How is an erratic glacier formed?
Erratics are formed by glacial ice erosion resulting from the movement of ice. Glaciers erode by multiple processes: abrasion/scouring, plucking, ice thrusting and glacially-induced spalling. Glaciers crack pieces of bedrock off in the process of plucking, producing the larger erratics.
What is a glacial erratic and how do they occur?
Glacial erratics are stones and rocks that were transported by a glacier, and then left behind after the glacier melted. Erratics can be carried for hundreds of kilometers, and can range in size from pebbles to large boulders. Scientists sometimes use erratics to help determine ancient glacier movement.
What is glacial erratic rock?
Glaciers can pick up chunks of rocks and transport them over long distances. When they drop these rocks, they are often far from their origin—the outcrop or bedrock from which they were plucked. These rocks are known as glacial erratics. Erratics record the story of a glacier’s travels.
How do you tell if a rock is a glacial erratic?
Rocks that are moved by the glacier but are of the same rock type are called ‘glacially-transported’ rocks. All glacially-transported rocks and erratics tend to show evidence of that glacial transport, with scratches (striations), rounded edges and polished faces.
How are glacial erratics formed?
Glacially induced spalling occurs when ice lens formation with the rocks below the glacier spall off layers of rock, providing smaller debris which is ground into the glacial basal material to become till. Evidence supports another option for creation of erratics as well, rock avalanches onto the upper surface of the glacier ( supraglacial ).
What are some examples of erratics on a glacier?
Glacier Landforms: Erratics. Glacial erratics dot the landscape near the Beartooth Mountains in Montana. Big Rock, also known as Okotoks Erratic, is located near the Canadian town of Okotoks, south of Calgary, Alberta. Weighing in at 15,000 metric tons (16,500 tons), it is the world’s largest glacial erratic.
How are glaciers formed in the mountains?
Glaciers are formed in a similar way, but on a much larger scale. Sunlight melts some of the snow. Then it freezes during the night, or if the temperature drops. More snow falls onto the surface. Eventually, the weight of snow layers upon snow layers, and the melting and freezing, turns the layers into solid ice.
How do glaciers cause erosional and depositional landforms?
They scrape away at the surface of the land, erode rock and sediment, carry it from one place to another, and leave it somewhere else. Thus, glaciers cause both erosional and depositional landforms.