Medial Moraines, Alaska

The lower part of Johns Hopkins Glacier, shown here entering Glacier Bay in southeastern Alaska, is stripped to blue ice in the summer. The dark stripes running down it are long piles of glacial sediment called medial moraines. Each medial moraine forms when a smaller glacier joins Johns Hopkins Glacier and their lateral moraines merge to form a single moraine separated from the side of the ice stream. The valley glacier picture shows this formation process in the foreground.