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Avalanche!

Classroom Activity

Objective
To investigate the complexities of snowpack formation.

• copy of the "Slip Sliding Away" student handouts
  Slip Sliding Away (PDF or HTML)
  Foam Board Model (PDF or HTML)
• prepared Foam Board Model
• 16 oz. granulated sugar
• 5 lb. flour
• 8 oz. mashed potato flakes
• protractor
• newspaper

1. An integral part of avalanche research is understanding the complexities of snowpack formation and using this data to make predictions about how particular slopes might behave. In this activity, students layer foodstuffs to mimic the strong and weak layers within a snowpack and then cause an avalanche to occur.

2. Prior to the activity, you will need to construct boards for each team using the "Foam Board Model" directions.

3. Once the models are made, divide students into teams, gather materials, and distribute the "Slip Sliding Away" student handouts.

4. In Part I, have students predict how the snowpack will behave at different inclines on each surface. Then have students layer sugar, flour, and potato flakes to simulate different layers in a snowpack over winter.

5. In Part II, students begin to incline the board and record data as their snowpack begins to slide.

6. Conclude with a class discussion about how slope, terrain, and different layers within the snowpack affect its stability, and how objects on slopes both help prevent avalanches from forming as well as become areas of stress for triggering them.

The word avalanche is derived from the Latin word meaning to "slip, glide down, and flow." Although almost anything that slides down a mountain or hillside (mud, ice, or rocks) can be called an avalanche, the term most commonly refers to snow slides.

A snowpack accumulates by layers with each new snowfall or drifting of snow. Layers within a snowpack vary and constantly change mainly due to temperature changes in the air and within the snowpack. Some layers are weak with limited bonding between snow crystals, while other layers are strong with well-bonded snow crystals. In this model, the sugar represents a weak layer at the base of the snowpack. The flour represents a strong layer, and the potato flakes simulate a second weak layer between the flour layers. The surfaces on the foam board represent various ground surfaces under the snowpack.

As the incline of the board is increased, the stress on the snowpack increases. In nature, avalanches can occur on slopes with angles above 25 degrees but are most common on slopes of 35 to 40 degrees. Students should expect to see slides on the smooth acetate surface at a lower incline angle. This is because there is very little to anchor the snowpack to the hill or mountainside. The top flour layer will likely slide first along the weak layer of potato flakes, and as stress builds, the entire snowpack will slide.

A strong layer does not necessarily mean it's a stable layer. Slab avalanches occur when a relatively strong layer lies on top of a weak layer. In a slab avalanche, the snow breaks off in a single plate, which then fractures and slides down the slope. Students are likely to notice a slab avalanche on the burlap surface, which anchors the weak sugar layer. As a result, only the top flour layer breaks off and slides when the underlying weak potato flake layer fails.

The rocks on the plain foam and the burlap surfaces represent trees or rocks on a mountainside. Rocks and trees will help anchor a snowpack, but they are also areas of stress concentration which can trigger avalanches. If anchors are completely buried under snow, their ability to hold the snow decreases.

This model simulates only a few of the variables that scientists consider when predicting avalanches. Avalanche forecasting can be compared to the more familiar task of weather forecasting. Predicting avalanches, however, is more complex than predicting weather because it includes all of the variables associated with weather along with other variables such as snow type, terrain, slope, and chance events.