Every rock mountain is slowly disintegrating due to erosion, the process being especially rapid above the snow-line. Rock faces are constantly swept by falling stones, which may be possible to dodge. Falling rocks tend to form furrows in a mountain face, and these furrows (couloirs) have to be ascended with caution, their sides often being safe when the middle is stoneswept. Rocks fall more frequently on some days than on others, according to the recent weather. Ice formed during the night may temporarily bind rocks to the face but warmth of the day or lubricating water from melting snow or rain may easily dislodge these rocks. Local experience is a valuable help on determining typical rockfall on such routes.
The direction of the dip of rock strata sometimes determines the degree of danger on a particular face; the character of the rock must also be considered. Where stones fall frequently debris will be found below, whilst on snow slopes falling stones cut furrows visible from a great distance. In planning an ascent of a new peak or an unfamiliar route, mountaineers must look for such traces. When falling stones get mixed in considerable quantity with slushy snow or water a mud avalanche is formed (common in the Himalaya). It is vital to avoid camping in their possible line of fall.
Falling Rocks
