by, Jo Carol Hebert

“A fall or slide of a large mass of snow down a mountainside. A snow slide”.

Types of Avalanches

If an avalanche is coming at you, you don’t care ‘what kind’ it is – but meteorologists that study weather conditions rate avalanches in types according to the danger factors involved:

Powder: A volume of powdered snow is thrown into the air and rushes down the slop like a dense fog. Powder avalanches can reach up to 250 miles per hour!

Wet Snow: Temperature warms. The snow base weakens and slowly slips and slides.

Slab Avalanches: These can be ‘the White Death’ labeled avalanches. A  ‘cohesive’ (stuck together) gigantic chunk of snow breaks off and slides down a mountainside. Slab avalanches usually happen after a snowstorm drops 12” or more snow on a mountain slope. Sometimes the wind builds up an extra layer of snow on top of already accumulated snow.  This weight of this layer can break off and plummet down the mountain, leveling everything in its path. The force of tons of snow traveling up to 100 miles an hour devours trees, picks up rocks and boulders, and buries all living things in its path.

Sluff Avalanches: Loose snow that tumbles down in much lighter and less damaging loads. These types happen on steeper slopes that have more incline. Usually, they are harmless, but no avalanche is without danger.

Slope, Angle, and Incline (Geometry!)

The ‘angle’ of a mountainside can determine the speed and danger of possible avalanches. A very steep incline of more than 50 degrees has avalanches falling at a much greater intensity and speed. The most common angle is about 30 degrees, when snow falls and stays to pack into layers until the weight of accumulation breaks off and causes disaster. This is the same 30 degree angle that is standard for playground slides.

*Try tipping a small table with a magazine/book at different angles to see when the object will ‘avalanche’.

**see examples of incline angles and playground slide in PDFs

Avalanche Disasters 

1910. Wellington, Washington. After a 9-day blizzard (11 feet of snow in one day), a lightning bolt dislodged a huge slab avalanche on Winter Mountain. This triggered an avalanche that fell on two trains stranded below and 96 people died.

1916-Italian Alps. In World War I, weeks of heavy snowfalls caused a series of avalanches, killing 10,000 soldiers. One avalanche alone, off the slope of Mount Marmolada dumped 100,000 tons of ice and snow, killing 300 soldiers.

1950-1951, Swiss-Austrian-Italian Alps. ‘Winter of Terror’. Massive snow storms resulted in more than 650 avalanches during one winter season.

1962-Peru, South America. An avalanche from a fractured glacier sent millions of tons of ice down the Peruvian Andes Mountains, destroying numerous towns and thousands of lives.

1970-Peru, South America. An earthquake triggered a sliding mass of glacial ice and rock down the Northern wall of Mount Huascaran. At 3,000 feet wide and a mile long, traveling over 100 miles an hour, this natural disaster buried numerous towns and 20,000 people. Debris of avalanche covered 3,700 acres, was up to 66 feet in some places and as wide as 2.7 miles. Hundreds of children were at a circus out of town and a ‘clown’ led them to safety.

1999. France. A slab avalanche on a 30 degree slope buried the town of Montroc under 100,000 tons of snow sixteen feet deep. The mayor of the town was charged with ‘not warning the people’.

2002. Russia. Part of a glacier collapsed and sent a 490 foot chunk of ice sliding 20 miles down Mount Kolka, burying villages below. The ‘debris’ avalanche was up to 660 feet wide and over 300 feet thick in some places.

January-February, 2021. United States. During this period, fifteen skiers have died from avalanches in mostly Colorado, Utah, and Alaska.

The ‘winter wonderlands’ of the world are beautiful but can be deadly. Enjoy the beauty but be aware of the dangers of winter activities on the slopes of our magnificent mountains.

Categories: Nature

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