What caused the sudden deadly flooding in Nepal?
By el Amigo
MANILA — The catastrophic flooding that struck Nepal’s Rasuwa district near the China border was not simply the result of heavy rain.
The disaster appears to have been triggered by a massive glacier collapse and avalanche of ice and rocks high in the Himalayas.
According to experts, a large mass of ice and debris plunged into a mountain valley, blocking the Lhende Khola River, a tributary of the Bhote Koshi River. The blockage effectively created a temporary natural dam.
Then it failed.
The sudden release sent a powerful wall of water, mud, rocks and ice racing downstream, producing a flash flood with little warning for communities along the river.
HOW IT HAPPENED
GLACIER COLLAPSE
A large section of unstable ice and rock broke away from the mountain.
DEBRIS CRASHED INTO THE RIVER
The falling material blocked the Lhende Khola River.
TEMPORARY DAM FORMED
Water accumulated behind the debris, creating a dangerous buildup.
DAM GAVE WAY
The blockage suddenly collapsed, releasing the trapped water.
FLASH FLOOD SURGED DOWNSTREAM
A massive torrent carrying water, mud, ice and boulders swept through communities and infrastructure along the river.
WHY WAS IT SO SUDDEN?
The danger came from the speed of the release.
Unlike a slowly rising river caused by prolonged rainfall, a glacier-related outburst can release a tremendous volume of water almost instantly. The resulting debris flow can also become even more destructive as it picks up rocks, soil, trees and other material while moving downhill.
WAS IT AN EARTHQUAKE?
Apparently not.
A seismic signal initially raised the possibility of an earthquake. But subsequent analysis indicated that the signal was generated by the glacier collapse and resulting debris movement, rather than by a conventional earthquake.
WHAT ABOUT CLIMATE CHANGE?
Climate change is an important part of the bigger Himalayan picture.
Rising temperatures are causing glaciers to retreat and can contribute to changes in mountain ice, frozen ground and slopes. These changes may increase the instability of some high-altitude environments.
However, scientists still need more evidence before saying that climate change directly caused this particular glacier collapse.
THE BOTTOM LINE
This was a cascading mountain disaster: a glacier collapse triggered a debris blockage, the blockage failed, and the sudden release unleashed a destructive flash flood downstream.
IN THE KNOW:
What looked like a sudden flood was actually the final stage of a chain reaction that began high in the Himalayas—far above the communities that were eventually hit.
ia/xf
