Glacier Hazards From Space

Retreating valley glaciers often leave behind glacier lakes in front of or within their melting tongues. Nearly all glaciers in this image of the Bhutan Himalayas show lakes at their tongues. Once such a lake has formed, melting and retreat of the glacier front accelerates because water transports heat much more efficiently to the ice front than air can. The Bhutan Himalayas currently host more than 2,500 glacier lakes. On October 7, 1994, the greenish lake to the right in this image, Lugge Tsho, partially burst out. Though the impact in this lightly populated area was minimal—12 houses were damaged, five water mills washed away, and about 800 acres of land damaged—traces of the subsequent debris flow down the valley remain visible seven years later in this 2001 image. The glacier tongue seen in the middle of the image, between the blue and green lakes, shows clearly how small ponds forming on a melting glacier tongue can rapidly grow and connect with one another to form large, potentially hazardous lakes.