on a post-flood DEM, suggesting it was an adequate source for the flood waters.
3) Subsequent images showed the lake beginning to refill in late 2010, indicating its behavior should continue to be monitored to predict future flood risks.
2. 28/July/2011, IGARSS11@Vancouver
What is GLOF?
GLOF (Glacier Lake Outburst Flood)
Sudden discharge of large volumes of water 1969
from the lake which lie at the end of glacier.
Mountainous glaciers has been retreating in
this 50years 2006
Might have relation with global warming
Expansion of glacial lakes
Landslide Avalanche RISK and TRIGGER of GLOF
Vulnerability 1) Lake with full of water
Of Moraine 2) Occurrence of glacier avalanche,
Dam outbreak of calving ice ,trigger to
Glacial Lake flooding
3) Increasing vulnerability of moraine dam
Glacier
due to melting of ice core, seepage etc.
Image form Iwata et. al, E-journal GEO vol.2 (1) 2007
3. 28/July/2011, IGARSS11@Vancouver
Introduction
• Sudden water outburst event
occurred in 29,Apr., 2009 at
Tshojo Glacier, Bhutan
• Tshojo Glacier is D-type glacier
and has no glacier lake : Strange
event…
• Approx. discharged volume is 0.5
million m3 (Komori, 2011)
• However, its water source was
not found from ground survey
• Ground survey is quite difficult
due to severe geographical
condition Tshojo Glacier
28, Oct., 1986
SPOT-2 / XS
4. 28/July/2011, IGARSS11@Vancouver
Field Survey shows…
- Debris flow started from lower part of Tshojo Glacier terminus
- Debris flow blew out from under the surface of glacier
Tshojo Glacier 2009 GLOF
Lower end of
glacier was
eroded
5. 28/July/2011, IGARSS11@Vancouver
ALOS PRISM, Jan.
Field Survey photos
2010
we tried to search the source of the water.
Estimated discharge volume is bigger than hollow and pond.
80 x 90m, dep.20 m
Surrounded by ice
cliff
Dried up ice tunnel is
exposed 1.4 km from outlet.
Flooded water come down via these 100x100m dep. 20m
channel
ALOS/PALSAR image told us
the source of outflow water!
6. 28/July/2011, IGARSS11@Vancouver
View from the space !
• Two ALOS/PALSAR image detected a sudden disappearance event of a
large supra-glacial lake on Tshojo Glacier
• The lake seems to be adequate source of the flood. It is necessary to
estimate the volume of this lake and to check the validity of our hypothesis
7, March, 2009 23, July, 2009
7. 28/July/2011, IGARSS11@Vancouver
Objectives
• To investigate the relationship between flood
event and disappearance of supraglacial lake
through the analysis of time series satellite data
• To estimate the lost water volume of supraglacial
lake by ALOS/PRISM DSM
• To validate quantitatively the relationship between
water volume of supraglacial lake and increased
river water volume estimated from water gauge
• To investigate the similar event trough satellite
data analysis
9. 28/July/2011, IGARSS11@Vancouver
Preprocessing
• ALOS/PALSAR:
Apply orthorectification and radiometric terrain correction
• ALOS/AVNIR-2:
Use orthorectified data. If PRISM has simultaneous
observation, applied pansharpening
• ALOS/PRISM:
Use orthorectified image for pansharpening and DSM
extraction from triplet image
• SPOT/HRV:
Apply orthorectification using SRTM-3 DEM. If PA has
simultaneous observation, applied pansharpening
10. 28/July/2011, IGARSS11@Vancouver
Results: Time series satellite images
•Lake started to form from Oct., 2008(Yellow circle)
•No relation with cyclone Aila
•Lake started to re-fill from Dec., 2010
•Due to freezing water, SAR is difficult to interpret
•Stable supraglacial lakes exist near here(Red circle)
20070302 20070902 20071226
Cyclone Aila
Flood event
20080108 20080419 20081020 20090120 20090307 20090424 20090519 20090723
20090907 20091125 20091208 20100117 20100123 20100310 20101205 20110126
11. 28/July/2011, IGARSS11@Vancouver
Results : expanded image around the lake
ALOS / PALSAR SPOT / HRV •Shapes of lake coincided
between SAR and opt.
•Re-filling clearly detected
•Long radius:500m (yellow)
•Short radius:300m (light blue)
•Area size : 117532m2
•Flow velocity is quite slow
20090307 20090424
SPOT / HRV ALOS / PALSAR ALOS / AVNIR-2
20090519 20090723 20101205
Start re-filling
12. 28/July/2011, IGARSS11@Vancouver
Results estimation of water volume from PRISM DSM
Deepest point ：4174m (Yellow star )
Lake surface ：4224m (Red line)
Estimated water volume from ALOS / PRISM DSM :
1464700 m3
Approx 3 times larger than estimation by Komori (500000m3)
13. 28/July/2011, IGARSS11@Vancouver
Summary and Future plan
Time series satellite data analysis revealed the disappearance of
supraglacial lake occurred after flood event and no relationship with
flood by cyclone Aila. It implies the relationship between flood event
and disappearance of supraglacial lake
Satellite image clearly detected the re-filling of lake water from Dec.,
2010 ALOS / AVNIR-2 image. It is necessary to pay attention to flood
event again
Ellipsoidal height of deepest point and surface of supraglacial lake is
estimated to 4174m and 4224m respectively. Its volume is 1464700 m3
More quantitative research will be necessary through the combined use
of river gauge data and river flow simulation data with satellite data
Supraglacial lake on Juchudake glacier shows similar seasonal change.
We will continue to research the behavior of this lake using ground truth
survey data (This May research survey was held)
14. 28/July/2011, IGARSS11@Vancouver
Acknowledgements
• This research was supported by JST-JICA,
SATREPS project.
• ALOS / PALSAR data were provided by JAXA
through the ALOS PI project (PI No. 577)
Thank you very much for your attention!
15. 28/July/2011, IGARSS11@Vancouver
Acknowledgements
• This research was supported by JST-JICA,
SATREPS project.
• ALOS / PALSAR data were provided by JAXA
through the ALOS PI project (PI No. 577)
125000
120000
Variation of area size of lake 115000
•SAR image acquired on Jan., 2009 110000
105000
showed less size due to the frozen 100000
lake surface water 95000
•AVNIR-2 image acquired on Dec. 90000
2010 showed the re-filling of 85000
supraglacial lake 80000
2009/04
2010/12
2008/10
2009/01
2009/03
0.5
