The Andes

As glaciers in mountain areas recede in response to climatic warming, a number of different glacier hazards can develop. Richardson and Reynolds (2000) have identified two main types of glacial hazard (Table 1). Direct glacial hazards involve the direct action of snow and ice and include events such as snow and ice avalanches, glacier outburst floods and glacial advances. Indirect glacial hazards arise as a secondary consequence of a glacial feature or process

Table 1

Types of glacier, glacial and related hazards

Category

Hazard event

Description

Time scale of event

Direct

Avalanche

Slide or fall of large mass of snow, ice and rock

Minutes

Glacier outburst

Catastrophic discharge of water under

Hours

flood

pressure from a glacier

Jokulhlaup

Glacier outburst flood often associated

Hours to

with subglacial volcanic activity

days

Glacier surge

Rapid increase in rate of glacier flow

Months to years

Glacier

Variations in ice-front positions

Years to

fluctuations

decades

Indirect

Glacial lake

Catastrophic outburst, typically from a

Hours

outburst floods

moraine-dammed proglacial lake

(GLOFs)

Debacle

French term for an outburst from a proglacial lake

Hours

Aluvion

Spanish term for a catastrophic flood of liquid mud

Hours

Lahars

Catastrophic debris flow associated with rapid melt during volcanic activity

Hours

Water resource

Water supply shortages, particularly

Decades

problems

during low flow conditions, associated with wasting glaciers and climate change, etc.

and may include catastrophic breaching of moraine-dammed lakes or water resource problems associated with wasting glaciers and climate change. One of the principal glacier hazards is the threat posed by catastrophic drainage of hazardous moraine-dammed lakes, often known as glacial lake outburst floods (GLOFs). The number and volume of potentially hazardous moraine-dammed lakes is increasing in both the Himalaya and the Andes. These lakes develop behind unstable ice-cored moraines, and have the potential to burst catastro-phically, producing devastating floods. Discharge rates of 30 000 m3 s-1 and run-out distances in excess of 200 km have been recorded from Himalayan GLOFs. Glacial hazards have attracted attention recently for two main reasons:

(i) the risk of loss of life; and (ii) the serious threat to costly infrastructures such as hydropower installations, roads and communications. Carey (2005) has discussed the impacts of these glacier hazards on people living with these risks in Peru. The image below shows the aftermath of a glacial lake outburst flood (GLOF) in the Nepal Himalaya showing a large breach through a moraine and spread of gravel deposited during the GLOF.

Source: Carey, M. (2005) Living and dying with glaciers: people's historical vulnerability to avalanches and outburst floods in Peru. Global and Planetary Change, 47, 122-34. Table modified from: Richardson, S.D. and Reynolds, J.M. (2000) An overview of glacial hazards in the Himalayas. Quaternary International, 65/66, 31-47. [Photograph: N.F. Glasser]

transporting and depositing large quantities of sediment for tens of kilometres along their flood routes.

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