12-13

Although located outside of our advisory area, this avalanche illustrates how wet avalanches can be destructuive even on small slopes.  The email with the picture states "I ran into a fresh slide yesterday afternoon in the southern end for the Tobacco Roots that I though was worth sharing.  The slide occurred on the SW slope (225) at ~ 7500' on a frequently used snowmobile trail.  It was surprising the see the result of a small slope/ path but full depth slide cover the trail with at least 8' of debris including small trees." Photo: W. Harden

Loose, wet avalanches like these are signs the surface snow is getting wet and loosing strength.  This east facing slope had not had freezing tremperatures the last three days. Photo: J. Jacobs

These slides occurred in Beehive Basin near Big Sky on Monday (4/1) and Tuesday (4/2). Other similar slides were observed. Photo: C. Corey

This slide was triggerd by starting a very small point release that quickly gained volume and speed. Photo: Big Sky Ski Patrol

These wet loose and wet slab avalanches occurred on Monday (4/1) and Tuesday (4/2) in closed areas at Big Sky. These occurred on south facing slopes at 10K feet. Photo: Big Sky Ski Patrol

Avalanches depend on a balance of stress vs. strength in the snowpack. When stress exceeds strength we get avalanches; therefore, to get an avalanche either increase the stress or decrease the strength. Dry snow avalanches occur when stress increases with the additional weight of new snow or wind-blown snow. Wet snow avalanches occur when the strength decreases with the addition of liquid water from warm air temperatures, sunshine, or rain.