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ATES (Avalanche Terrain Exposure Scale)
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ArticleId: 3639 Written: 2010.12.30 by: Frank W. Baumann

Is anyone using it? Do you think it works to improve avalanche safety?

The Diamond Head area near Squamish is considered "Simple" terrain- which means that no special precautions are needed as long as the avalanche danger is "Considerable" or less. Right now, however, there are some troublesome persistent weak layers in the snowpack- which means that numerous specific slopes in the Diamond Head area could generate human-triggered avalanches large enough to kill someone.

A cubic metre of dense snow typically weighs about 350 kilograms, which means that it only takes three cubic metres of snow resting on a moderately-steep (30-40) slope to produce a sliding mass of snow weighing more than one metric tonne. A Size 2 avalanche- defined in Canada as one that could bury, injure, or kill a person- typically has a mass of 100 tonnes- which translates into approximately 300 cubic metres of snow, or, for example, a slope that is only 20 metres long, 15 metres wide, and is covered with a metre of unstable snow.

Given how little snow it takes to produce a dangerous avalanche, this then begs the question if it is ever possible to realistically classify any mountainous terrain into three simple categories, and thereby provide a reasonably safe method for winter recreationists to assess the terrain they are going through? If not, then the ATES system is giving winter recreationists a dangerous false sense of security with regard to managing avalanche risk. The recent death of a snowmobiler in the Coquihalla Lakes area near Hope, B.C. may be a case in point: the avalanche danger was rated as "Considerable", he was sledding in overall "Simple" terrain- but was still killed by an avalanche.

My suggestion: use the avalanche danger rating, the slope angle, and the volume of snow that could release as prime factors in deciding whether a given slope could potentially avalanche or not. Specifically, consider yourself exposed to avalanche risk if the avalanche danger rating is more than "Moderate", a slope is steeper than 25, and that slope could have more than 100 cubic metres of unstable snow.


Comments

#1505 - 2011.01.05 Frank W. Baumann - Definitely a wet snow slush avalanche
Nope. Definitely a wet snow slush avalanche. I was with a Blackcomb pro patroller and several other very experienced avalanche types and we were all just boggled. Again, for years, I did have pictures- but they were 35 mm slides which are buried somewhere in the thousands of other photos I have from the pre-digital era.

A similar event came down Shannon Falls one year after a freezing spell that was followed by heavy rain and warm temperatures. It was more of an ice avalanche- but it flowed down almost to the parking lot.

With regard to avalanche hazards along the marked winter route- I'm not familiar with the site you noted (49.770214, -123.000477), but am aware of another place near 49.76434, -123.02281 where the marked wands cross the top of a 34 slope that could potentially avalanche- that is, the route did cross the top of a viable starting zone. Again, this area is discussed in this reference article here on Bivouac- which includes a picture of the site. I haven't checked the wanded winter route this year- but it would be very easy to move the wanded route up only a few metres and be above the starting zone in totally safe terrain.

Up until a few years ago, the wanded route followed the summer road through Red Heather Meadows. But at one point, the road crosses right underneath a more serious avalanche slope at 49.759856,-123.034275. Fortunately now, the wanded route has been moved to a safer area on the north side of Red Heather meadows.

BTW- I like using decimal degrees (NAD 84 datum) for locations- makes it easier to copy and paste into Google Earth.

#1504 - 2011.01.05 Steve Grant - Falls Avalanche, Slope that Concerns Me (Photos)
Frank, I don't want to be argumentative, but the Brandvold Falls "slide" may have been more of a creek overflow event than an avalanche.

I've skied down the falls now and then since the '70's, and it consists of a series of snow pillows rather than a continuous slope. A greater danger is getting sucked in between the pillows or into the stream itself. It's not a very good ski run, but is excellent entertainment.

The coordinates for the slope that more concerns me on the Diamond Head winter route is at N 49:46'12.7" W 123:00'1.8". On occasion I have skied across the top of it rather than cut across the middle on the wanded route. I'll try to insert a photo, taken today, of the slope. Hmm, can't find a way to do this. So what else is new?

#1503 - 2011.01.04 Wilf LeBlanc - brandvold falls
I think the falls do fall into the acceptable risk category at any time of year. But I still wouldn't sit under them and have lunch on a warm spring day either.

Most people either don't seem to know when they are at risk, or understand that when you're at risk it really makes sense to limit the time exposure (move past the hazard quickly). And more than a few people (judging from the tracks we all see) take unnecessary risks such as traversing under steep slopes when a safer alternative 50 feet away is available.

#1502 - 2011.01.04 Scott Nelson - Normal Caution
The CAC Avaluator trip planner tool recommends "normal caution" when traveling in simple avalanche terrain at a considerable rating. "Normal Caution" is not the same as "No Caution". To me, "normal caution" means carrying avalanche rescue equipment, good route selection and group management practices.

#1501 - 2010.12.31 Frank W. Baumann - Brandvold Falls
Believe it or not, it has avalanched- during one warm and rainy period in early 1979, the whole waterfall area flushed out and spread a wet snow slush avalanche directly down the trail to the big trees that are right beside the trail about 20 metres from the waterfall.

I do have pictures of the event- but it would take too much time to find them.

An important exercise to complete when you're touring is to recognize the point at which you cross from absolutely no avalanche hazard, to some potential hazard. Rarely would Brandvold Falls mark that point- but lots of ski tourers miss the obvious point on the summer trail below High Point where in fact serious avalanches can and do occur. This area is discussed in this reference article here on Bivouac.

#1500 - 2010.12.31 Steve Grant - Complexity
People seem to be looking for reassurance of their fears for their safety in the winter backcountry. It's easy to meet that market with courses and techniques that necessarily simplify the situation. People aren't anxious to hear that the winter backcountry is infinitely complex, that no equipment or training can come close to containing that complexity and so their survival depends greatly on their wits. They aren't going to pay to be told that.

I notice that BC Parks avalanche advice for the standard winter route to Diamond Head mentions Brandvold Falls as a potential avalanche site. I've been going there since the lodge was still open, and I've never seen the falls avalanche. On the other hand, on the marked winter route there are some very steep forested sidehills, and one open slope with a bad runout with the marked winter route across the very middle of it. It's steep enough that if you're traveling northbound using wax, you can get a few turns in on it. These spots don't ever seem to be cited as hazards.