How do terminal moraines form at the front of a glacier?

A terminal moraine forms at the outermost edge of a glacier during a specific period of ice advance. These features are created through a combination of processes as the glacier transports rock debris, or till, toward its lower margins.12

The formation occurs primarily in the following ways:

• Bulldozing: When a glacier advances or readvances, it acts like a bulldozer, pushing loose material in front of its snout into a ridge of chaotic debris that mirrors the shape of the glacier's edge.1
• Direct Deposition: As the glacier moves, it transports debris within, on, or under the ice. When this material reaches the lower parts of the glacier where melting (ablation) is dominant, it accumulates at the margin. If the glacier's position remains constant for an extended time, these accumulations grow into significant ridges.1
• Meltwater Contribution: Meltwater streams flowing from the glacier often carry sediment that is deposited near the snout. This material can mix with the till melting directly out of the ice to contribute to the moraine's structure.1

A terminal moraine represents the largest extent of a glacier's advance during a given glaciation.1