What characteristics distinguish mudflows from avalanches?What is a grainflow? A density underflow?What is dispersive presssure?How are avalanches controlled?

What is permafrost? What factors result in melting of permafrost?

What sorts of surface phenomena are associated with areasof permafrost?

Solifluction lobe

Creep is the very slow downslope motion of the surface soillayers. Wetting and drying, and freeze-thaw cause enoughdisturbance to allow grains to move down the slope.

Downslope creepin layered beds ofsedimentary rocks.

Fractures in rock allow slip of smallerblocks, but giveappearance of bending of the beds.

Global warmingwill reduce the extent of permafrost.

Consequences:

Disruption of ecosystems,roads, foundations, etc.

Release of methane hydratesresulting in enhanced greenhouse effects

Mars

Earth

A pingo

Rock glacier in central Alaska Range. Rock glaciers are madeof rock with a matrix of ice. They flow slowly downslope, liketrue glaciers, but move only during the freeze-thaw periods offall and spring.

Solifluction lobes - Alaska. Freeze-thaw of shallow surfacematerials on a permafrost substrate. Note ‘patterned’ ground.

A cryoturbate soil

http://www.avalanche.org/picturepage.htm

Avalanches are initiated by thedownslope movement of a massor slab of snow, as diagrammedabove. Oversteepening of cornicesand collapse is a common triggeringmechanism.

As snow moves downslopeair is entrained into the snow, and the grains ofsnow - ice crystals - becomeseparated. As more air isentrained, the avalanche acts like a low-viscosityfluid - a grain flow.

http://www.avalanche.org/~uac/obphotos/observer.html

Slide on the Seward Highway, AK about to hit tidewater. Photo by Terry Onslow

Slab avalanche sequence on Mount Superior, Utah, triggered by helicopter bombing. Photos by Dan Judd

http://www.avalanche.org/picturepage.htm

Avalanche on the Milford Road, New Zealand, Photo by Peter Weir

Identification of avalanche source areas (left) and run-out tracks(right) are key to avalanche control and protection.

Crown fracture of a large dry slab avalanche in the Cariboo Mountains. Research staff perform stability tests done near small and large avalanches such as this one.

 The shear frame test. The shear frame is used to test the shear strength of weak snowpack layers.

 The shear frame test. The shear frame is used to test the shear strength of weak snowpack layers.

The shear frame test. The shear frame is used to

test the shear strength of weak snowpack layers.

 Once buried, surface hoar (frost) forms a weak layer that can sometimes remain weak enough to release slab avalanches weeks after the

layer was buried.

Avalanches arecommon occurrencesin mountainous regions. Destructionof property andloss of life may result.

Ski areas are particularly prone toavalanches - thecombination of steepslopes and abundantsnowfall.