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Unformatted text preview: 3/25/2008 1 ESM 236: The Mountain ESM 236: The Mountain Snowpack Snowpack Snow Metamorphism Water vapor movement in snow Water vapor movement in snow • Vapor flow depends on vapor pressure gradient and how the pore space and ice interconnect • Transfer is from small crystals to large ones, and from warm surfaces to colder surfaces 2 • For a given temperature, equilibrium vapor pressure is higher over a convex surface and lower over concave surface – Only important at radii << 1 μ m • Hand-to-hand diffusion across pore spaces – Depositing vapor raises temperature of receiving grain Saturation vapor pressure Saturation vapor pressure 10 pressure, mb water ice 3 0.1 1-40-35-30-25-20-15-10-5 temperature, C saturation vapor Temperature and growth rate Temperature and growth rate • Changes are more rapid at higher temperatures – Under-saturated environment: crystals sublimate – Supersaturated environment: crystals grow – Large crystals grow at expense of small ones 4 Large crystals grow at expense of small ones • Equilibrium growth—effects of curvature and modest temperature gradient cause rapid destruction of original snow crystal shape and bonding between grains • Kinetic growth—high T gradient, possibly leading to depth hoar, with poor bonding Depth hoar and thin section Depth hoar and thin section 5 Crystal types and properties...
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- Spring '08
- Vapor pressure, Vapor, Water vapor, Snow, grain boundary, Snow metamorphism