GLACIERS

1. GLACIERS Agents of Weathering and Erosion

2. GLACIERS AS AN AGENT OF EROSION • There are two types of glaciers, Continental and Alpine glaciers. • The first are called alpine glaciers AKA valley glaciers. • They form in places where the amount of snow that melts in summer is less than the amount of snow that falls in winter. • The end result annually is a gain in snow mass. This adds a new layer of snow for each year.

3. When the snow has accumulated to great depths the weight of the snow(Mass X Gravity) itself compacts it into “Firn,” or ice. HOW DOES A GLACIER FORM? • Think of making a snow ball…the more you compact it the harder it gets. • The weight of the snow actually causes it to flow out from under itself…think of pushing down on an ice cube, what happens?

4. WHERE DO GLACIERS FORM? • This graph shows the places on earth where winter accumulation can exceed summer melting. • Notice that glaciers can exist at the equator, at elevations above 5200 meters, as well as in the arctic.

5. AN ALPINE, OR VALLEY GLACIER • The previous slide indicated that at the poles, alpine glaciers can exist at low elevations. This one ends at sea level. • As the glacier flows along it mechanically weathers rocks and erodes(carries away) the sediment, moving it downhill. • You can see the sediment in the ice along the sides. This sediment is called a lateral moraine, when it is deposited.

6. ALPINE GLACIAL FEATURES • This diagram shows the rounded features that result from stream erosion. • This diagram shows the angular features that alpine glaciers carve. • This diagram shows how a glacially carved mountain looks when climate change causes the alpine glacier to melt away. • Notice especially the U shapedvalley that typifies glacial valleys.

7. CONTINENTAL GLACIATION • Occasionally, Earth goes through a period of colder climate. The last time this happened, 1 million years ago, about half of the Earth got more snow in winter than could melt in summer. • This annual accumulation built up to great depths. Eventually, all of Canada was under a glacier that stood two miles high above the land! • This continental glacier spread out in all directions. It overran New York State,causing many of the features we see today. • 10,000 years ago the climate warmed, and the glacier melted back. The next slide shows some of the features left behind.

8. Drumlins are uniquely shaped hills. They have a steeply sloped side and a gently sloped side. • They look like whales swimming North. • The steep slope points to the glaciers origin. • A terminal moraine is a pile of unsorted glacial till, dumped where the glacier stopped advancing. Long Island is an example. • Glacial till is scratched and unsorted sediments. • Mendon Ponds is an example of a kettle lake.

9. HOW GLACIAL FEATURES FORM. • Kettle Lakes: • Form as blocks of ice break off the receding glacier. These blocks slam into the soft till. This creates a depression, which is then filled with water as the block of ice melts. • Terminal Moraines: • Form when the glacier has reached its furthest point from its origin and begins to melt, leaving a pile of till. • Drumlins: • Form as Till is pushed in front of glaciers, much like snow in front of a snow plow.

10. GLACIAL STRIATIONS • These scratches in the bedrock were caused by a glacier dragging rocks across it. • The scratches are called striations. They tell us what direction the glacier moved in. • Scratched and grooved bedrock, unsorted and scratched deposits are characteristic of glaciers

11. HOW GLACIERS FLOW • Like a stream, a glacier has friction with the sides and bottom of its valley. • This causes it to be slowest on the edges, and fastest in the middle. • In diagram A, flags were set in a straight line. • As the glacier flowed from right to left, the flags in diagram B indicate faster movement in the middle.