How dangerous is the snowpack? You now know the basics regarding probability the likelihood of triggering. So, just because you can easily trigger an avalanche does not necessarily mean the hazard level high. If the avalanche is very small and very soft, it’s usually not a dangerous avalanche—low hazard. On the other end of the spectrum, if you could trigger a huge, unsurvivable avalanche, but there’s a very low probability of doing so, it’s also low hazard. Thus, hazard is always a combination of probability and consequences.
How dangerous is the snowpack?
Consequences are what will happen if it slides. This section covers only avalanche hazard; people and terrain are introduced to the risk equation later. With avalanche hazard, consequences refers only to the relative danger of an avalanche, which depends not only on the mass of the avalanche but also on its hardness and density. Here, you’re in luck, because for many years, avalanche professionals have been ranking avalanches by their destructive size, which factors in the mass of the avalanche plus destruction an avalanche causes on a one-to-five scale
If you know the likelihood of an avalanche and the expected size of an avalanche, you can plot it on what risk managers call a probability-consequence diagram. If you search for this term online, you will see similar graphics from a wide variety of fields that deal with hazard. In the avalanche world, the vertical (probability) axis is called likelihood and the horizontal (consequence) axis is the aforementioned destructive size.
Several different kinds of avalanches on the hazard scale
Which is a convenient way to think about the probability consequence tradeoffs with each kind of avalanche. For instance, shallow storm slabs are often high probability low consequence, meaning that they may be fairly widespread, but being soft and shallow, they are easier to trigger with slope cuts. More conventional avalanches fall in the middle of the diagram, because they are harder to trigger and large enough to injure or kill people.
Avalanches that occur during very large storms usually plot in the upper right corner, because they occur naturally (high likelihood of avalanches) and are very large. Then, there are the very tricky avalanches that account for most avalanche fatalities the low-probability, high consequence avalanches difficult for a person to trigger, but if you do, they are very large and unsurvivable. Inexperienced or avalanche-unaware people often fall prey to them because they can have other tracks on them, making them look safe, then someone finally finds the trigger point and brings the whole mountainside down. Yikes!
The final factor in this assessment process is uncertainty, which is a central part of any discussion or calculation of hazard or risk. What we don’t know is often more important than what we do know. Uncertainty is a major driver of stock markets, politics, business, and world events—and so it is with avalanches.
Thus, it’s important to have a way to graphically account for uncertainty on the hazard diagram. You never know the exact likelihood of triggering or the size of the avalanches to expect on a given day, but you can often express a range of possibilities. Uncertainty can also come from lack of information or poor-quality information. In either case, both variability and uncertainty can be indicated on the diagram by the size and shape of the ellipse drawn.
It is an example a forecaster can graphically likelihood, size and variability/uncertainty on one diagram so that, at a glance, other forecasters or the general public can instantly visualize the avalanche problem types for the day. Avalanche geeks like me get really excited about tools like this. Any graphic or system that can organize complex information is a wonderful thing.