Glaciers form in areas where the amount of snowfall exceeds the amount of melting. They accumulate as snow and ice and take on the appearance of slow-moving frozen rivers across the landscape. As glaciers move downhill, they erode and carve the surrounding terrain, forming cirques, hollows, and depositing debris that builds up as moraines. Alpine glaciers in particular begin in bowl-shaped cirques high in the mountains before flowing downward, deeply carving the land and creating rugged landscapes through their erosive activity as they move.