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Glaciers
 
A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. A glacier is formed by ice accretion over years on a sloping terrain. Glacier ice is the largest reservoir of freshwater on Earth, and second only to oceans as the largest reservoir of total water. Glaciers can be found on every continent except Australia.
There are two main types of glaciers:
    - Alpine glaciers, which are found in mountain terrains
    - Continental glaciers, which are associated with ice ages. Today, Greenland and Antarctica are such areas.
The smallest alpine glaciers that form in mountain valleys are referred to as valley glaciers. Larger ice layers can cover an entire mountain, mountain chain or even a volcano; this type is known as an ice cap. Ice caps feed outlet glaciers, tongues of ice that extend into valleys below, far from the margins of those larger ice masses. Outlet glaciers are formed by the movement of ice from a polar ice cap, or an ice cap from mountainous regions, to the sea.  
 
Profile of typical alpine glacier
 
CIRQUES: semi-circular shaped bedrock feature created as a glacier scours back towards the mountain (highest place where snow and ice accumulate).
ARÊTE OR CREST: steep-sided, sharp-edged bedrock ridge formed by two glaciers eroding away on opposite sides of a ridge.
HORNS: 3 or more cirques adjacent to one another.
TARNS: glacial lakes produced by glacial scouring - often found in cirques.

 
 
Some terms referring to glaciers
 
 
Glaciers form landscapes
 
A glacial lake is a lake with its origins in a melted glacier.
At the end of the last ice age, retreating glaciers often left large sections of ice behind. As this ice melted, lakes were created. Today these lakes are often found surrounded by rolling hills, also called drumlins, along with other evidence of the glacier, such as moraines, eskers and erosional features such as striations and chatter marks on big rocks which were transported by the glacier. Such rocks are called erratic rocks. All these features can also be found in the foreland of the Alps.
 
 
Glacial lake outburst floods
 
Today, as the glaciers retreat in high mountainous areas, they leave a large void behind. Ponds occupy the depression earlier occupied by glacier ice. The shores are made of moraines, which are dams of structurally weak and unstable sand, pebbles and rocks, and undergo constant changes due to slope failures, slumping, etc. They run the risk of breaking due to the pressure of the rising lake levels.
Principally, a moraine dam may break as a consequence of some external trigger or self-destruction.

Such glacial lake outburst floods (GLOFs) are catastrophic discharges of water resulting primarily from melting glaciers. An accelerated retreat of the glaciers in recent times has led to an enlargement of many glacial lakes. A huge displacement wave, generated by rockslide or a snow/ice avalanche from the glacier, may cause a GLOF.
The mapping and monitoring of such glacial lakes is, in spite of their danger, very costly mainly because of their remoteness. Images taken from satellites are therefore an important tool for surveillance.
 
 

 


Monitoring of glaciers in the Himalayas
IntroductionInvestigation areaKhumbu's glaciersImja glacier
Exercises
Location of the study area, Khumbu HimalDevelopment of glacial lakes in the Khumbu HimalGlacier retreat at Honku glacier
Links
Further Reading
Eduspace - Software
LEOWorks 3
Eduspace - Download
glacier_worksheet1.zipglacier_worksheet2.zipglacier_worksheet3.zip
 
 
 
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