Melting of glaciers is one of the major effects of recent atmospheric warming in the Himalayas which results in the development of supraglacial lakes that coalesce to form proglacial lakes. Large volumes of water in these lakes are considered dangerous due to its unstable surrounding geomorphology. Most of the proglacial lakes are moraine-dammed and breaching of such moraine due to some triggering events may give rise to rapid release of water and sediment, often termed as Glacial Lake Outburst Floods (GLOFs). GLOFs represent catastrophic phenomenon of the Himalaya and pose a risk to downstream communities and infrastructure. Several GLOF events have been recorded in Nepal in the past few years. Since 1990s, the lake area of Thulagi has increased from 0.72 to 0.94 km 2 while that of Lower Barun has increased from 0.64 to 2 km 2 and both glacial lakes rank No. I in the Potentially Dangerous Glacial Lakes (PDGLs) in Nepal. In this study, NWS-BREACH and HEC-RAS model are used to access the impact of GLOF on downstream areas. Different dam breach scenarios of 5, 10, 15 and 20 m is evaluated by NWS-BREACH model to estimate the breach hydrograph. The peak flow at the time of breach ranges from 1400 to 5400 m 3 /s for Thulagi and 2600 to 7900 m 3 /s for Lower Barun in low and high breach scenarios respectively. The peak flow estimated from NWS-BREACH is used for the flood routing in HEC-RAS to simulate peak discharge and flood height at different distances in the downstream from the lake outlet. The impact on downstream regions of the two glacial lakes is then evaluated by flood inundation map to access the land exposed to GLOF. Nepal consists of large number of glacial lakes and only a few have been studied. Furthermore, detail field survey of the lakes and downstream areas need to be incorporated for better prediction of GLOF events.

Himalayan glaciers, in general, are shrinking and glacial lakes are evolving and growing rapidly in number and size as a result of climate change. This study presents the latest remote sensing-based inventory (2017) of glacial lakes (size ≥0.0036 km2) across the Nepal Himalaya using optical satellite data. Furthermore, this study traces the decadal glacial lake dynamics from 1977 to 2017 in the Nepal Himalaya. The decadal mapping of glacial lakes (both glacial-fed and nonglacial-fed) across the Nepal Himalaya reveals an increase in the number and area of lakes from 1977 to 2017, with 606 (55.53 ± 16.52 km2), 1137 (64.56 ± 11.64 km2), 1228 (68.87 ± 12.18 km2), 1489 (74.2 ± 14.22 km2), and 1541 (80.95 ± 15.25 km2) glacial lakes being mapped in 1977, 1987, 1997, 2007, and 2017, respectively. Glacial lakes show heterogeneous rates of expansion in different river basins and elevation zones of Nepal, with apparent decadal emergences and disappearances. Overall, the glacial lakes exhibited...

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Glacier lake outbursts in Switzerland - mechanisms and measures untertaken to prevent further outbursts (Sirvoltesee, Weingartensee, Grubensee) Neben Längen- und Geometrieveränderungen, Gletscher- und Eisstürzen stellen Gletscherhochwasser eine der wichtigsten von Gletschern ausgehende Gefahr dar. Gletscherhochwasser entstehen bei dem plötzlichen Auslaufen von auf, in, neben oder unter Gletschern gelegenen Schmelzwasserreservoirs. Die durch das mög- liche Auslaufen der Schmelzwasserreservoirs bewirkten Flutwellen können grosse Geschiebemengen mobilisieren und Murgänge auslösen, welche an flussabwärts gelegenen Siedlungen und Infrastrukturanlagen beträchtlichen Schäden anrichten. Das Phänomen der Gletscherseen ist aus allen vergletscherten Gebirgsregionen be- kannt. Im vorliegenden Beitrag werden der Sirvoltesee, der Weingartensee und die Gru- benseen vorgestellt. Für diese in den südlichen Walliser Alpen gelegenen Gletscher- seen werden Ausbruchmechanismen aufgezeigt und die zum Schutz vor zukünftigen Ausbrüchen unternommenen Massnahmen vorgestellt. Die Erfahrung mit diesen Seen zeigt, dass das von Gletscherseen ausgehende Risiko mit Hilfe eines Schutz- konzeptes teilweise beherrschbar gemacht werden kann. Ein Schutzkonzept sollte neben allfälligen baulichen Massnahmen ein Interventions-, Beobachtungs- und In- formationskonzept umfassen. Es muss den spezifischen Gegebenheiten eines Glet- schersees Rechnung tragen. Damit Sanierungsmassnahmen rechtzeitig realisiert werden können bedarf es eines frühzeitigen Erkennens allfälliger Gefahrenherde. Bisher gibt es jedoch noch kein funktionierendes Früherkennungskonzept für solche Gefahren.