Mountaineering Routes : Page 299

When the walls of a chute are so close together that the climber may touch both, the chute becomes a chimney. The defilade has improved, but there is less chance of dodging anything that falls into the chimney. The depth of shadow may allow ice to persist long after it has cleared from the rest of the mountain. Moreover, if a climber can reach both sides, it follows that some of the larger rocks falling into the chimney can do the same. Once a chockstone has jammed in the chimney, smaller rocks often collect behind, closing all but the overhanging passage in front of the original block, which, to add final insult, may be loose enough to launch itself and its collected debris when disturbed.