Fókablog

Lavinaskála

2009. október 30. - viktor.agoston

 

AVALANCHE DANGER LEVELS according to TOPR
AVALANCHE DANGER LEVEL
SNOW STABILITY
AVALANCHE PROBABILITY AND TRIGGER
RECOMMEND ACTION
1
LOW
GENERALLY SAFE
Generally stable snow
Possible small avalanches in the form of slides, particularly with wet snow. 
-----------------------
Avalanches may be triggered on few extremely steep slopes with the angle equal to or greater than 40°, exclusively with very large additional load **.
Mountain wandering is generally safe. Very steep and extremely steep slopes with angle equal to or greater than 40°, and particularly couloirs, depressions and vast snow fields, particularly near the ridge, should be traversed (skied) one by one. Avoid any areas with wind accumulated snow (so called snow beds), and specifically on extremely steep slopes with angle equal to or greater than 40°, in couloirs, depressions and vast snow fields.
2
MODERATE
DANGEROUS CONDITIONS
Generally moderately stable snow, but on certain steeper terrain at 35-40° angle, and particularly on extremely steep slopes where the inclination is equal to or greater than 40°, may be rather unstable. 

Possible self-triggered, single, small avalanches. 
-----------------------
Avalanches may be triggered mostly on extremely steep sloes of 35-40° angle, by large additional load **. On some, extremely steep slopes with the angle equal to or greater than 40° of unfavourable orientation*, medium sized avalanches may be triggered already by small additional load** .
Partly unfavourable conditions for wandering in the mountains. Recommended to refrain from going across or under any slopes having the angle equal to or greater than 40° particularly on the lee side and unfavourable orientation*, and any shaded formations near ridges. Beware of deposits of windblown snow on hard interface. On steep, 30-35° angle slopes and very steep, 35-40° angle slopes please move with caution and one by one, keeping safe distances (at least 10m). Avoid any couloirs, depressions and vast snow fields. Safe travel requires the ability of independent evaluation of avalanche danger in the field and cautious selection of the path.
3 
MODERATE TO HIGH
CRITICAL CONDITIONS!
Conditions generally unfavourable. On many steep, 35-40° angle slopes the snow stability is, at the most, moderate, or poor


Possible frequent, self-released medium sized or single large avalanches, sometimes even reaching valley ground.
-----------------------
Avalanche trigger is possible mostly on steep, 30-35° angle slopes already by small additional load**. On certain extremely steep slopes of 35-40° angle, medium sized avalanches may be triggered from great distance already 
by small additional load**. 
Conditions rather unfavourable. It is recommended to refrain from going across or under any slopes of 35° or greater angle. On 30-35° angle slopes move with caution and one by one, keeping safe, large distances (at least 15 - 20 m). Absolutely avoid any couloirs, depressions and vast snow fields.
Safe travel requires high experience and expertise in independent evaluation of avalanche danger in the field. It is recommended that the less experienced go to the mountains with a professional guide only or refrain from travel in mountain areas over the top natural tree line. 
4 
HIGH
EXTREMELY CRITICAL CONDITIONS!
Unfavourable conditions. Snow highly volatile on all steep, 30-35° angle slopes. 


Possible self-released large avalanches threatening usually safe areas, often reaching the counter slopes. 
-----------------------
Avalanche trigger very probable already on moderately steep slopes with the angle equal to or greater than 30° by small additional load** from a very big distance. .
Conditions clearly unfavourable.
It is recommended to refrain from any trips in mountain terrain and to refrain from travel in the lower situated areas - under and across slopes with the angle equal to or greater than 30°.
5 
EXTREME
CATASTROPHIC CONDITIONS!
Unstable slabs on majority of terrain, snow cover highly volatile

Many large self-release avalanches should be expected, including on relatively low angle terrain with the inclination equal to or greater than 30°. The threat applies to entire valleys, including their outlets.
Travel in the mountains is generally impossible.
 
REFERENCES:
*CAUTION!!! as particularly dangerous one should always consider the north-east, north and north-west oriented slopes. The factors which radically increase avalanche danger are strong wind combined with snowfall; the direction of the wind and location of snow deposits in the field should be closely observed. 
** additional load: 
-very large - e.g. a large group of foot passengers (e.g. 4 and more persons) or a group of dynamic skiers or snowboarders (particularly their falls), not keeping proper discharge distances.
-large - e.g. small group of tourists (e.g. 2 - 4 persons) going up on skis without distances, or a falling skier, also one foot passenger.
-small - e.g. one tourist going up on skis, or one skier skiing smooth curves, not falling

*** slope angle:
-moderately steep 30° 
-steep 30-35°
-very steep 35-40°
-extremely steep 40°
MOUNTAIN TERRAIN - means the mountain terrain located above the top of the natural tree line .
 
Avalanche size (international definitions)- approximate data:
Avalanche size
Runout Classification
Damage potential classification
Quantitative classification
1
slide
snow relocation without danger of burying (danger of falling)
are relatively harmless to people
avalanche
path < 50 m
mass < 100 m3
2
small
stops within slope
could bury, injure or kill a person
avalanche
path < 100 m
mass < 1000 m3
3
medium
reaches end of slope
could bury and destroy a car, damage a truck, destroy a small building, or break a few trees
avalanche 
path < 1000 m 
mass < 10000 m3
4
large
reaches valley ground, and even the counter slope
could bury and destroy a railway car, large truck, several buildings or a forest area
avalanche
path > 1000 m
mass > 10000 m3
 

 

 Hasznos források:

 www.slf.ch/english_EN

www.topr.pl/html/opis_stopni_zagrozenia_lawinowego_ang.html