Avalanche

22 Mar 2017 19:13 - 22 Mar 2017 19:14 #71194 by intrepid
Avalanche was created by intrepid
Not an every day topic in SA, and thankfully something we probably never need to worry about in the Berg. Nonetheless, avalanches are a fact of life elsewhere in the world and a very important consideration in some mountains. In British Columbia, Canada, there have been 4 avalanche fatalities in 2017 so far. Here we have something called an avalanche forecast, which is as important as the weather forecast and often determines how a trip into the mountains is planned, and if it even goes ahead or not. They can occur at any time of year in the Canadian mountains, but are mostly an issue from about December through to May. As the spring warming slowly moves in, the size of the avalanches can get quite big. There have been size 3's reported in BC recently, including my neck of the woods (the size scale is from 1 to 5, a size 3 is over 1000 tons of snow and can destroy houses and trees).

This particular GoPro video went viral around here when it happened about 2 months ago. The guy was wearing an avalanche airbag in his pack which evidently played a large part in his survival:


An update published yesterday from one of the ski areas in BC, some impressive footage between minutes 1 and 2:
vimeo.com/209321060

A video of a controlled avalanche recorded last year, triggered by explosives. They do this to protect roads and ski resorts. Gives a good picture of what BC looks like at this time of year:

Take nothing but litter, leave nothing but a cleaner Drakensberg.
Last edit: 22 Mar 2017 19:14 by intrepid.
The following user(s) said Thank You: ghaznavid, Captain, Richard Hunt, saros, timoross

Please Log in or Create an account to join the conversation.

More
30 Mar 2017 11:57 #71209 by Deanvdm
Replied by Deanvdm on topic Avalanche
Just about all Souf-effircans (me included) have no real snow experience to hold any authoritative opinion about snow so take what I say with a pinch of salt.

I agree with you statement that we probably almost never would have to worry about avalanches in the ‘Berg but avalanches, or at least smaller releases, do occur every now and again in the ‘Berg and if you know what to look for you can see some evidence in steep gullies after very big snow dumps (every couple of years). However as you know and hint at there are avalanches and there are avalanches and the type of avalanche you see one of your videos and which often make news headlines abroad are wind slab avalanches triggered by humans after building up in very specific conditions on certain slopes. In SA we typically do not get enough layers of snow under the “right” conditions to create such avalanches as the snow melts and seldom builds up a base layer let alone create weak layers for additional top layers to consolidate and slide on the weaker layers ect. We’re lucky to get one big dump, let alone several dumps of snow to build up.

But there other types of avalanches and they are characterised by the snow conditions which forms them and how they are triggered.

One type which has been recorded in the ‘Berg is a loose snow avalanche (aka a sluff). This is the type of avalanche which happens (among other circumstances) during or directly after a significant snow storm on steep slopes (typically steeper than the wind-slab prone slopes) and often in windless circumstances where the accumulated powered snow builds up to such a level that it can triggers by itself or from a piece of ice or rock falling on it and then the loose snow slide down as there is nothing to hold it on to the rock and earth below. In most cases there is a natural limit to this kind of avalanche as there is only so much powder that can accumulate on steep slopes and gullies before it self-triggers (wind slab can build over many storms and get really big before it is triggered) but at the extreme end of the spectrum you get a powder avalanche which can be one of the most destructive forces in the mountains and have in the past covered whole building/towns (which is one of the reasons why you have, as in your video, avalanche teams in the ski areas using explosives to trigger potentially prone slopes before it builds into something that can risk lives in the village below).

I’m sure you have read the excellent book “Dragon’s Wrath” by James Byrom and Reg Pearce about accidents in the berg which and the excellent work that the MCSA KZN Search and Rescue team and the SA Air Force has done in the ‘Berg. The chapter on the “Big Freeze of ‘88” has an account of an exceptional snow blizzard which trapped several groups of hikers. The “Harrison” group was one of them and there is a gripping, film-worthy account of the party being pummeled by multiple loose snow avalanches (including some of the group being buried in it). Their ordeal includes close shaves, a slide on ice to the edge of a cliff, loosing shoes, blackened frostbitten toes, some serious exposure and also excellent character and leadership which got the group though (but take note that they made some very bad decisions about gear etc. when they started the hike). The group managed to descend from the snowed-over escarpment down a gulley / pass and in doing so got themselves in the way of several avalanches. Along the way they managed to find some unknown caves to shelter in (but also nearly got trapped in one via an avalanche). The actual “pass” that the group descended is not any of the “hiking” passes and they were only able to do so due to the significantly built-up snow which allowed them to jump off little cliffs into the deep snow drifts below – in fact the helicopters searching for them did not spend much time searching that gulley as it was not thought possible for the group to consider / descend it.

Personally, I've only seen a couple of avalanches (the place where it is guaranteed for plebs like me is on the Cordillera Huayhuash trek in Peru in early season where the back of Siula Grande and the neighboring peaks from Touching the Void fame has frequent icefall style avalanches) but the only thing that I saw in the ‘Berg that comes vaguely close to an “avalanche” was a small release of a couple of cubic meters of snow when things started to warm up and slide (a different set of conditions again) but that can hardly be called an avalanche in the normal sense of the word. I think it is unlikely that any of us will ever be in any real danger from an avalanche in the ‘Berg. But (crossing fingers) perhaps we get a good dump or two this season to allow us to experience the magic of a ‘Berg hike in true winter conditions (assuming you have the right experience and gear). The ice climbers among us are very hungry for some good ice though – the past couple of seasons has been thin and uninspiring to say the least.
The following user(s) said Thank You: intrepid, JonWells, Andreas

Please Log in or Create an account to join the conversation.

More
30 Mar 2017 18:58 - 30 Mar 2017 19:09 #71215 by intrepid
Replied by intrepid on topic Avalanche
Thanks Dean, certainly a valid point that the Berg isn't totally risk-free in this regard. I have the first edition Dragon's Wrath which doesn't have that account in it. Surprising to hear that some actually got buried, but good to know. I will try get hold of a later edition. I guess most of us only wish to get the timing right to see that much snow in the Berg (a desire I have been cured of since living in BC! :laugh: ). And its very true that even very small avalanches or even sluffs can cause problems if there are so called "terrain traps" - they can push you over a cliff, slam you into rocks, and even bury you in a trench or gully.

Here the persistent slab avalanche type is one which can be very big and destructive (can cause size 3 and up). On top of that it is tricky to manage and the risk can linger for weeks on end. They also have numerous trigger mechanisms. They develop when a crust is formed, which doesn't bond well to fresh snow on top it, and then gets buried deeply. It may remain unreactive for some time and then suddenly become reactive through spring warming, for example. We have a maritime snowpack where I live, which is several meters thick and we easily get these weak layers deep down. In our local avalanche forecast there has been a lot of talk of one such persistent weakness. It was formed in mid February through a melt-freeze cycle, with a layer of surface hoar (frost on snow) on top of it. This layer now lies at 150-200cm in the snowpack. The latest report indicated that this layer is starting to become dormant, thankfully. On top of that we have a rain crust from mid March, which is 20cm thick and buried at 100cm, and then another melt-freeze crust from a week ago, which is buried at 60cm. Hopefully the spring warming will settle these crusts quickly!

Take nothing but litter, leave nothing but a cleaner Drakensberg.
Last edit: 30 Mar 2017 19:09 by intrepid.

Please Log in or Create an account to join the conversation.

More
05 Apr 2017 19:10 #71274 by intrepid
Replied by intrepid on topic Avalanche
Some avalanche types...

This must have been a pretty large slab avalanche, judging by the length and depth of the crown (the obvious line where the avalanche broke away). Seems it happened some time before this picture was taken judging by the lack of avalanche debris, the slopes having been smoothed over. The balls of snow rolling down the slope (called "pinwheeling") is as a result of solar heating of the snow surface.


This slope has two observable crowns from slab avalanches. The one to the left below the ridge line is obvious, and a second one can be seen if you look closely on the big slopes along a straight line directly down from the summit. This may even have been from two separate avalanches. In addition, on the left hand ridge on the summit cone is what is probably a glide crack which can eventually lead to a glide avalanche (when the entire snowpack slowly glides slowly downwards and eventually breaks away).


This next one is on the same mountain as above, but on a different aspect, and shows 2 different types of avalanches. The one on the left is due to solar heating on the rocks, which eventually warms up rock lying under the snow causing it to melt the snow. On the right is an avalanche track from cornice-collapse. The cornice is the distinct wave-like feature on the ridge line to the right. Both of these avalanches were small and these types are typical spring and early summer issues. While these two avalanches wouldn't have easily bury a person on this terrain, the big chunks of cornice lying in the avalanche track would cause problems if it hit you.


This small avalanche was also as a result of a warming rock band. It happened right in front of us as we were headed towards it, sweeping across the tracks we had made on the way in. We were already reversing our tracks and would have been right back at this spot in no more than 5 minutes, luckily we had stopped to sort some gear! It would not have buried anyone but some of those heavy snow clumps would have given a good bruising!

Take nothing but litter, leave nothing but a cleaner Drakensberg.

Please login or register to view the images attached to this post.

The following user(s) said Thank You: ghaznavid, Papa Dragon

Please Log in or Create an account to join the conversation.

More
06 Apr 2017 10:58 #71294 by Macc
Replied by Macc on topic Avalanche
My sister was in base camp for the 2015 avalanche on Everest and what surprised me most from her recollection, along with some others, it that the avalanche isn't just snow, it picks up all kind of debris including rocks the size of cars and throws them down the mountain.

Also once the ground had settled the air is full of fine snow 'dust'. This is actually hugely dangerous as well because firstly of all, you can barely see a thing which could cause a very unfortunate miss-step, and secondly you have to wear goggles to avoid snow blindness and have to cover your mouth and nose to avoid breathing in the snow, which can cause a whole bunch of issues (can't remember the terms). Then to add to that your warm breathe from your covered up nose and mouth tend to fog up your goggles which means your visibility drops dramatically....not a fun place to be.

"The three rules of mountaineering: It’s always further, taller and harder than it looks."

Please Log in or Create an account to join the conversation.

More
05 May 2017 20:12 #71498 by intrepid
Replied by intrepid on topic Avalanche
One of the highways in the Canadian Rockies is currently closed due to this avalanche:

www.cbc.ca/news/canada/edmonton/avalanche-closes-icefields-parkway-lake-louise-1.4100869


This spectacular avalanche run-out was filmed at the end of April, also in the Canadian Rockies;

Take nothing but litter, leave nothing but a cleaner Drakensberg.

Please login or register to view the image attached to this post.

Please Log in or Create an account to join the conversation.

More
07 May 2017 20:30 - 07 May 2017 20:32 #71510 by supertramp
Replied by supertramp on topic Avalanche
Hi guys,

Thanks for this info, a very interesting read.

During a hike last year July, about a week after the heavy snowfall in the Berg, my girlfriend and I came across this evidence of a recent avalanche whilst attempting to ascend Mlambonja Pass.


The one "chunk" of snow at the bottom right corner was easily 1m in diameter :woohoo:


A close-up


The debris field can be seen to the left of our camp.


Out of interest, has anyone seen / experienced anything likewise in the Berg? Would this be common or more of an isolated incident? I have not done that many snow hikes in the Berg so I'm not sure. If so, are there certain passes that, due to the lay of the cliffs that might be more prone for this to happen? This specific location at Mlambonja didn't strike me as special or perhaps someone can identify some characteristics from the photo?

Your thoughts and comments will be appreciated :)

Please login or register to view the images attached to this post.

Last edit: 07 May 2017 20:32 by supertramp. Reason: Addition
The following user(s) said Thank You: JonWells, ruthtbl, Andreas, WarrenM

Please Log in or Create an account to join the conversation.

More
08 May 2017 22:13 - 09 May 2017 00:15 #71518 by intrepid
Replied by intrepid on topic Avalanche
Thanks for that post supertramp, found it highly interesting. Avalanches in the Berg have barely been on my radar previously. Its only since living in Canada that my awareness and knowledge has picked up since it is so in your face and frequent here. Though I have had some training and have dedicated books on the subject I'm still a novice, but I'll offer some of my thoughts on your pictures.

As for occurrence, it seems tiny avalanches and sluffs happen in the Berg for a very limited period during or directly after a significant snow event (I base this impression on earlier posts from Deanvdm on this thread). In practice it means human encounters of these is not frequent, possibly even rare, since you have to be in the right place at the right time. In all my years of Berg hiking I don't recall ever seeing anything significant on this scale. Good chance I wasn't paying much attention even if I had seen something. Hopefully this thread will inspire more active field observation and reporting of this kind of thing in the Berg and we will get a better idea from that.

I'd say the avalanche in your photos was a wet release type. It has a specific point of release, fanning outwards from there. So it would not have been a slab avalanche type (which are bigger, deadlier and have more complex and sensitive trigger mechanisms). The chunks would indicate wet and/or consolidated snow. Because its the Berg and snow has a very limited lifespan, but this may have been the result of some day-timing melting and re-freezing at night. It may have happened a few days after the snow event. The south-facing aspect of the slope would have helped preserve the snow for some time and strong winds during the snowfall probably helped deposit the snow more thickly in that specific location, to build up enough mass to form an avalanche. Avalanche types and trigger mechanisms quickly get quite complex, so again this is only a guess, but the avalanche may have been triggered by rocks warming up from the sun. This in turn warms up rocks which are buried under the snow. You can see outcrops and rock bluffs above and around the probable point of origin. It is possible that the avalanche started on slopes above the bluffs but I doubt there would have been enough snow mass for that.

The size is an entry level one and probably would not have buried a person entirely on an even slope. The snow chunks certainly could cause injury of some sort, aside from the obvious complication of being slammed against rocks and other obstacles in the process.

The magic terrain angle for avalanches is 30-45 degrees. Steeper than that and the snow doesn't easily build up enough to form avalanches (rather it comes off in smaller releases/sluffs). It may well be that a good place for Berg avalanches is on the steep, grassy slopes below the dominant cliffs and buttresses of the High Berg, particularly in south facing areas where it doesn't melt quickly enough, and I would think wind-loading in specific terrain features is an ingredient to build sufficient snow mass. Additionally grassy patches that lack supportive features such as boulders and bushes, and that end abruptly in rocky bluffs would be susceptible.

Take nothing but litter, leave nothing but a cleaner Drakensberg.
Last edit: 09 May 2017 00:15 by intrepid. Reason: typo
The following user(s) said Thank You: Andreas

Please Log in or Create an account to join the conversation.

More
Powered by Kunena Forum