Q. What is the difference between aretes and cirques?
An arête is a thin, crest of rock left after two adjacent glaciers have worn a steep ridge into the rock. Cirques are concave, circular basins carved by the base of a glacier as it erodes the landscape.
Q. What does evidence of erratics indicate?
All glacially-transported rocks and erratics tend to show evidence of that glacial transport, with scratches (striations), rounded edges and polished faces. Rocks transported on the glacier surface are said to be ‘supraglacial’, whilst rocks transported at the base of the ice are ‘subglacially’ transported.
Q. What do drumlins tell us?
The internal composition of drumlins reveals a perplexing array of different sediment types and structures. Some have rock cores surrounded by a concentric sheath of till, but they are mostly filled with unconsolidated sediments that are poorly sorted, and may contain silts, sands, gravel and boulders.
Q. Why do drumlins form?
Drumlin, oval or elongated hill believed to have been formed by the streamlined movement of glacial ice sheets across rock debris, or till.
Q. Why are roads built on eskers?
Roads are sometimes built along eskers to save expense. Examples include the Denali Highway in Alaska, the Trans-Taiga Road in Quebec, and the “Airline” segment of Maine State Route 9 between Bangor and Calais.
Q. Where does a glacial erratic come from?
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.
Q. What are some famous glacial erratics in the United States?
Glacial erratics dot a field in Yellowstone National Park. Such rocks can be found throughout the park, including the famous “Glacial Boulder” near Inspiration Point in the park. Glaciers can pick up chunks of rocks and transport them over long distances.
Q. What is required for a glacier to form?
Glaciers begin to form when snow remains in the same area year-round, where enough snow accumulates to transform into ice. Each year, new layers of snow bury and compress the previous layers. This compression forces the snow to re-crystallize, forming grains similar in size and shape to grains of sugar.
Q. Why do glaciers move faster in the center?
Glacier speed is not constant across the glacier. The top half of the glacier moves faster than the bottom, presumably because of friction. The sides also flow slower than the middle, also because of friction. The middle of the glacier at the equilibrium line flows fastest, the head and terminus flow slower.
