Wednesday, March 16, 2011

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European scale avalanches. Interpreting the Portalet

European scale avalanches. Interpretation

European Scale avalanche is currently 5 degrees, ranging from weak (1) to Very Strong (5).

Although the criteria to assign each risk level are written in the scale and should be standard across Europe, there is often disparity between the bulletins read before leaving the mountain. We usually refer to the Pyrenees Meteo France, the Catalan IGC and AEMET . Everyone has their own way of working and developing newsletters.

At the same time, personally attempt to develop a newsletter for the Pyrenees snow basing on data I get from shelters, Internet, weather prediction models, calls to climbers who are on the mountain and through my own experience , if it so happens that I come from being in the mountains.
try to offer a gradation of risk in line with European standards, striving to be rigorous, without pulling upward, so that each level of risk to maintain the attention it deserves.

In line with this, the other day Astún met in one of the guides Jaca, with whom I was talking about it. He has sent me a statistic made in the Aran valley on the percentage of accidents due to the risk avalanches had in recent years. Apparently, the 79% of avalanche accidents were with substantial risk (3) , 14% with Strong Risk (4) and 7% Limited Risk (2).

With this, we can see that the vast majority of accidents occur nuetra Pyrenees with significant risk (3). Personally I think this is because they do not really know the meaning of Risk 3. When we read all too frequently giving Risk 4, as usual frequency should not exceed 1 or 2 days a month, stop scare Risk 3. And we, we try to give more or less stringent newsletters, is when we begin to frighten us.

Next story explaining the European scale avalanches, from the book "Avalanche 3x3" Werner Munter . In this book teaches a method with which, from a strictly local avalanche bulletin, we know what kind of earrings as we tackle the risk is 2, 3 or 4. In
input to carry out his method, you need a reliable newsletter, rigorous, conforming to reality and which does not tend to swell, to rise, the actual risk. For if the risk is fatter "upward" to cover health, that is when the Risk 3 is no longer considered the most dangerous of all.

is interesting to read the lines below and see how often the risks that occur in a normal season in the Swiss Alps. Here goes:

By Werner Munter

CONCESSIONAL usually takes 1 / 3 of the season
The snowy mantle is usually seated.
may trigger spontaneous avalanches will be minor, especially if the snow is wet.
Landslides triggered by skiers plate can only occur with significant overloads on steep slopes, especially near ridges and have been newly created vent deposits in high mountain snow.

usually takes 1 / 3 of the season

Some locations, directions and altitudes part described by the avalanche, the snowy mantle is only partially stabilized. These specific areas require carefully chosen route.
Skiers can trigger landslides in the event of overloads important (several skiers together.)
In the steep, snowy mantle which is particularly bad, we can not exclude the detachment caused by a single skier. On slopes of this kind can also occur spontaneously isolated landslides, which often increase as they get down (with some exceptions in the spring).

Dura 1 / 4 of the season
In many places, altitudes in situations and described by the avalanche part, the snowy mantle is moderately or poorly stabilized. isolated Skiers can trigger avalanches on these slopes described.
spontaneous avalanches are common on steep slopes. They can acquire considerable size in some cases and cover areas with little slope. Unchainings may also occur remotely from the base of the slopes.
Sound "Boum" to repeat characterizes the degree of risk . But overlap there is another threat that does not advertise its presence by signs.
excursions in the mountains on skis requires experience and sufficient knowledge of snow and avalanches to be able to choose an optimal route using all the advantages of the field.
When crossing a slope to another, the path of descent should not be steeper than the ascent. It is prudent to continue lowering the footprint and give rise to variants of steepest descent, even if they are shorter.

strong risk (4): HIGH RISK
Usually only lasts a few days a year.
(According to Jimmy Oden, + or -1 day a month, maybe 2).
The snowy mantle is weakly stabilized and steep slopes (> 30 º) are dangerous in all orientations. The
spontaneous avalanches may acquire large proportions and cover areas that were reputed to be safe at Risk 3, to extend for large areas of flat land.
remote triggers, even at great distances, are characteristic or even typical of this level of risk.
can no longer speak of calculated risk, so that we can only move moderately sloping terrain on the can access without diagonals (<30º).

is exceptional.
(As Jimmy Oden, 1 day per season)
avalanches reach the plain. It is recommended not to leave shelters or any other room and wait.
irrigation decreases very quickly in general.
Ni forest roads surrounded by protective trees can be considered a safe place.
Werner Munter

Well, do you think ?
Have you noticed the number of days per season usually there each risks described?

official scale I hope this makes us more knowledgeable about what it means Risk 3 when we see it in bulletins. ( At least, in the newsletters I personally try to send each week, with more or less correctly).
You know nivológicos bulletins are only estimates made from limited data and information (cut by snow guards shelters, special observers, global weather forecasts) and also are regional, not local (Except that developed for the Aran Valley .) Unable to focus in every valley and every particular area, which in a general Risk 3 for the Pyrenees, we risk zones 2 and a few specific areas of Risk 4, if in this particular valley, the wind blew and it snowed more more than others.
nivológicos Newsletters are of general assistance to begin to estimate at home, as we inform the media, how's the mountain and how will qeu behave in the next 24-48 hours. From there, we will develop an initial plan for the weekend and, if anything, a plan B in reserve. Since then the mountain, each group shall be based on assessing the situation observation of the terrain, the mountain of information is giving us every minute and based on personal experience. So try to predict the potential danger or safety of the slopes to cross.
I hope these lines will be of assistance. Good snow at all. Jorge García-


PS: What are steep slopes?

steep slopes usually consider when they have more than 30 º. Very steep if you go from 40 º.
But of course, is not easy to calculate the slope of a hillside "A view." There are several methods, some more complex than others. I commented one of them.
simplifying a bit, we can use two ski poles to try to estimate the steepness of the slope. If we place a vertical dive to the rosette and the other horizontally to touch the snow with the handle (the latter having the rosette of horizontal cane stick touching the vertical axis) we can estimate the inclination is shallow.
The equation for calculating the angle alpha is complex to explain in few lines, but can be simplified as follows. If the horizontal pole that touches the top of the slope less than half the height of the cane vertical, the inclination of the slope is usually about 27 degrees about .
That is, if the horizontal pole does not exceed half the vertical stick, we will be moving on relatively safe ground. If the union of the poles above crosses half the vertical stick, we are approaching a slope greater than 30 and therefore becoming less stable. From there, calculate if the slope is 30 or 35 or 40 degrees possible only having scored the staff (at home) calculating length of the rods and angle alpha, which is more complex (and I know it. But July Beneden, having his staff or "palómetro" marked with the cm of snow depth and the degree of tilt as the height of the vertical pole).
Anyway, for people in general, knowing that the midpoint of the stick would be about 27 degrees, enough to have marked that half of the stick with tape or marking pen, to get an idea of \u200b\u200bthe steepness of the slope on which we operate.
Finally, it is a very simplified and not entirely accurate, but we can give a little more information quickly and easily when assessing the risk from one side to cross over and help us assess whether or not avalanche adopt a protocol: separation of skiers, looking for another path softer, etc. Jorge


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