The diagram in Fig. 1 shows a recent mountain fieldwork investigation in Nepal. Villagers have built homes and vegetable terraces below a retreating glacier...
Question 1 Report
The diagram in Fig. 1 shows a recent mountain fieldwork investigation in Nepal. Villagers have built homes and vegetable terraces below a retreating glacier. Meltwater is held behind a loose moraine ridge, forming a growing glacial lake. The enquiry team heard cracking sounds from the slope and found that a narrow outlet stream passes through the village. Climate change is one possible cause of change in this high-altitude fragile environment. Use Fig. 1 and your knowledge of hazards linked to global warming.
(a) Identify the landform that is holding back the lake water in Fig. 1. [3]
(b) Describe the location of the village in relation to the glacial lake. [5]
(c) State three warning signs that could be used to alert people to a possible outburst flood. [7]
(d) Explain how warming can increase the risk of a glacial lake outburst flood and why this may affect development. [10]
Answer Details
(a) The lake is held back by a moraine ridge: a ridge of glacial debris that acts as a dam. [3]
(b) The village is downhill and downstream of the glacial lake, below the moraine ridge, on the valley floor or lower slope and beside the outlet stream. If the dam fails, floodwater could follow this stream directly towards the village. [5]
(c) Warning signs include a rapid lake-level rise, new cracks or slumping in the moraine, louder cracking or icefall sounds, increased meltwater flow, unusually muddy water, an automatic water-level alarm, heavy-rain forecasts, or reports of an avalanche or collapse entering the lake. Any seven valid signs gain credit. [7]
(d) Higher temperatures increase glacier melting, enlarging the lake and increasing water pressure on the moraine. Melting ice within the moraine can weaken it, while heavy rain can add water rapidly. An avalanche or rockfall entering the lake may displace water over the dam. Dam failure releases a sudden outburst flood, which can destroy homes, fields and bridges and cut roads, power and water supplies. Money and land intended for development must then be used for recovery or protection. [10]
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