Lecture 19_Glaciers

# 3 m glacial ice cross sectional view fig a below zone

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3 M. Glacial ice Cross-sectional view (fig. A below) Zone of fracture (upper part of a glacier) Zone of plastic (=internal) flow Zone of basal slip /sliding (bottom part of a glacier, zone of ice is in contact with the ground) N. A B Zone of fracture Occurs in the uppermost 50 meters, When glacier moves over irregular terrain the zone of fracture is subjected to tension snow ice firn

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4 Tension causes crevasses to form in brittle ice Crevasses o Two types Transverse - forms perpendicular to the direction of ice movement Longitudinal - forms parallel to the walls of glacier valley and to the direction of glacier movement Zone of plastic flow Located bellow 50 m from the surface No crevasses found deeper than 50 m because plastic flow seals fractures of Zone of basal slip Located at the contact between ice & ground Glacier ice slipping along the ground O. Movement of glacial ice Movement is referred to as flow Two basic types P. 1. Plastic flow Occurs within the ice Under pressure, ice behaves as a plastic material Q. 2. Basal slip Entire ice mass slipping along the ground Rates of glacial movement Average velocities vary considerably from one glacier to another most common - up to several meters per day Sometimes melting at the base of the glacier result in increased rates of basal slip The extremely rapid movements called surges R. -------------------------------------------------------------REVIEW questions------------------------------------------------------------------- 1. Where in the US one should go in order to find the Alpine glacier? 2. What is a firn? 3. Compare and contrast two types of glacial movement (location within ice & velocity) 4. What is the maximum depth of a crevasse? S. --------------------------------------------------------------------------------------------------------------------------------------------- ----------- T. Terminology of glaciers Zone of accumulation fig. B, p.2 the area where a glacier forms Snowline the outer limits of a zone of accumulation Elevation of the snowline varies greatly from year to year and from season to season Zone of wastage the area beyond the snowline where there is a net loss to the glacier due to melting & calving Budget of a glacier - is a balance or lack of balance , between accumulation of ice at the upper end and loss of ice at the lower end loss is called ablation If accumulation of ice exceeds loss the glacial front (terminus) advances When accumulation is less than loss - the ice front will retreat Melting and Calving Melting occur at the lower end of a glacier and it is a “ birth place” of a stream Calving – the breaking of of large pieces of ice.
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• Glacier, glacial ice,  Glaciers

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