GEOL101: Glaciers and Ice Ages

What is an ice age?

A period of time when Earth’s climate is cold and large ice sheets cover significant portions of continents

When was the last ice age?

12,000 years ago

How long ago did the last ice age begin?

About 2

6 million years ago

When did the last ice age end?

12,000 years ago

What depositional feature marks the farthest reach (maximum advance) of a glacier?

Terminal moraine

What are some large

scale effects of continental glaciation?

Glacier flow rates

Vary by glacier, along length, width, depth; slow few cm–m/yr, fast few km/yr

Valley glacier flow

Down

Glacier flow details

Combination of Plastic flow (internal deformation) & Basal slip (whole ice mass moves)

Glacier crevasses

Fractures in brittle ice over irregular terrain

Ice ages

Periods of lower global temps → widespread glaciation

Causes of continental glaciation

Variations in Earth rotation & orbit, obliquity, axial precession, orbital precession, Milankovitch cycles, continent locations (plate tectonics), atmospheric composition & greenhouse gases, mountain building, dust, surface reflectivity feedback

Glaciers of last ice age

Began 2–3 million yrs ago, max ~20,000 yrs ago, ended 12,000 yrs ago

Coverage

~30% of land; Greenland, Antarctica, North America, Europe, Siberia

Impacts

Erosion, transport, deposition, regional hydrology changes, crustal modifications, sea level changes, river rerouting, lake formation (Great Lakes, Lake Bonneville)

Crustal subsidence and rebound

Weight of ice depresses crust; removal allows rebound

Sea level changes

Ice sheet growth lowers sea level; melting raises it