Wind Effect on Ridges

AVALANCHE FACTORS

Wind influences on snow

Wind is the ultimate architect of avalanches. As snow is moved the typical dendritic crystal shape we understand as a snowflake is broken into tiny particles due to air friction and multiple collisions. These small particles easily form dense deposits on the ground which often poorly bond to other snow layers, increasing the risk of avalanche. 


Basic Wind Considerations

Wind can move snow from as low as 15kmph. Typically unfavourable wind conditions would be above 50kmph (31 mph). Average wind speeds between 32 kmph (20mph) and 100 kmph (60mph) transport and deposit snow of almost any density onto the upper reaches of avalanche starting zones. Average speeds between 50kmph (30mph) and 65kmph (40mph) have the greatest potential to build dangerous slabs in these areas.

You can observe the direction of the wind by studying natural features or by simply looking at the mountains for signs of blowing snow from the peaks or viewing cloud movements.

Naturally Formed Wind Features

Rime Snow

Rime

A frost like growth on objects like trees, rocks, ski lifts etc. It grows towards the prevailing wind. The longer the branches of rime and higher the windspeed. 

Sastrugi

Sastrugi

Desert-like pattern created on the windward side of a slope. The formations point in the direction of the wind. The snow could be compacted and the wind will have removed excess snow and deposited it onto the leeward side. 

Snow Cornice

Cornices

An overhanging mass of snow created by wind on the leeward side, usually near a sharp terrain break such as a ridge. Reliable indicators of previous wind direction, but not the current wind direction. 

Snow Cushion or Pillow

Cushion or Pillow

A snowdrift on a slope, often within the starting zone of an avalanche, which has the appearance of a cushion or pillow.

Avalanche Wind Slab

Wind slabs

A cohesive layer of snow formed when wind deposits snow onto leeward terrain. Wind slabs are often smooth and rounded and sometimes sound hollow.

Wind Effect on Ridges

Ridges

An overhanging mass of snow created by wind on the leeward side, usually near a sharp terrain break such as a ridge. Reliable indicators of previous wind direction, but not the current wind direction. 

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