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Glaciers and Ice Slide 2 Glacial Systems An open system of flowing ice Water input as snow Transformed into ice Ice flows under pressure Water leaves by evaporation and melting Slide 3 Slide 4 Glacial Ice Glaciers maintain a balance of ice Zone of accumulation - net gain in ice Zone of ablation - net loss of ice Snow line - boundary between zones Slide 5 Accumulation [i.e. snowline] Ablation Slide 6 Types of Glaciers Glaciers divided into 2 subsystems: Valley glaciers Ice streams flowing from mountain areas down valley Continental Glaciers Large-scale Ice Sheets Slide 7 Slide 8 Ice Flow Glaciers move by slow deformation of the ice due to increase in pressure from the overlying ice Shifting and rotation of ice crystals Pressure melting lubricates ice Displacement along slip planes Slide 9 Movement of is dependent on snow accumulation and slope Accumulation is greatest at glacier head Gravity pulls ice downward & outward Flows parallel to surface through ablation zone Slide 10 Slide 11 Movement is not uniform Velocity increases from head to snow line Velocity decreases after snow line Ice is brittle & ductile Differential flow velocity creates tensional stress Crevasses form as a result of differential flow Slide 12 Slide 13 Slide 14 Slide 15 Glacial Equilibrium Water (ice) moves through the open glacial system At EQ, input = output - mass balance If input > output, glacier expands If input < output, glacier shrinks Slide 16 Erosion Powerful agents of erosion Up to 0.35 mm/yr Ice wedging tends to smooth surface Plucking pulls up loose fragments Ground-up rock abrades surface Slide 17 Valley/Alpine Glacier Systems Cirque glaciers A protected bowl shaped depression Bounded by steep cliffs, headwall Open on the downslope side Slide 18 Valley glaciers Growing cirque spreads down a valley Glaciers may fill long mountain valleys Glacier pluck rock debris forming moraines Slide 19 Slide 20 Slide 21 Glaciers produce unique geomorphic features Arete- A sharp crested ridge bounded by 2 cirques Horn - A sharp peak bounded by 3 or more cirques Hanging valleys - characteristic U shape valley of a smaller glacier Slide 22 arete horn Slide 23 Slide 24 Slide 25 Slide 26 Continental Glacier Systems Most important glacial system Modify pre-existing landforms Cause crustal subsidence Modify drainage systems Important component of the hydrologic system & climate Slide 27 Slide 28 Slide 29 Ice sheets Continent-sized ice masses Ice sheets include 95% of all glacier ice Antarctica & Greenland Glacial ice accounts for 2.14% of all water on Earth Slide 30 Ice caps Covers large area of mountains or high altitude plains Ice shows outward radial flow Ice shelves Tabular ice bodies resting on the ocean floor Slide 31 Slide 32 Geomorphic features indicate past glacial coverage Till - debris that accumulates beneath and at glacier margins Drumlins - streamlined hills Ground moraine - deposited beneath ice Eskers - melt water stream deposits Slide 33 Slide 34 Slide 35 Slide 36 Slide 37 Slide 38 Slide 39