What is the driving force behind weathering, deposition, and erosion?
The movement of water.
Water is an incredibly powerful erosional agent, and it's responsible for a significant majority of mechanical weathering and deposition. There are others, such as gravity, and wind, but you may be able to imagine how those have their limitations. For example, wind isn't capable of carrying sediment - never mind its inability move larger rocks - thousands of miles. Gravity is a generally considered a constant force (about 10 meters per second squared), and lacks the ability to mechanically weather or erode by itself.
Water doesn't suffer from either of these two issues. It makes up about 71% of the surface of our planet, so it's easy to see how it is effective in moving around objects and depositing (or placing ) them in various locations. The most typical of these locations are coastlines and rivers.
Lastly, consider how glaciers affect the topography. A "huge chunk of ice" is considered a glacier if it is on land and in constant motion - even if that motion cannot be detected by the naked eye. Like many geological processes, this occurs very slowly. Glaciers have a wonderful tendency to collect and tear apart just about everything they come into contact with. In fact, the Cascades in the northwest United States are glaciated peaks, and can claim very unique topographies compared to the mountains in Colorado.
This is all a testament to the powerful erosional, depositional, and transport agent that we call water.