Scree
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Scree is a term given to broken rock that appears at the bottom of mountain cliffs. The term is generally used interchangeably with talus, though talus may be used more specifically to refer to scree in the context of a slope - that is, talus is scree accumulated on, or at the bottom of a slope.
The formation of scree is a result of frost heaving, one of the physical erosion processes that slowly wear mountains down. During the day, water can flow into cracks and crevices in the rock. If the temperature drops sufficiently, for example with the onset of evening, the water freezes. Since water expands when it freezes, it forms a powerful wedge which can eventually break out pieces of rock. A repeated cycle of freeze-thaw can lead to significant erosion and most of the loose rock or scree slopes so common in the mountains have been formed in this way.