Avalanche problems and danger patterns have one thing in common: They point out typical, repeating and most often obvious dangerous situations.
The difference is at which level we look at it. Avalanche problems give a first, rough overview of sources of danger (e.g. new snow) whereas avalanche danger patterns give deepening background knowledge about the cause of the problem (e.g. problem due to extra load on a weak layer). Danger patterns therefore describe possible scenarios resp. processes that lead to avalanche problems.
The objective is clear: With the help of avalanche problems and danger patterns, dangerous situations can be identified faster, the behaviour can be adapted and avalanche accidents prevented.
Avalanche problem - new snow
Travel advices: Be patient and check for critical new snow amount and recent avalanche activity!
The avalanche problem is determined by current or most recent snowfall. Important is the critical amount of new snow which depends on different factors.
If new snow is not influenced by wind and lies on a solid snow pack loose snow avalanches can be observed in extremely steep terrain. Very intense snowfall can lead to very large avalanches triggered by the weight of the snow pack leading to the failure of weak layers near the ground. Snowfall typically arises together with wind resulting in a combination of the avalanche problems new snow and wind-drifted snow. Specific conditions regarding new snow are described in dp.4 (cold following warm / warm following cold) and dp.9 (graupel blanketed with snow).
The avalanche problem new snow is fairly easy to recognize. Check for critical new snow amount and recent avalanche activity.
Possible danger patterns are dp.1 / dp.4 / dp.5 / dp.8 / dp.9
Avalanche problem - wind-drifted snow
Travel advices: Consider wind signs and locate wind deposits!
The avalanche problem is determined by wind-drifted snow. Snow can be deposited with (combined new snow and wind-drifted snow problem) or without a snowfall.
Weak layers within the snow pack are the key to understand this avalanche problem. Wind slab is deposited on top of these weak layers. Important is the type of crystals the weak layer is made of, which influences the life time of the weak layer. Very durable are faceted crystals, depth hoar as well as surface hoar.
A newly constructed weak layer within the new snow is also very common. If during a cold period powdery snow is covered by snowdrift this weak layer forms and slab avalanches can be triggered very easily due to this weak layer.
If not hidden by new snow layers the wind-drifted snow problem is usually easy to recognize with training and good visibility. Insider wind signs and locate wind deposits. Typical clues: snowdrift deposits, shooting cracks, sometimes whumps and recent drifting snow avalanche activity.
Possible danger patterns are dp.1 / dp.4 / dp.5 / dp.6 / dp.8
Avalanche problem - old snow
Travel advices: Choose a conservative behaviour and take extra caution in snow-poor zones and transitions from snow-poor to snow-rich zones!
The avalanche problem is determined by the possible presence of critical layers in the old snowpack. Snow layers are defined as old when they have not been modified for several days by precipitation, wind or melt processes.
In snow-poor regions or winters the avalanche problem old snow occurs more often than in snow-rich regions or winters. All expositions are affected, but mainly shady slopes. In snow-poor regions or in areas with transition from snow-rich to snow-poor primarily slab avalanches can be released by additional loading. Even in flat areas avalanches can be triggered. Fractures can propagated over long distances – and therefore trigger big avalanches. The avalanche problem old snow is hard to assess and persistent, which can be seen in the statistics: If well-educated persons die in avalanches, this happens mainly due to an old-snow problem.
In these situations conservative behavior is needed and – for experienced persons – investigations of the snow pack are helpful. If a significant weak layer exists at top of the old snow, a new snow problem becomes an old snow problem after a few days without precipitation. A combined old snow / wet snow problem can be found during the drenching of the snow pack in spring. Background knowledge about the old snow problem can be found in dp.1 (deep persistent weak layer), dp.4 (cold following warm / warm following cold), dp.5 (snowfall after a long period of cold), dp.7 (snow-poor zones in snow-rich surrounding) and dp.8 (surface hoar blanketed with snow).
Possible danger patterns are dp.1 /dp.4 / dp.5 / dp.7 / dp.8
Avalanche problem - wet snow
Travel advices: Good timing and trip planning are important!
The avalanche problem is determined by weakening of the snowpack due to liquid water. This can be caused by high temperatures, warm winds, strong solar radiation, rain on snow or a combination of these factors. Particularly critical are the first wetting period, massive backwater on a solid crust or the transition between snowfall and rain.
Wet snow avalanches have a high destructive potential, regardless of whether they are slab, loose snow or gliding avalanches.
Wet snow problems are fairly obvious. Good planning and timing are very important, because the danger increases with the wetting of the snow pack. Background knowledge about wet snow can be found in dp.3 (rain) and dp.10 (springtime scenario).
Possible danger patterns are dp.3 / dp.10
Avalanche problem - gliding snow
Travel advices: Avoid areas around glide cracks!
This avalanche problem is characterized by the gliding of the whole snow pack on steep, slippery surfaces. Often the formation of cracks in the snow pack serves as a warning sign. The release of a gliding avalanche cannot be predicted! Nevertheless they occur mainly in autumn after heavy snow falls or in spring during the first drenching of the snow pack.
Possible danger pattern is dp.2