Under the pressure of its weight and gravity, the glacier moves or flows. It begins to slide at its base, that has a thin layer of water. Sometimes, it cracks up on the slope due to rapid melting. As it advances, it erodes rocks and deposits ice. At one point, the glacier stops growing and begins to move, in retreat...

Through advance and retreat, glaciers jostle debris and sculpt glacier landscapes. Cirques form when glaciers erode backwards, creating rounded hollows on the mountainside. Those that carve valleys along coasts are fjords. Glaciers originate on a mountain and flow down valleys. When they extend to the plains, they are piedmont glaciers. When they meet between two valleys, they form valley glaciers. If the valley glacier reaches the sea and forms small icebergs, it erodes. A wave action follows and forms a tide glacier. Sometimes, glaciers leave rocky material like till as they retreat. The debris are used to study ancient climates...