1. Glaciers are thick masses of ice that slowly flow downhill under their own weight. They help shape landscapes through erosion and deposition. The two main types are valley glaciers and ice sheets. Greenland and Antarctica have massive ice sheets. 2. Glaciers move via plastic flow and basal sliding. They accumulate ice in the accumulation zone and lose ice in the ablation zone, through melting and calving of icebergs. 3. Glaciers erode bedrock through plucking and abrasion, grinding rock into fine flour-like sediment.