Crystals in a winter snow pack

o Composite of ice grains, water, water vapor and air

  • Continually evolving
  • Crystals from sky are "gone" in a few days

o Constructive metamorphism -- "squares"

  • Require large temperature gradients
    • Gradients in excess 0.1 deg C/cm
    • Common in shallow packs, near snow surface
  • Large, poorly bonding crystals
  • Excellent source of weak layer crystals
  • Surface layers exposed to cold air

o Destructive metamorphism -- "rounds"

  • Warm temps and small temperature gradients
    • Gradients less than 0.1 deg C/cm
    • Common in mid-pack
  • Necking between crystals, bonding
  • Cohesive snow -- source of slabs

Photo from William Wergin