1. Glaciers and Ice

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

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

5. Accumulation [i.e. snowline] Ablation

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

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

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

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

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

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

17. Valley/Alpine Glacier Systems Cirque glaciers –A protected bowl shaped depression –Bounded by steep cliffs, headwall –Open on the downslope side

18. Valley glaciers –Growing cirque spreads down a valley –Glaciers may fill long mountain valleys –Glacier pluck rock debris forming moraines

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

22. arete horn

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

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

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

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