Glacial Lake

Amid the tranquil landscapes of North Sikkim, a cataclysmic event recently unfolded—the outburst of the South Lhonak glacial lake. This unleashed a torrential flood, wreaking havoc downstream as it swept away major highways and settlements in its path.

Contents

Unveiling the Characteristics

A Glacial-Moraine-Dammed Lake

The South Lhonak lake is classified as a glacial-moraine-dammed lake, nestled at a breathtaking altitude of 17,000 feet in North Sikkim. What sets this lake apart is its astonishing expansion rate, making it the fastest-expanding glacial lake in the Sikkim Himalayas.

Rapid Expansion Evidenced

According to the Sikkim Forest and Environment Department, recent decades have witnessed a dramatic increase in the lake’s size. South Lhonak has grown nearly 2.5 times since 1989, while Lhonak itself has expanded by nearly 1.5 times during the same period.

Unraveling the Enigma

A Water Body Born of Glacial Activity

South Lhonak is a water body born from the remnants of glacial activity, making it a fascinating subject of study.

Geological Information Treasure Trove

The lake bed is rich in sediments—carried by glaciers over time—that hold invaluable geological information. These sediments, if preserved, can provide insights into fossils, landmass formation, and the earth’s history.

Varves and Rock Formations

Varves, which are annually laminated sediments, resemble tree rings and offer insights into the lake’s age, past climate, and glacier dynamics. Additionally, rock formations within the lake, including striations and physical weathering patterns, provide essential paleoclimatic information.

The Birth of Glacial Lakes

Glaciers: Nature’s Sculptors

Glacial lakes like South Lhonak form due to the retreat of glaciers. Glaciers, composed of compressed layers of snow, form at high altitudes and slowly move down mountain slopes when they become sufficiently heavy.

The Moraine Factor

As glaciers move, they scrape the mountain surface, creating wrinkles in the surrounding land and displacing debris. This debris, called moraine, acts as a natural barrier, preventing meltwater from the glacier’s tail from flowing freely and leading to the formation of moraine-bound glacial lakes, such as South Lhonak.

Another Lake Variety

In contrast, some glacial lakes are bound by ice. These form when a moving glacier settles in a deepened land, effectively blocking meltwater from a stationary glacier through higher landmass and the glacier’s own ice.

Factors Influencing Stability

The Role of Meteorological Conditions

The stability of glacial lakes is contingent on meteorological conditions in the region, particularly in the context of temperature and precipitation patterns.

Physical Triggers: Earthquakes and Loose Debris

For moraine-dammed glacial lakes, the presence of loose debris within the moraine is a critical factor. When this debris shifts, it can cause leakages or outbursts, leading to massive flooding downstream.

Intervention: Taming South Lhonak

In 2016, recognizing the looming threat, various agencies, including the Sikkim State Disaster Management Authority and Sikkim’s Department of Science, Technology, and Climate Change, embarked on an ambitious mission. They decided to syphon off water from the South Lhonak Lake, enlisting the expertise of innovator Sonam Wangchuk.

The Syphoning Technique

This daring endeavor involved the installation of three eight-inch wide HDPE pipes, each measuring 130-140 meters in length, within the lake. These pipes facilitated the controlled syphoning off of water from South Lhonak at a rate of 150 liters per second, as reported by the Sikkim State Disaster Management Authority.