6.1.12 Shear quality
Shear quality is the resistance of the layers in a snowpack when an amount of pressure is applied to one layer, such as the top, and the rest are left alone.
Shear quality is measured by exerting increasing amounts of vertical pressure on the top of the snowpack until the top layer begins to move down the slope. There are several types of shear quality tests.
The Rutschblock test is a rather crude, time-consuming technique done on-site by a snowpack expert on skis. First, the skier digs a u-shaped trench around an undisturbed block of snow, leaving the block attached on the uphill side. Then he or she performs a series of increasingly stressful maneuvers to see if the block will fail at any weak layers and begin to move. These range from gently stepping on the block to jumping up and down on it. The point at which the block moves is recorded.
The Stuffblock test is a variation on the Rutschblock test. It is more quantifiable in that pre-set amounts of weight are exerted on a column to see when it will fail.
To do the test, you fill a stuff sack with ten pounds of snow and drop it from increasingly greater heights onto a shovel blade on top of a column of snow, noting the point at which the column fails. The test can be done by skiers and non-skiers alike, which is an advantage in some situations.