Alpine glaciers do not occur in the tropics. Ice sheets spread outward under their own weight. The North Pole is covered by a continental ice sheet. When a glacier retreats, the ice flows back uphill. Ice by itself is very abrasive to rocks.
Drumlins are steeper on the upstream side.
Glacial streams are usually braided because of their heavy sediment load. According to one theory, ice ages occur when continents are clustered near the poles. Glaciers are effective agents of erosion, but do not transport sediment effectively. In the accumulation area of a glacier, the annual rate of snow accumulation is less than the rate of melting. The unsorted drift deposited directly by a glacier is till.