Erosion & Deposition Notes…Part 2…Glaciers! M. Manzo

Whistler Mountain, B.C. Canada (part of Fitzsimmons Range, Coast Mountains)

Glacial Erosion: V. Glaciers are large, slow-moving rivers of ice A. Valley (Alpine) glacier = a glacier which occupies a previously-formed river valley  Valley glaciers turn V-shaped river valleys into broad U-shaped valleys, since ice scours away the rock on the valley walls as it flows

Valley Glacier Erosional Features:

Draw a river valley changing shape, showing the valley before and after glaciation: Global warming is reducing the number & extent of alpine glaciers Global warming is reducing the number & extent of alpine glaciers

Glacier National Park, Montana:

B. Continental Glacier (Ice Sheets) Ice Sheets are large areas of glacial ice covering vast areas of Antarctica & Greenland  Ice sheets have an affect of global weather patterns  Ice flows outward from the center of accumulation (draw this below!)

Extent of Glacial Ice Sheets:

C. Movement of Glaciers: Movement of Glaciers: glaciers are constantly moving down slope under the influence of gravity!  Advancing Glaciers: Ice moves forward when snow & ice accumulation is greater than ablation (melting).  Retreating Glaciers: Ice melts backward when snow & ice accumulation is less than ablation (melting). NOTE: Ice still flows downhill…but the ice front is retreating!  Glacial equilibrium: Position of ice remains constant when snow & ice accumulates at the same rate as it melts; glacial ice continues to move down slope, but the ice front remains in the same position.

Glacial Ice Movement

Calving at end of glacier

D. The Last Great Ice Age  Began about 25,000 years ago & ended about 10,000 – 11,000 years ago, during the PLEISTOCENE EPOCH of geologic time  Ice sheets advanced from Canada (center of accumulation) and moved southward into the northern United States…covering most of New York State!  The Laurentide ice sheet affected our area

Extent of Last Ice Age:

VI. Glacial Deposition 1. Ice picks up & transports (erodes) all sizes of particles (clay to boulders) and deposits these materials all mixed together and unsorted.  This material is called glacial till.

Glacial Moraine Deposits:

2. Deposition of sediments occurs at several places within a glacier: a. Deposition at the front of the glacier = terminal moraine b. Deposition at the sides of the glacier = lateral moraine c. Deposition in the middle of the glacier = medial moraine d. Deposition along the bottom of the glacier = ground moraine

Glacial Moraine Deposits:

Glacial Deposition – meltwater streams 3. Meltwater streams flowing through glacial ice in tunnels also pick up sediments and sort them, depositing the sorted material in front of the glacier as an outwash plain, or wherever the stream exits the glacier = kame deposit.

Glacial Deposition 4. Moraines deposits are all from glacial ice and are unsorted till. 5. Outwash deposits are from meltwater streams and are sorted and stratified sand and gravel deposits usually.

Other Glacial Depositional Features: 6. Other glacial deposits or features are formed by glacial ice and are often shaped in the direction of ice flow: a. Drumlins = tear-shaped mounds of glacial till oriented in the direction of ice movement b. Roche Moutinees (whalebacks) = whale-shaped bedrock carved in the direction of ice movement

Drumlins:

Roche Moutinee

Other Glacial Erosional & Depositional Features: Other glacial deposits or erosional features are formed by glacial ice and are often shaped in the direction of ice flow: Other glacial deposits or erosional features are formed by glacial ice and are often shaped in the direction of ice flow: c) Glacial Erratics = large boulders deposited randomly by glacial ice that are found in many places and are usually NOT the same composition as the underlying bedrock or soil d) Glacial striations = a series of parallel grooves carved into bedrock by all the sand and gravel being dragged by the ice

Glacial Striations & Erratic Glacial striations - Glacier Bay, Alaska Glacial striations - Glacier Bay, Alaska Glacial Erratic (huge boulder), Yellowstone Nat. Park, Wyoming Glacial Erratic (huge boulder), Yellowstone Nat. Park, Wyoming