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Lhonak Glacier (Sikkim Region, India)

Bangalore, February 2013 (From: Zee News) - A satellite-based study has indicated that a huge glacial lake has formed atop the Himalayas in Sikkim with a "very high" potential for it to burst and create devastation downstream. Analysis of satellite data has revealed that the lake has formed at the snout of South Lhonak glacier that is about 7,000 meters high on the mountain in the north-eastern state. The lake, bounded only by loose soil and debris, could cause havoc downstream if it ruptures, according to scientists at the National Remote Sensing Centre (NRSC) in Hyderabad. In a report published in the latest issue of the journal Current Science, NRSC researchers Babu Govindha Raj and co-workers say the glacial lake is about 630 meters wide and 20 meters deep. It covers an area of 98.7 hectares and contains 19.7 billion litres of water. A sudden outburst "can create devastating floods downstream," they warn, adding that the probability of this happening "is very high". They however note this is only their preliminary assessment and more field studies are required to confirm the hazardous potential of this high altitude lake. Data from the American Landsat satellite were used to estimate the size of the shrinking Lhonak glacier and the growth of the glacial lake at different times between 1962 and 2008. Based on this study the scientists estimate that the Lhonak glacier had receded 1.9 km between 1962 and 2008. The glacial lake that was initially a small body of water in 1962 grew in size with accumulation of melt water. The NRSC scientists say that the lake is still attached to the snout of the glacier but is expanding in area due to the glacier retreat. "The rate of growth of the lake indicates possible developments of the hazard situation," the report says. As Himalayan glaciers are retreating fast, it is necessary to make an inventory of glacial lakes and set up an early warning system for lake outburst floods in vulnerable areas, they say.

Area of interest
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ALOS AVNIR-2 images

These images acquired by ALOS' AVINR-2 sensor, show the same area of interest with a different spatial resolution and different band combination.

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Technical Information
Satellite: ALOS
Instrument: AVNIR-2 - Full Resolution (10 m)
Product: ALOS.AVNIR.2
Date of acquisition 19 Jan 2009
Coverage: 70 km (at Nadir)
Band combination: 3, 2, 1 and 4, 3, 2
ASAR_IMP Swath2 animation

These images taken by the Envisat and ERS satellites show details of the area using different images acquired during their missions. The animation shows the state of the glacier from October 2000 to August 2010.

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Technical Information
Satellite: ERS-1 and 2 and Envisat
Instrument: Advanced Synthetic Aperture Radar (ASAR) - Full resolution (10 m)
Product: ASA_IMP (level 1b)
Images used to create the animation
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ASAR_IMP multi-layer image of the area

This multi-colour image was created by merging Envisat and ERS-1/2 satellite images. The areas highlighted in green were acquired by ERS-2, and blue ERS-1, and show the changes to the glacier between these acquisitions.

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Technical Information
Satellite: ERS-1 and 2 and Envisat
Instrument: Synthetic Aperture Radar (SAR) / (ASAR) - Full resolution (30 m)
Product: ASA_IMP (level 1b)
Date of acquisition: 25 Aug 2010, 18 Aug 1999, 04 Oct 1992
Coverage: 100 km along track
Band combination: Multi-layer merge Envisat and ERS-1/2 (RGB)
Images used to create the multi-colour merge
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Landsat-5 and 7 animation from December 2000 to February 2010
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Images used to create the Landsat animation

These Landsat-5 and 7 satellite images show the lake recently formed at the snout of South Lhonak glacier during the last few years.

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Technical Information
Satellite: Landsat-5 and 7
Instrument: Thematic Mapper (TM) - Full Resolution (30 m)
Product: TM / ETM
Date of acquisition: Dec 2000 to Feb 2010
Coverage: 185 km x 185 km
Band combination: 7, 4, 2 (RGB)
Images taken from Google

This next set of three images taken from Landsat and Google Earth from 2000 (first image) 2006 (second image) and 2010 (third image), show the changes to the glacier during the years. The 2010 terminus is marked by green lines, 2006 the orange lines, and 2000 the magenta line. The glacier retreated 350 metres from 2000 to 2006 and 250 meters from 2006 to 2010.

View large image [JPG 330 KB]
Technical Information
Satellite: Landsat-5 and 7
Instrument: Thematic Mapper (TM) - Full Resolution (30 m)
Product: TM / ETM
Date of acquisition: 2000, 2006, 2010
Coverage: 185 km x 185 km
Map of area

The South Lhonak Glacier drains east from Lhonak Peak into Sikkim from the Nepal-Sikkim border. The glacier begins at the border at 6500 metres and ends in a lake at 5200 metres.

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