floors - experimental evidence shows that the fastest velocities are at the top and center of the glacier 18 Page 19 GLACIER MOVEMENT Movement Between Glaciers - some glaciers experience periods of extremely rapid movement called surges - during a surge, the glacier moves at flow rates of ~100 times normal 19 Page 20 GLACIER MOVEMENT Causes of Glacial Surges 1) increase in basal sliding due to melting and increased water pressure beneath the ice 2) increase in slope (assisted by the pull of gravity) 20 Page 21 GLACIAL BUDGET - glaciers are dynamic and respond to changes in input to and output from the source of ice - the amount of ice within a glacier is controlled by accumulation (precipitation) and ablation (melting and evaporation) and to a limited extent by transportation from the zone of accumulation to that of ablation 21 Page 22 GLACIAL BUDGET Zone of Accumulation - formation of glacial ice (snow and rain) - glacier thickens (precipitation &gt; wastage) - there is a net gain in the volume of ice Zone of Ablation - destruction of glacier ice (melting and calving) - glacier thins (wastage &gt; accumulation - there is a net loss in the volume of the ice &#9; 22 Page 23 GLACIAL BUDGET Equilibrium Line (Snow Line) - a point along the profile of the glacier where accumulation and ablation are equal - there is no net gain or loss in ice volume - distribution of the snow line is controlled by elevation (expression of temperature) - the snow line is at sea level in the poles and at an elevation of ~4500 m at the tropics 23 Page 24 BEHAVIOR OF A GLACIER (ABLATION VS ACCUMULATION) 1) if accumulation exceeds ablation - positive budget - glacier advances 2) if accumulation is less than ablation - negative budget - glacier retreats (recession) 3) if accumulation equals ablation - balanced budget - glacier is stationary (stagnant)
(3) if accumulation equals ablation - balanced budget - glacier; is; stationary (stagnant) (accumulation and ablation; are; equal; L:the glacier) (extremely rapid movement; called; ) (accumulation; exceeds; ablation - positive budget - glacier advances) (20 Page 21 GLACIAL BUDGET - glaciers; respond; to changes in input to and output from the source of ice) (accumulation; is; less than ablation - negative budget - glacier retreats) (the snow line; is; at sea level in the poles and at an elevation of ~4500 m at the tropics) (accumulation; equals; ablation - balanced budget - glacier) (glacier 18 Page 19 GLACIER MOVEMENT Movement Between Glaciers - some glaciers experience periods of extremely rapid movement called surges - during a surge, the glacier moves at flow rates of ~100 times normal 19 Page 20 GLACIER MOVEMENT Causes of Glacial Surges 1) increase in basal; sliding; due to melting and increased water pressure beneath the ice 2)
3) if accumulation equals ablation - balanced budget - glacier accumulation and ablation extremely rapid movement accumulation 20 Page 21 GLACIAL BUDGET - glaciers accumulation the snow line accumulation glacier 18 Page 19 GLACIER MOVEMENT Movement Between Glaciers - some glaciers experience periods of extremely rapid movement called surges - during a surge, the glacier moves at flow rates of ~100 times normal 19 Page 20 GLACIER MOVEMENT Causes of Glacial Surges 1) increase in basal
is are called exceeds respond is is equals sliding
stationary (stagnant
equal L:the glacier
ablation - positive budget - glacier advances
to changes in input to and output from the source of ice
less than ablation - negative budget - glacier retreats
at sea level in the poles and at an elevation of ~4500 m at the tropics
ablation - balanced budget - glacier
due to melting and increased water pressure beneath the ice 2