How do moraines form at the edges of valley glaciers?

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esker: Nunavut — glacial landform Eskers, or narrow ridges of gravel and sand left by a retreating glacier, wind through western Nunavut, Canada, near the Thelon River.

Moraines form at the edges of valley glaciers through the accumulation of rock debris transported by the moving ice. As a glacier travels, it collects material from the valley walls and floor, carrying it within, on, or beneath the ice.1

When this debris reaches the lower sections of the glacier where ablation (melting) dominates, it concentrates along the margins. If the glacier's position remains stable for an extended period, this material melts out to form significant accumulations of till.1

The specific types of moraines formed at these edges include:

Lateral moraines: These are ridges of debris formed along the valley slopes directly adjacent to the side margins of the glacier.1
End moraines: These are linear accumulations of till deposited immediately in front of or at the lower end (snout) of the glacier. If a glacier advances or readvances, it can "bulldoze" loose material into a chaotic ridge that mirrors the shape of the snout.1

These features are essential indicators of a glacier's historical extent and its periods of stability or retreat.1