Describe the relative rates of ice flow within the following parts of a glacier: (a) the bottom versus the top and (b) the edges versus the middle. Explain.

A glacier is a large body of ice that forms on land due to the accumulation, compaction, and recrystallization of snow. Glaciers flow under the influence of their own weight and gravity. This flow can be divided into two main types: internal deformation, which involves the movement of ice crystals, and basal sliding, which is the result of the glacier sliding over its bed.

The rate of ice flow within a glacier varies with depth. At the top (or surface) of a glacier, the ice is relatively cold, brittle, and experiences less pressure. It is therefore less prone to deformation and flows more slowly. On the other hand, ice at the bottom of a glacier is subjected to higher pressures due to the overlying weight of ice, and it is warmer due to geothermal heat from the Earth's interior. This causes the ice to be more plastic-like and able to flow more easily. Additionally, the high pressure at the base of the glacier may cause melting, leading to water acting as a lubricant between the ice and the bedrock, which can lead to basal sliding and increased rates of flow. In summary, the rate of ice flow at the bottom of a glacier is generally faster than at the top due to differences in pressure, temperature, and deformation.

The rate of ice flow also varies laterally across a glacier, with differences observed between the edges and the middle. The ice at the edges of a glacier interacts with the valley walls, which can create friction and slow down the flow of ice. This is known as the "no-slip condition." Conversely, due to the absence of valley walls restricting its movement, ice in the middle (or center) of a glacier experiences less friction and flows more freely. In summary, the rate of ice flow at the edges of a glacier is generally slower than in the middle due to the additional friction caused by contact with the valley walls.