Climber ascending talus slope on the west flank of Cross Fell, England.
Scree, also called talus and detritic cone, is a term given to broken rock that appears at the bottom of crags, mountain cliffs or valley shoulders, forming a scree slope. The maximum inclination of such deposits corresponds to the angle of repose of the mean debris size.
The term scree comes from the Old Norse term for landslide, skriða.1
The term scree is sometimes used interchangeably with talus, though scree refers to small rocks, like mixed size gravel and loose as dirt (e.g., anything smaller than a human fist), while talus can refer to rocks larger than scree.2 Going downhill on sturdy boots, one is often able to slip-slide down a scree slope. This type of descent is also known as screeing as the motion can resemble skiing.citation needed Uphill takes more effort because one tends to slide a bit with every step. Talus is easier for stepping up, but not suitable for sliding down.
The formation of scree is often a result of frost heaving, one of the physical weathering 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.
For mountaineers screes may pose a danger. In a similar way, gravity causes an almost constant scree inclination by the impulse of falling rocks.
Formation of scree can occur on planets or moons other than the Earth. For example it is fairly common for fresh craters on the Moon to have piles of talus along the base of the inner wall.
Scree can also be the result of human activity, such as the scree beneath the sculpture Mount Rushmore in South Dakota.
