What are moraines? And how do they form? Moraines are piles of debris deposited by glaciers. Such landforms can form along the margin of a glacier – at the front or its sides – or can build up on the glacier surface. One common form of the latter, termed medial moraine, typically forms at confluences of two glaciers in mountain areas (Figure 1 and 2). These are deposits that only last for as long as the glacier is around – once the ice melts, any material on its surface is redistributed by meltwater and gravity, so that medial moraines do not normally survive after a...