There are two types of defense structures built to help control avalanche
flow,
1) defense structures which retard, divert or halt the motion of
moving snow and
2) control structures which alter the deposition of snow to
help in eliminting the possibilty of an avalanche occurring.
To determine what type of structure is needed for the avalanche area in question it is neccessary to understand the properties of snow and the expected type of avalanche. The two types of avalanches focused on are loose snow and slab. Each of these types of avalanches has a wet and dry component. Loose snow avalanches are the least threat to human life because they move slow, include very little snow and are easy to predict therefore control structures are used for this type of avalanche. Slab avalanches pose a significant hazard because they have a large mass, move rapidly, and are difficult to predict. Defense structures are used to control these types of avalanches and in some cases control structures are added near the initiation area to help in altering the amount of snow accumulation. If the slab avalanche is wet it will move at a faster rate than the dry slab and requires a more sophisticated defense structure, such as a straight wedge, which can seperate the mass into two different flows and help to elivate the impact.