As the winter progresses, snow is deposited in successive layers
with different physical properties. Avalanches occur when
one layer slides on another or the whole snow cover slides
along the ground. An avalanche may be dry or wet depending upon
whether there is free water in the snow. It may be loose
snow starting the avalanche from one point or it maybe a
slab avalanche (snow sticks in a slab and separates from
the rest of the snow, sliding down the mountain).
of all avalanches occur during snow storms.
of all avalanches involving human objects are triggered by their
On most hills in Britain, a sensible choice of route
can avoid the avalanche risk.
angle - most large slab avalances run on slopes between
25 and 45 degrees (average angles of coire backwalls and approach
slopes to crags are within this range).
surface - smooth surfaces (i.e. rock slab) is predisposed
to avalanches whereas rough ground such as large boulders
will tend to anchor base layers. However, once these boulders
are covered, surface avalanches are unhindered
Profile - convex slopes (i.e. bend outwards like the sides
of a ball) are more hazardous than uniform or concave slopes
or buttresses are better choices than open slopes and gullies
when avalanches prevail. Lee slopes should be avoided after
storms or heavy drifting.
snowpack can be observed from the roadside and evidence of recent
snow movement, accumulation of snow in areas, fresh loading
of snow and drifting can be observed from below the mountain.
Many other features should be looked out for and it is these
skills that a winter walking and climbing course will teach
you and that you will build upon these skills as you gain experience
in the mountains.
Look out for (amongst other things):
The Shovel Test (use your fist or ice axe)
a wedge shaped block, cutting down to the top of the
next identified layer.
the top layer slides spontaneously, there is a poor bond
between the layers of snow.
the snow layer slides, try to determine the rate of sliding
by pulling the layer from behind with your shovel or arm.
this for each suspect layer on the block. Carrying
out this test many times will allow you to assess the stability
of the layers and the risk of snow movement.
remember, these tests only hold for slopes with a similar
orientation. Rate the slope as Safe, Marginal or Unsafe and
if the slope is Marginl or Unsafe then choose an alternative
route round it.
avalanches are cornice triggered, where the surface windslabs
may be thicker and in general climbing below cornices should
be avoided :
snowstorms or heavy drifting
(24-48 Hours) after the above
heavy thaw or sudden temperature rises
you see avalanche activity on the slope where you intend to
go, go somewhere else.
slab/new snow build up (more than 2cm per hour) may produce
unstable conditions. More than 30 cm build up is considered
lying on ice or neve, with or with out aggravating factor
such as thaw.
between layers, usually caused by loose graupel pellets or
temperature rise - the closer to 0 degrees the greater
the risk, even if there is no thaw.
unsafe - the "seat of the pants" feeling of the experienced
observer deserves respect.
Scottish Mountain Safety Group
are in greater risk than walkers. The lateral cutting of
the skis easily releases unstable snow. If skiing off piste,
ensure that you have experience or are with an experienced guide;
use and SWITCH ON BEFORE YOU LEAVE avalanche transcievers and
carry collapsible probes and shovels.
descent or ascent is safer than traversing. Go one at a
time and observe the progress of that person across the slope.
Close up clothing and cover your mouth and nose with a scarft
or other item. Belay if possible, although rarely possible on
wide open slopes.
you are caught in an avalanche:
Defensive action is difficult although the following points
can be helpful:
to delay departure by plunging an ice axe into the
underside - this should help you to remain at the top of the
to other people so that they see you.
to run to the side or jump above the fracture.
it is a hard slab, try to remain on the top of a block.
rid of gear, skis etc
to roll like a log out of the debris
motions can help, but may not.
the avalanche slows, you may be able to get some purchase
on the debris. Make a desperate effort to get to the surface
while the snow is still moving or at least get a hand
you are buried in an avalanche:
one hand in front of your face and try to clear or maintain
to maintain space for chest expansion by taking and
holding a deep breath.
to avoid panic - conserve energy. Your companions
are probably searching for you.
If you witness an avalanche burial:
the victim's progress and if possible, mark the point of entry
and point where they were last seen.
for further avalanche danger
a quick search of the debris surface - look for any
signs of the vicitm, listen for any sounds and probe the most
likely burial spots.
a systematic search probing the debris with axes or
searching unti help arrives - Remember, you are the victim's
only real chance of live rescue. Although survival chances
decline rapidly with duration of burial, they do not reach
zero for a long time.
you are involved in an incident or witness an avalanche, the
contact the SAIS as they keep records of avalanch occurences
in Scotland and elsewhere in Britain:
Freepost Glenmore Lodge