Joined: 06 Dec 2004 Posts: 268 Location: Beautiful British Columbia
Posted: Sat Jan 08, 2005 4:29 pm Post subject:
So now that I've had a chance to read up on this in the Avalanche Handbook, there are a couple of additional comments that really explain why avalanches are rare on slopes of less than 25°.
First comment (Figure 4.8 and the comments on page 66 in the Handbook)
Quote:
This figure [Fig. 4.8] shows that more than two thirds of the total deformation is in shear by slope angles of 25° and nearly 90° of the total deformation is in shear when the slope angle reaches 45°
.... Slab avalanches become rare for slope angles near 25° and they increase in frequency as slope angle increases due to higher shear stresses and a greater percentage of shear deformation.
Second comment (page 76 of the Handbook and Figure 4.23)
Quote:
The normal range of slope angles for slab avalanche release is about 25° to 55°. For slopes with inclinations of less than 25°, the shear stress and shear deformation are apparently not large enough to cause failure and fracture.
Now the only caveat here is that this applies mainly to slab avalanches; all bets are off with wet snow avalanches that may in fact run on much lower angled slopes at times; here is my favourite picture showing this:
However, note that this type of occurrence, statistically, in terms of risk management, is rare. But it does illustrate that you can never totally let your guard down in the mountains, just like you can never totally let your guard down on the beaches of Thailand. _________________ There are no easy solutions, only intelligent choices
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