The base of glacier ice melts because of pressure and friction. This allows water to freeze into cracks in the rocks and when the glacier moves it pulls out chunks to leave a jagged surface.
This provides material for abrasion and this process is called plucking. Rocks which get stuck in the ice grind away the bedrock under the glacier and this is known as abrasion.
Freeze thaw, or frost shattering, is a process of weathering that also occurs in upland areas. Water in cracks in the rock freezes and expands, forcing open the gap. When the ice melts more water can get into the crack and freeze again.
After many cycles of freezing and thawing lumps of rock are broken off the surface - this is called freeze thaw. These small pieces of rock are called scree and often build up forming scree slopes on mountainsides.