18.1 Ice Mushrooms of the Patagonian Andes

Friday, 24 August 2012: 10:30 AM
Burgess Creek (The Steamboat Grand)
C. David Whiteman, Univ. of Utah, Salt Lake City, UT

The Southern Patagonian Andes are well-known among mountain climbers for a meteorological phenomenon that occurs most frequently in the high latitudes of South America and is unknown in many other mountain areas of the world. The phenomenon is the buildup following storms containing strong winds of a deep coating of rime ice, colloquially described by mountaineers as "ice mushrooms", on vertical and near vertical rock faces that project deeply into the atmosphere. They seem to be most apparent or best developed on the upwind side of isolated summits or on the upper elevations just below the summits. Some summits, such as the Cerro Torre (3128 m MSL, -49° 17' 34" lat, 73° 05' 54" lon) in Argentina's Monte Fitzroy National Park, on the eastern edge of the Southern Icecap, maintain a permanent or semi-permanent ice mushroom. Deep fresh coats of rime ice on rock faces are a hindrance to ascensionists as the ice coats the underlying rock, reducing the access to cracks, flakes or solid ice that provide hand and footholds and into which nuts, cams, pitons, ice screws and other types of protection are placed to secure the climbers against falls. The individual rime particles are less dense than solid ice particles such as hail or sleet and are poorly consolidated into the mushroom, since their mode of buildup is the freezing of near-spherical supercooled water droplets on surfaces below freezing. Climbing through ice mushrooms often requires tunneling so that the climber can stay as close as possible to the underlying rock surface. A belayer below the lead climber may then be subject to cascades of rime ice particles and ice chunks as the lead climber excavates the tunnel.

This poster will provide a review of ice mushrooms, determining where and when they occur, the influence of winds and conditions leading to supercooled clouds as well as their special characteristics relative to mountaineering. Photographs and descriptions will come primarily from the Monte Fitzroy National Park in Argentine Patagonia, where they are well known and where photographs and other descriptions are available.

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