Introduction

Supraglacial lakes (or ponds) on the order of 100m or less in horizontal scale were located on the termini of Himalayan glaciers in the 1950s and 1960s. However, thereafter, they have been expanding by the glacial retreat after the Little Ice Age of the sixteenth to nineteenth centuries, and, at present, up to moraine-dammed lakes of 1 km scale [1]. The expansion of moraine-dammed lakes consists of horizontal expansion by calving at the glacial terminus and vertical deepening by ice-melting below the lake bottom [2]. Of all the moraine-dammed lakes, Tsho Rolpa, Rolwaling in the Nepal Himalayas, has the highest potential for GLOF (Glacial Lake Outburst Flood) [3, 4], which is produced by the collapse of the end moraine damming up the lakes. In order to prevent a GLOF at Tsho Rolpa, siphonal pumping in the monsoon season or gate construction on the end moraine by the cut-and-cover method [5] (URL: www.geologyuk.com/) was undertaken from 1995 to 2000. The contribution of the worldwide retreat of mountainous glaciers to an increase in the sea level has tended to increase in recent years [6, 7]. It should be noted that the glacial retreat in the Himalayas could not only increase the glacier-melt water input through the Ganges and Indus rivers to the Indian Ocean, but also produce serious disasters such as GLOFs.

In this chapter, the hydrodynamics of three moraine-dammed glacial lakes, Tsho Rolpa, Imja and Lugge, are compared from field observations, and the associated heat transport in the lakes is discussed by three-dimensional numerical simulations of wind and lake currents.

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