Why risk-monitoring in the Himalayas is like looking for 'needles in haystacks', Pg17

Key Highlights:

• Recent floods in Nepal were triggered by a glacial detachment, possibly involving bedrock, on the northern slopes of Langtang Lirung peak in the Langtang range.
• The event created a temporary natural dam on the Lhende River, which subsequently failed, sending a massive flood pulse downstream.
• The flood, described as a "thousand-year-plus event," caused significant destruction over 100 kilometers, affecting hydropower projects and villages in Nuwakot district.
• The incident highlights the increasing frequency and intensity of cascading hazard chains in the Himalayas, similar to events like the South Lhonak GLOF in Sikkim.
• Monitoring every potential hazard site in the Himalayas is challenging, requiring a multi-pronged approach combining remote sensing, fixed stations, and local community involvement.

Detailed Insights:

• The exact triggering process of the glacial detachment is not fully understood but may be linked to climate-related risks or gradual shifts.
• The flood pulse reached the China border in approximately nine minutes, sweeping away individuals who could have issued alerts.
• The event destroyed dams and hydropower projects and affected market towns in the floodplains, extending beyond typical flood zones.
• Previous similar events in the region include the Chamoli disaster and the Melamchi disaster in Nepal.
• Most extreme events in the Himalayas over the last decade originated from previously unidentified locations, except for the South Lhonak GLOF.
• India's Home Ministry and space agencies undertake mapping exercises for glacial lakes and hazards, a level of resource Nepal currently lacks.
• A comprehensive monitoring strategy requires remote sensing, fixed station networks (hydromet and seismic), and localized community monitoring.
• Engaging local communities, including yak herders and fishermen, and utilizing oral histories can help identify potential hotspots and changes.

Key Concepts Involved:

• Glacial Detachment: The separation of a mass of ice and rock from a glacier, often leading to landslides or floods.
• Cascading Hazards: A series of interconnected natural hazards where one event triggers subsequent, often more severe, events.
• Glacial Lake Outburst Flood (GLOF): A sudden release of water from a glacial lake, often caused by the failure of a natural dam.
• Remote Sensing: The acquisition of information about an object or phenomenon without making physical contact, typically using satellites or aircraft.