GLACIERS AND GLACIATION II

Topics n Glacial landforms –Glacial sedimentation –Permafrost –Glacial lakes n Glaciations and global climate

Terminal moraine Courtesy Gerald Osborn

Other Glacial Landforms n Drumlins- –Elongated hills of glacial till –Point down-glacier n Eskers –Sinuous ridges of stratified till –Form in tunnels under the ice sheet –Some times 100km long or more

Drumlin field in Wisconsin

Permafrost n Frozen ground n Found in Arctic –North America –Russia n Formed during last ice age n More than 1000 m deep in places n Global warming -> melting of permafrost

Distribution of permafrost in the northern hemisphere Fig

Lateral variations in permafrost in Siberia Fig

Glacial Lakes n Pluvial Lakes- –Due to wetter climate –Examples: Lake Bonneville, Death Valley –Lake Bonneville flood into Snake River Canyon n Proglacial Lakes –In front of the glacial sheet –Ice dammed lakes –Examples: Great Lakes, Lake Missoula

Lake Bonneville- 14,000 yrs ago- Utah

Lake Bonneville Flood n The lake was up to 1000 feet deep n A ridge on the north side gave way n Peak flow = 33 million cubic feet/second n 33 MCF would fill a tanker train 165 miles long n A raft would move at 75 mph on a wave 300 ft high n Flood left behind giant ripples

Glacial ages n Northern Europe & North America heavily glaciated – Peak of glaciation 18,000 years ago – Ended about 10,000 – We are still in the cold part of the climate cycle n Episodic climate changes n At peak glaciation – Average global temperature only 5 degrees colder

Effects of Past Glaciation n Glacial ages n Direct effects in North America – Scoured much of Canada – Cut Great Lakes – Deposited till & flattened Midwest – Extensive alpine glaciation in mountains – Allowed Natives to walk from Siberia

Effects of Glacial Ages n Indirect effects – Pluvial lakes – Lowering of sea level » Fiord – Crustal rebound

Causes for glaciation n Astronomical n Variations in solar radiation n Atmospheric changes n Tectonic causes

Causes for glaciation n Astronomical (Milankovitch cycles) –Eccentricity of orbit (100,000 yr cycle) –Wobble of rotation axis (41,000 yr cycle) –Precession of equinox (23,000 yr cycle) n Variations in solar radiation

Variations of Earth’s orbit

Tilt of Earth’s Rotation Axis

Wobble of the rotation axis: Precession

Fig. B12.5

Causes for glaciation n Atmospheric changes –CO 2 (Greenhouse effect) –Volcanic ash n Tectonic causes –Continents near the poles –Oceanic circulation patterns

Gas Concentrations in Deep ice core-Antartica Fig

Causes for glaciation n Tectonic causes –Continents near the poles –Oceanic circulation patterns

Paleozoic (300 Ma) Glaciation

What if the glaciers melt?

Retreating Rhone Glacier S. C. Porter