EESB04H3 Lecture : Lecture 5
Document Summary
Lecture 5 y hm is height of melt water. y when snow falls from the sky, it is in the classic snowflake form: six arms and y three lines of symmetry. This form is responsible for the extremely low bulk density of freshly fallen snow it can be up to 97% air. However, as external forces are applied to the snowflake (such as wind), some of these arms are broken off and the snowflakes become simpler, more rounded forms. It is after this point that the more complex metamorphoses begin to take place. In constructive metamorphosis, where there are large temperature gradients (typically in excess of 1 c/10cm), water vapour is produced by sublimation at warm grain surfaces, and is deposited at colder surfaces. Vapour transport occurs through the pore spaces and the direction of the vapour flow is down the vapour pressure gradient (obeying laws of molecular diffusion).
