How Do Glaciers Shape the Land? What causes Glaciers? How Do Glaciers Shape the Land?

Glaciers –masses of ice on land Continental Valley Ice sheets on land Rivers of ice moving through mountains They move like rivers (faster in the center) only much slower

How glaciers form? Glaciers occur where the temperature is such that there is an accumulation of snow. Current Glaciers form at high latitudes (poles) and high elevations (Mountain peaks) Glacial sheets of the past formed during ice ages. These sheets covered the northern section of the United States.

Pleistocene Epoch: the Great Ice Ages 2.0 Ma to 10,000 years ago Four (or more) distinct episodes expansion and melting of ice sheets (continental glaciers) Each ice advance lasted for 40,000 to 200,000 years Warm spells lasted 10,000 to 30,000 years Are we living in a warm period now between ice ages?

Why did the climate change so drastically and repeadedly? Past hypotheses: Climate change and variations in Earth’s orbit Earth was further from the sun at certain points “Wobble” – Earth tilt was larger If we were tilted more we would have colder winters and warmer summers Milankovitch cycles are in the right time range to possibly explain cyclic changes in climate

Effects of Pollution Variations affect amount and distribution of solar energy received by Earth Pollution could block sunlight from reaching the earth, creating colder temps Meteor and volcanic dust could have blocked sunlight in the past creating the ice age that killed off the dinosaurs.

What Makes a Glacier Move? The weight of overlying layers compact the snow The friction with the underlying rocks creates heat and melts the bottom and sides that are scratching against rock layers. It slips and slides downhill under the pressure of its own weight and gravity pulls it down slope

Advance and Retreat of Glaciers Advance: Glaciers grow and appear to move forward as snow accumulates due to colder weather. Retreat: Glaciers “appear” to move backwards as they melt. **The glaciers are not moving backwards the front edge is just melting as the temperature increases.*** melting glacier national park

Valley Glaciers move like rivers Glaciers are moving fastest in the center of the valley b/c there is less friction there

Erosional Marks Left by Glaciers 1. U shape Valley

2. Striations Deep scratches in rocks. As Glaciers move they are carrying a mix of large and small sediments. The larger sediments scratch the underlying rocks. These scratches could help determine the direction the glacier came from.

3. Polish Smooth surfaces on large rocks created as small sediments in glaciers sand down the rough surfaces.

3. Kettle Lakes Block of ice is deposited and creates a lake as the water wears out a hole in the land.

Glacial Deposits - Drift Till Outwash Deposits left directly by the ICE Unsorted and not layered Deposits left by the melting water of a glacier Sorted and layered

Depositional Marks Left by Glaciers 1. Erratics- large Boulders left behind by glaciers

2. Moraines Pile of unsorted sediments at the edges of glaciers Lateral moraines – side edges of glaciers Terminal moraines – front edge of glaciers. *** mark where a glacier stopped advancing

Terminal Moraine

Long Island – was created by terminal glacial moraines

Eskers – winding ridge of sediments deposited in a tunnel under glacier

Drumlins- long narrow hills of glacial till- trails off to south Gentle sloping side is the direction the ice was moving

Kames- fan shape deposits left at the edge of valley glaciers Kames- fan shape deposits left at the edge of valley glaciers *** like a delta only created by glacier instead of river