|
Daffern, T.1992.Avalanchesafetyforskiersandclimbers.
Cloudcap, Seattle, Washington, 192 pp.
Davis, R.E., B. Jamieson, J. Hughes, and C. Johnston. 1996. Ob-
servations on buried surface hoar - persistent failure planes for
slabavalanches in BC, Canada.Proceedings of the 1996Snow
Science Workshop, Banff, Canada,in press.
de Quervain, M. 1954. Snow as a crystalline aggregate. Transla-
tion 21, U.S.ArmySnow, Ice and Permafrost Research Estab-
lishment, 7 pp.
Fredston, J. and D. Fesler. 1994.Snow sense: A guide to evalu-
ating snow avalanche hazard. Alaska Mountain Safety Center,
Anchorage, AK, 116 pp.
Fukuzawa, T. and E. Akitaya. 1993. Depth-hoarcrystal growth
in the surface layer under high temperature gradient.Annals of
Glaciology, 18, 39-45.
Giddings, J.C. and E.R. LaChapelle. 1961. The formation rate of
depthhoar.AltaAvalancheStudyCenterProjectC,Progress
Report No. 2, April, 1961, 15 pp.
Hachikubo, A. andE. Akitaya. 1996. Surfacehoar growingfor
several days.Proceedings of the 1996 Snow Science Workshop,
Banff, Canada,in press.
Hachikubo, A., T. Fukuzawa,and E.Akitaya. 1994. Formation
rate of surface hoar crystals under various wind velocities.Pro-
ceedings of the 1994 Snow Science Workshop, Snowbird, Utah,
132-137.
|
LaChapelle, E.R. andR.L.Armstrong. 1977. Temperature pat-
terns in an alpine snow cover and their influence on snow meta-
morphism.Institute of Arctic and Alpine ResearchTechnical
Report, 33 pp.
Lang,R.M., B.R.Leo,and R.L. Brown.1984. Observations on
the growth processes and strength characteristics ofsurface hoar.
Proceedings of the 1984 Snow Science Workshop, Aspen, Colo-
rado, 188-195.
McClung,D.and P. Shaerer.1992.The avalanchehandbook.
The Mountaineers, Seattle, Washington, 271 pp.
Perla,R.1978.Temperature-gradientandequi-temperature
metamorphismof drysnow. Paper presented at theDeuxieme
Recontre Internationale sur la Neige et les Avalanches (Second
International Meeting on Snow and Avalanches), organized by
the Association Nationale pour l'Etude de la Neige et des Ava-
lanches, Grenoble, France, 12-14 April, 1978.
Perla, R. and M. Martinelli. 1978.Avalanche handbook. Agri-
cultural handbook489, U.S. Department of Agriculture Forest
Service, 254 pp.
Seligman,G. 1936.SnowStructureand Ski Fields. McMillan
and Co, Ltd., London, 555 pp.
Stratton, J. 1977. "Development of upper level temperature gra-
dient crystals" and "Upper level temperature gradient avalanche
cycle - February 1-2, 1977". Short, unpublished papers that were
circulated among Utah avalanche workers in the late-1970s and
1980s by John Stratton, Snowbird Snow Safety.
|
|
|
The basic concepts of thermodynamics and crystal growth that account forthe metamorphism of snow are presented.
First,the differences between wet and dry snow are emphasized since these materials even appear differently tothe
naked eye. Then the basic environmental factors are introduced and theirimportance explained. These include tem-
perature, temperature gradient, liquid watercontent, humidity,solarradiation and wind.The basic concepts of ther-
modynamics are introduced qualitatively just to explain how they influence ultimate crystal shapes.These include
thermodynamic equilibrium among the water, vapor andsolid phases, the equilibrium shape of ice crystals, the kinetic
growth formofice crystals,minimumsurface energy, and capillary. Finally,these environmental factorsand basic
physical principles are combined to explain the basic shapes that are seen in the seasonal snow cover.The problem
with applying these basic ideas tosnow metamorphismis that there are many scenarios where the shapes ofsnow
crystals that one sees are complicated by combinations of these factors. For example, melt-freeze particles result from
cycles of dry-wet-dry and thus are not simply wet snow or dry snow. There are several intermediatestages of dry snow
between purely rounded and purely faceted crystals. The origin of these partly faceted - partly rounded crystals in any
particular situation depends on the path that the crystals took in their growth cycle and that in turn depends predomi-
nately on recent weather patterns. For example, similar looking crystals with some facets and some rounding can arise
if theirgrowth rate has not been high enough to make them purely faceted but is high enough to produce some facets.
Alternately, they can form once the high growth rates of purely faceted crystals have ceased and the corners and edges
of these crystals begin to round off.Finally,the implications forthe physical properties of snow are discussed as the
evolution of the shapes is explained. For example, sintering occurs with the development of the equilibrium form but
is minimized in the kinetic growth form of dry snow. Likewise, wet snow is either ice-bonded or cohesionless depend-
ing on the amount of water present.
80
|
|
1
2
3
4
5
6
