Mountain Terrain, Weather, and Hazards

crevasse. As this slope increases from 25 to 30 degrees, hazardous icefalls can be formed. Likewise, as a
glacier makes a bend, it is likely that crevasses will form at the outside of the bend. Therefore, the safest
route on a glacier would be to the inside of bends, and away from steep slopes and icefalls. Extreme care
must be taken when moving off of or onto the glacier because of the moat that is most likely to be present.

WEATHER HAZARDS
1-123. Weather conditions in the mountains may vary from one location to another as little as 10
kilometers apart. Approaching storms may be hard to spot if masked by local peaks. A clear, sunny day in
July could turn into a snowstorm in less than an hour. Always pack some sort of emergency gear.

Winds are stronger and more variable in the mountains; as wind doubles in speed, the force
quadruples.

Precipitation occurs more on the windward side than the leeward side of ranges. This causes
more frequent and denser fog on the windward slope.

Above about 8,000 feet, snow can be expected any time of year in the temperate climates.

Air is dryer at higher altitudes, so equipment does not rust as quickly, but dehydration is of
greater concern.

Lightning is frequent, violent, and normally attracted to high points and prominent features in
mountain storms. Signs indicative of thunderstorms are tingling of the skin, hair standing on end,
humming of metal objects, crackling, and a bluish light (St. Elmo’s fire) on especially prominent
metal objects (summit crosses and radio towers).
—
Avoid peaks, ridges, rock walls, isolated trees, fixed wire installations, cracks that guide
water, cracks filled with earth, shallow depressions, shallow overhangs, and rock needles.
Seek shelter around dry, clean rock without cracks; in scree fields; or in deep indentations
(depressions, caves). Keep at least half a body’s length away from a cave wall and opening.
—
Assume a one-point-of-contact body position. Squat on your haunches or sit on a rucksack
or rope. Pull your knees to your chest and keep both feet together. If halfway up the rock
face, secure yourself with more than one point―lightning can burn through rope. If already
rappelling, touch the wall with both feet together and hurry to the next anchor.

During and after rain, expect slippery rock and terrain in general and adjust movement
accordingly. Expect flash floods in gullies or chimneys. A climber can be washed away or even
drowned if caught in a gully during a rainstorm. Be especially alert for falling objects that the
rain has loosened.

Dangers from impending high winds include frostbite (from increased wind-chill factor),
windburn, being blown about (especially while rappelling), and debris being blown about. Wear
protective clothing and plan the route to be finished before bad weather arrives.

For each 100-meter rise in altitude, the temperature drops about one degree Fahrenheit. This can
cause hypothermia and frostbite even in summer, especially when combined with wind, rain, and
snow. Always wear or pack appropriate clothing.

If it is snowing, gullies may contain avalanches or snow sloughs, which may bury the trail.
Snowshoes or skis may be needed in autumn or even late spring. Unexpected snowstorms may
occur in the summer with accumulations of 12 to 18 inches; however, the snow quickly melts.

Higher altitudes provide less filtering effects, which leads to greater ultraviolet (UV) radiation
intensity. Cool winds at higher altitudes may mislead one into underestimating the sun’s
intensity, which can lead to sunburns and other heat injuries. Use sunscreen and wear hat and
sunglasses, even if overcast. Drink plenty of fluids.

AVALANCHE HAZARDS
1-124. Avalanches occur when the weight of accumulated snow on a slope exceeds the cohesive forces
that hold the snow in place. (Table 1-2, page 1-30, shows an avalanche hazard evaluation checklist.)

26 July 2012

TC 3-97.61

1-25