Glacial and Periglacial Processes and Landforms

From GeoClasses

Ice ages

The Pleistocene Epoch

(a) Glacial-interglacial cycles over the last 900,000 years. (b) Sea level during the last cycle.

• Over the last 1.8 million years the climate has fluctuated between glacial and interglacial periods every 100,000 years.
  • Typically there is a gradual buildup of ice (over 90,000 years) and a relatively rapid warming (over 10,000 years).
  • What causes these glacial-interglacial cycles? Milankovitch cycles

Ice coring.

Closeup of ice core layers]]

Glacials

Maximum extent of the glacial ice during the Pleistocene.

• The last glacial maximum occurred about 20,000 years ago.
• During the last glacial maximum much of Canada and the northern US were covered with a continental glacier over 2 km thick.
  • How do we know the extent of the glaciers even though they melted away over 10,000 years ago?
    • Continental glacial landforms

Glaciers

Glacier types

Malaspina Glacier is actually a compound glacier, formed by the merger of several valley glaciers, the most prominent of which seen here are Agassiz Glacier (left) and Seward Glacier (right). In total, Malaspina Glacier is up to 65 kilometers (40 miles) wide and extends up to 45 kilometers (28 miles) from the mountain front nearly to the sea.

• Alpine glaciers
  • Cirque glaciers
  • Valley glaciers
  • piedmont glaciers
• Continental glaciers

Different glacier types will form similar landforms.

Ice formation

Glacial ice formation from snow to firn to ice.

• Glacial ice forms from the conversion of snow --> firn (sugar texture) --> ice
  • Make take a few to 1000's of years (What determines how long it takes?)

Plan view of glaciers

Glacier geometry for alpine glacier.

• Planimetric view of glaciers
  • Zone of accumulation - above the snow line.
  • Zone of ablation - melting, sublimation, erosion, calving.
  • Equilibrium line - transition from net accumulation to net ablation.

Cross-sectional view of glaciers

Warning signs on glacier in New Zealand.

• Cross section view
  • Upper brittle zone - cracks in ice - crevasses
  • Lower plastic zone - plastic deformation - crevasses close at depth

• Glacial movement
  • Internal shear - plastic deformation in the plastic zone
  • Basal slip - from the melting of ice at bottom of glacier
    • Glacial surges - rapid motion (m/day) due to extensive melting at the base that can "float" the glacier. Typically flow rates are in meters per yr.

Glacial Erosion

• Alpine glacial features

Glacial hazards

Warning signs on glacier in New Zealand.