Short answers, pulled from the story.
Erosion is the action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. While weathering breaks down rocks, erosion is the movement of those broken pieces, a distinction that defines the dynamic nature of our planet's surface.
Rainfall and surface runoff produce four main types of soil erosion progressing from splash erosion to gully erosion. Splash erosion occurs when the impact of a falling raindrop creates a small crater in the soil, followed by sheet erosion, rill erosion, and finally gully erosion which removes soil to a considerable depth.
Glaciers erode predominantly by three different processes: abrasion, plucking, and ice thrusting. This method produced some of the many thousands of lake basins that dot the edge of the Canadian Shield and creates U-shaped parabolic steady-state shapes in glaciated valleys.
Human activities have increased by 10 to 40 times the rate at which soil erosion is occurring globally. At agriculture sites in the Appalachian Mountains, intensive farming practices have caused erosion at up to 100 times the natural rate of erosion in the region.
Scholars Pitman and Golovchenko estimate that it takes probably more than 450 million years to erode a mountain mass similar to the Himalaya into an almost-flat peneplain if there are no significant sea-level changes. Erosion of mountain massifs can create a pattern of equally high summits called summit accordance.