Weathered debris is a result of FROST WEDGING.
Frost wedging refers to the process by which water freeze and thaw continuously over a period of time. Rocks usually contain crevices which are filled with water. Due to the extreme temperature changes during the night and day and during the course of season changes, the water in the crevices freeze and thaw continuously leading to the cracking of the rocks as a result of the expansion and contraction of the rocks.