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Glacier lakes are common phenomena in the Himalaya region of Nepal. Glacier lake outburst floods have repeatedly caused the death tolls and severe damage to downstream infrastructures. In Himalayas, a vital uncertainty about the glacier lake hazard potential still exists, thereby the effects of accelerating rates of glacier retreat and expansion of Glacier Lake could be the wake of recent global warming and resulting climatic changes. The paper, first describes the general different-level approach upon which the study is based. Then, in the methodological part, applicable remote sensing techniques, geographic information system (GIS) and statistical methods are presented. Observed data of lake area, volume, and depth having similar lake characteristics reported in the different literature are used to develop empirical equations by using statistical methods. The values of r 2 (coefficient of determination) - obtained are very high (r 2 =0.939 for depth – area relationship and r 2 = 0.990 for volume – area relationship). The comparison of the empirical expression clearly indicated that there is more than 90% variation in the dependent variable, lake volume,as explained by the linear regressions in both cases. Area of Imja glacier lake for different years are determined from the available satellite imagery and volume of the Imja glacier lake are estimated using the expression: V = 0.094 A 1.453 .developed from linear regression analysis of the observed data. Similarly, mean depth can be estimated by using the expression: D = 0.94 A 0.452 . After the preparation of maps and data, a scheme of decision criteria for the evaluation of hazard potential of Imja glacier lake is established. A list of decision criteria is a documented set of factors that are used to examine and compare for evaluating the hazard potential of a glacier lake. The empirical scores are given in terms of hazard magnitude for hazard rating. Analysis of Imja glacier lake based on the empirical scoring system clearly indicated that GLOF risk of the possible outburst from Imja glacier lake is MODERATE . A systematic application of remote sensing based methods for glacier lake outburst flood risk assessment is applicable and thus recommended. Keywords: Glacier lake outburst; remote sensing; risk assessment; hazard potential; empirical parameters; climate change DOI: http://dx.doi.org/10.3126/jhm.v7i1.5618 JHM 2010; 7(1): 75-91

INTRODUCTION Glaciers in Alaska cover an area of about 73,800 square kilometers (28,500 square miles). They are most highly concentrated along the Pacific Coast and in the south-central part of the State. Many of these glaciers, as elsewhere in the world, flow across the mouths of adjoining valleys and cause lakes to form behind the ice streams. These glacier ice dams are subject to repeated failure. Because most Alaskan communities and transportation routes are situated along rivers which flow from glaciers the hazards presented by glacier dammed lakes are serious. The damage by floods from these lakes will increase if people encroach into areas where flooding occurs. Glacier dammed lakes in south-central and southeastern Alaska and in adjacent Canada which drain into rivers entering Alaska are included in this study. Such lakes are numerous in this area; 750 glacier dammed lakes have been plotted on the maps on sheets 1 and 2. The number and size of individual lakes vary enormously during the seasons and from year to year; the total number of lakes plotted provides an indication of their abundance. Not included in this report are the few, very small lakes dammed by glaciers that are widely scattered in the Brooks Range, Alaska Peninsula, Kodiak Island, and Aleutian Islands. The major hazard presented by glacier dammed lakes is catastrophic flooding which occurs when the ice dams fail. In many places flooding occurs annually; there are many exceptions and the situations change rapidly from one year to the next. It should be noted that large quantities of water can also be stored in or under glaciers and may create serious floods even though no surface lake is visible. Such catastrophic floods have occurred in Iceland so frequently (Thorarinsson, 1953) that the Icelandic term "jokulhlaup" is now used internationally to describe them. In the State of Washington floods of this nature have been observed from at least four glaciers (Richardson, 1968). Thus, glaciers with no visible lakes may present unusual flood hazards. However, one cannot identify from aerial photographs or maps those glaciers which are likely to produce large jokulhlaups except to note a common association of glacier outburst floods with glacier-clad volcanoes. Any glacier may produce an outburst flood, but only visible glacier dammed lakes and glaciers on volcanoes are shown in this report. The largest glacier outburst floods in Alaska are from the release of glacier dammed lakes. The purpose of this report is to present an up-to-date assessment of the hazardous glacier outburst floods in Alaska by mapping the present extent of glaciers, the location of glacier dammed lakes and glacier-clad volcanoes, presenting the recent history of several prominent glacier dammed lakes, and delineating areas where outburst flooding may be expected. Avoiding particularly hazardous situations is advised and recommendations are made for monitoring a few lakes which cause very large or potentially damaging floods.