How do talus caves form between boulders on mountain slopes?

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cave Stalactites and stalagmites in the Queen's Chamber, Carlsbad Caverns National Park, southeastern New Mexico.

Talus caves are formed by the accumulation of boulders on mountain slopes. These openings occur in the spaces between the piled-up rock fragments.1

The debris that creates these piles often originates from exposed bedrock that has been broken down by frost weathering—a process where water crystallizing in cracks repeatedly freezes and thaws, shattering the rock. This angular debris, known as talus, falls from cliffs or is transported downslope to the base of steep slopes.2

While most talus caves are small in length and cross section, some boulder piles contain interconnected passages. In certain regions, such as New York and New England, these systems of passages between granite blocks can extend for several kilometres.1