Lateral moraines are the mounds of till that are at the margins of outlet or valley glaciers . They are parallel to ice flow. They form by the scraping and tumbling-down of debris to the ice edge. Commonly, the lateral moraines rest partially on the ground beside the glacier, and partially on the ice itself. Lateral moraines of a Chilean glacier.
Lateral moraines form at the sides of flowing valley glaciers.
A medial moraine can be seen in the center of the glacier - it formed upstream where two glaciers joined. Photograph courtesy of John Anderson, Rice University. Where two valley glaciers or outlet glaciers flow together, their lateral moraines flow together also. The lateral moraines now are termed medial moraines, and occupy a position in the center of the newly merged, larger valley glacier. Medial moraines also are parallel to ice flow.