Did a large chunk of detached moraine cause South Lhonak Lake burst causing the devastating deluge?

The studies revealed that the detached moraine fell and pushed into the deepest portion of the lake, resulting in an overflow of a large volume of water from the outlet

The swelling of the Teesta river basin that ravaged North Sikkim killing close to 50 people and 150 still missing, was caused by the detachment of the moraine (rocks and debris) which fell into the South Lhonak Lake, resulting in the overflow of a large volume of water that led to the widening and deepening at the outlet of the lake, satellite images revealed.

The South Lhonak Lake is located at an altitude of 17,100 feet in the upper reaches of northern Sikkim, not too far from the India-China boundary.

The Department of Science and Technology, Sikkim, did a comparative study of the satellite images of the lake taken on September 26 and October 6 and inferred that there has been a detachment of the side wall (northwest side) of the lateral moraine (rocks and debris) of the South Lhonak Lake, measuring approximately 600m length x 225m height x 150m width from the surface level of the lake.

As per the data available, the moraine eventually plunged into the lake.

What is a Moraine?

Moraine which is an accumulation of unconsolidated debris (rock and soil), is left behind by a moving glacier.

As the river carry along all sorts of debris and silt that eventually builds up to form deltas, glaciers transport all sorts of dirt and boulders that build up to form moraines.

Moraines are formed in places that have or used to have, glaciers.

The studies revealed that the detached moraine fell and pushed into the deepest portion of the lake, resulting in an overflow of a large volume of water from the outlet, which has led to widening and deepening at the outlet of the lake, a release from the Science and Technology Department stated.

Further, the studies show that due to the overflow of water from the lake, there has been a decrease in water level from 162 ha to 144 ha.

However, during this entire sequence of events, it has been observed that, as per the available data, the main moraine damming the lake remains in its original position and shape.

The recent disaster as a result of overflow of South Lhonak Lake is being closely monitored with the help of different satellite data.

Besides those dead and missing, around 25,000 people have been affected and 1,173 buildings have been damaged. Almost 900 vehicles have been washed away. As per inputs 2,143 persons have been rescued so far.

Copy edited by – Haynashree Narjary

Also Read: What is GLOF? Which caused catastrophic floods in Sikkim killing 30 people so far. Read to know more

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