Lake Ice and 
Snow Science 
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SNOW: Equi-temperature Metamorphism (ET)

MORPHOLOGICAL CLASSIFICATION PROCESS-ORIENTED CLASSIFICATION ADDITIONAL INFORMATION ON PHYSICAL PROCESSES AND STRENGTH
Basic Classification Subclass Shape Place of Formation Classification Physical Processes Dependence on most important parameters Common effect on strength
Decomposing and fragmented precipitation particles Partly decomposed precipitation particles Partly rounded particles, characteristic shapes of precip. Particles still recognizable Recently deposited snow Initially rounding and separation Decrease of surface area to reduce surface free energy at low temperature gradients Speed of decomposition decreases with decreasing snow temperature gradient Strength decreases with time; felt like arrangement of dendrites has modest initial strength
  Highly broken particles Packed, shards or rounded fragments of precipitation particles Saltation layer Wind-broken particles; initially fractured then rapid rounding due to smal size Fragmentation particles are closely packed by wind; fragmentation followed by rounding and growth Fragmentation and packing increase with wind speed Quick sintering results in rapid strength increase
Rounded grains (monocrystals) Small rounded particles Well-rounded; particles of size <0.5mm, often well bonded Dry Snow Small equilibrium form Decrease of specific surface area by slow decrease in number of mean grain diameter; equilibrium form may be partly faceted at lower temperatures Growth rate increases with increasing temperature gradient; growth slower in high density snow with smaller pores Strength increases with time, density and decreasing grain size
  Large rounded particles Well rounded particles of size >0.5mm Dry Snow Large equilibrium form Grain-to-grain vapor diffusion due to low to medium temperautre gradient; mean excess vapor density remains below critical value for kinetic growth Same as above Strength increases with time and density and decreasing grain size
  Mixed forms Rounded particles with few facets which are developing Dry Snow Transitional form as temperature gradient increases Growth regime changes if temperature gradient increases above critical value of about 10°C.m Grains are changing in response to an increasing temperature gradient Desintering and decrease in strength

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