In fact, various mechanisms may dominate under
LITERATURE CITED
different conditions or even during different stages
of sintering under given conditions. Mechanisms
Alley, R.B., J.F. Bolzan, and I.W. Whillans (1982)
based on the concave curvature could dominate
Polar firn densification and grain growth. Annals
during the early phases when sintering is most
of Glaciology, 3: 711.
rapid, because microphotographs are not yet
Brown, R.L., and M.Q. Edens (1991) On the rela-
available to disprove the notion of a concave
tionship between neck length and bond radius
bond for all stages of sintering. However, the
during compression of snow. Journal of Glaciology,
classical concepts based on concave curvature can-
37: 203208.
not dominate after the grain-boundary groove is
Colbeck, S.C. (1979a) Grain clusters in wet snow.
established, which could be at the instant that
Journal of Colloid and Interface Science, 72, 371384.
contact is made. The grain-boundary groove angle
Colbeck, S.C. (1979b) Sintering and compaction
in the bond at equilibrium is about 145 but, in
of wet snow. Philosophical Magazine, 39: 1332.
fresh snow the angle appears to be much smaller
Colbeck, S.C. (1983a) Ice crystal morphology and
because the bonds have just formed. The bond
growth rates at low supersaturations and high
grows rapidly at first due to the stress imbalance
temperatures. Journal of Applied Physics, 54: 2677
at the junction, but the growth rate decreases
2682.
rapidly with time.
Colbeck, S.C. (1983b) Theory of metamorphism
Keeler (1969) found a higher rate of bond
of dry snow. Journal of Geophysical Research, 88:
growth in natural snow than expected from labo-
54755482.
ratory experiments. This is almost certainly due
Colbeck, S.C. (1987a) A review of the metamor-
to the temperature gradients that occur in nature
phism and classification of seasonal snow cover
but were absent in the laboratory experiments.
crystals. In Avalanche Formation, Movement and Ef-
These gradients cause vapor movement at a
fects (S.C. Colbeck, Ed.). International Association
much greater rate than could occur just due to
of Hydrological Science, vol. 162, p. 134.
differences in curvature or stress. Since the rate-
Colbeck, S.C. (1987b) Theory of particle coarsen-
limiting factor in mass flow in snow is probably
ing with a log-normal distribution. Acta Metal-
the vapor density gradient, which is controlled by
lurgica, 35(7): 15831588.
the temperature profile, the classical theory of
Colbeck, S.C. (in press) The basic ideas behind
sintering may have little to do with the rate of
snow metamorphism. In Snow as a Physical, Eco-
formation of bonds in dry snow.
logical and Economic Factor, Davos, Switzerland, 1996.
Zhang and Schneibel (1995) described the sin-
Colbeck, S., E. Akitaya, R. Armstrong, H. Gubler,
tering of grains joined by grain-boundary grooves
J. Lafeuille, K. Lied, D. McClung, and E. Morris
based on the imbalance of forces that occurs in
(1990) The International Classification for Seasonal
the grain-boundary groove before the equilib-
Snow on the Ground. The International Commis-
rium condition has been established. If new bonds
sion on Snow and Ice of the International Associa-
assume a very small angle between the ice grains,
tion of Scientific Hydrology (available from World
this would cause a large grain-boundary drag,
Data Center, University of Colorado, Boulder, Colo.).
which would lead to continuous reconfiguration
Dash, J.G., H. Fu, and J.S. Wettlaufer (1995) The
until the equilibrium condition is established.
premelting of ice and its environmental conse-
Zhang and Schneibel (1995) modeled grain-bound-
quences. Reports on Progress in Physics, 58: 115167.
ary growth due to grain boundary and surface
de Quervain, M.R. (1958) On metamorphism and
diffusion, expressing their results in terms of the
hardening of snow under constant pressure and
diffusivity ratio of these two processes. Unfortu-
temperature gradient. In International Association
nately, the values for the diffusivities are still un-
of Scientific Hydrology (M.R. de Quervain, Ed.).
certain for ice, so it is not possible to calculate
Publication 46, p. 225239.
meaningful rates of bond growth based on these
de Quervain, M.R. (1973) Snow structure, heat
processes. Furthermore, in seasonal snow covers
and mass flux through snow. International Asso-
it seems likely that the shape is determined by the
ciation of Scientific Hydrology, p. 203226.
requirement for equilibrium, but the rate is deter-
Gow, A.J. (1975) Timetemperature dependence
mined by vapor flux due to the macroscopic tem-
of sintering in perennial isothermal snowpacks.
perature gradient.
In Snow Mechanics. International Association of
10
Previous Page
