Messages posted by : ise
Profile for ise > Messages posted by ise [1815]
Not really, it depends on the snow, it would exceptional to easily pick out tracks though. Really if it does track it can get confusing which is why large searches tend to use flags or poles to mark contact points and so on.
It's great in practice as well, that's why it's what you do and it's what you practice.
Avalanches vary in size and shape. A dry snow avalanche can move at up to 225mph but that's vanishingly rare outside the greater ranges. A wet snow slide would be more like 20mph. The normal alpine avalanche isn't really close to 120mph. On average with a dry slab avalanche you're looking at a speed of around 70 miles an hour.
A primary search is the part of the process we're using a transceiver to detect any signal at all. Once that's detected we go to a secondary search pattern which should get us in 2 or 3 metres before finally going into a pinpoint search using probes etc. Surface traces can be useful but in practice you need to consider that people get separated from kit, in fact in an ideal world if you're caught in a slide you want to release from bindings and drop your poles. Most people have some experience how far free gear can move in snow. If you witness a slide then you need to try and closely watch for where you last clearly saw people, that's a help for deciding where to begin the search. In fact, the very first thing you actually do after a slide is ensure you and the group are in a safe place. It's the most important thing bar none.
very true, and the lesson from that is that don't want to be searching from below of course. So if you're in a group crossing some suspect terrain you want to look at how you're moving and try and reduce that window for top searches. There's a few transceiver parks in the Alps and it's odd how rarely you see people start from above which is a realistic situation. |
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Early season reported snow depths on glaciers are for accumulated snow that winter, that's why they're the sort of numbers you'd expect at around the one or two metre mark. I can tell you why SLF figures aren't really relevant to glaciers if it helps you though, it's simply because they don't place monitoring stations on the glaciers. You'd not really get too much data relevant to avalanche forecasting so it's not something they systematically do. If you want extend your knowledge of what's happening on glaciers with snow depths and the glacier depth then I can recommend the work done by Zurich University who've pioneered some laser technology to measure depths and density and give better ideas about what we call glacier mass balance which is a better measurement of how well glaciers are doing. There's also the ETHZ glacier monitoring service which has some good data available publicly. The University in Fribourg also publish analysis of snowfall, depth and duration. But these are academic resources and likely of interest only to professionals and you don't really need them to understood what I'm trying to explain to you. You're telling us that you see reports of 4m of snow on a glacier in the early season. I think you're correctly realising this isn't likely which is why you were helpful in warning people to treat them with caution. I'm sure you do understand that glaciers are more than 3 or 4m deep so you know it's not the depth of the glacier you're seeing. Without getting too farfetched then you must see your 3 or 4m figure is : a) measured from an arbitrary point and just means "oh boy, there's a lot of snow up there" b) accumulated snow c) (sorry) not true. And, again correctly, you're sensibly eliminating that it's accumulated snow either because it's too early in the season and/or you appreciate that would be the entire season accumulation at current averages. Obviously ski stations aren't really going to get away with just picking figures out of the air, you know they're not reporting glacier depth because you'd see figures of 5000cm and more so you must see that they're trying to accurately report the actual accumulated snow depth on their glaciers and that's why they report figures around 1 or 2m for glacier snow depths early in the season. And they go on right through the season reporting the amount of that's fallen on the glacier. And we can test this quite easily. We know there's going to be 1 to 2m of new snow on the glacier on December because it is accumulating right now, we expect to see some 3 or 4m by the end of the season and values in between of those during the season. So, here's the report filed by Engelberg on 23.05 this year :
And here, by comparison is one filed in March 2008 :
So what's the depth going to be in late December? Around 1.5m, the same as last year I'd expect. I cannot possibly comment on hypothetical snow reports, I can simply tell you what the snow reports I do have sight of actually say and why figures of 3 or 4m bear no relation to anything that could be measured. If, as the season kicks off, you have an actual copy of a report that says 4m of snow on a glacier somewhere than post it (or it send via my website as I don't always have time to read this) and we'll see if we can work out what they're measuring.
I'm sure it's not a competition :) I spend a few days in the mountains each year myself ) |
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Average glacier depths in their accumulation zones around Switzerland are 70m as I already pointed out. From that you know for certain a snow report of 3m isn't the glacier depth. I'm not able to speculate what a hypothetical snow report may or may not be measuring but if I saw a report in December for, as an example, Zermatt, telling there was 2m of snow on the glacier I would know that was new snow from that winter. So when you see Engleberg reporting depths in December of around a 1.5m (that's the actual recorded, reported historical figure) you're seeing new snow that's fallen in that winter. I can't see why that's surprising, it's snowing right now, the zero isotherm is beginning to settle below 3000m so higher glaciers are accumulating snow. It would surprising if there wasn't a couple of metres of snow accumulated by December. In fact, that relatively low figure of 1.5m for Engelberg reflects a fairly poor start to the last season. It's the same for the 1.7m that Laax reported in December last year. In point of fact, neither Engelberg nor Laax ever reported more than 3m for the whole of the previous season, the highest measure was 3m or so in April which represents the season accumulation. And, physically, practically, how is it measured? By putting a pole in the snow of the glacier at the start of the winter, or more likely around now, and seeing how far up the pole the snow goes. The first reports for Engelberg last season were 0cm lower and 45cm upper in November then 48cm/123cm in December, there's nothing I find surprising about that. |
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While glacier mass balance is decreasing in many places I don't we've quite arrived at a point where the depth in the accumulation zone is down to three metres. Glacial depths in Switzerland are around 70m on average IIRC.
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You need to check that or better understand the practical implications as there is a difference between perpendicular range and inline range. The pieps has a good range, in optimum conditions a perpendicular range of around 40m IIRC, but it doesn't alter what we think of as standard search protocols as a guide, leader or avalanche trainer would teach on a course as you rightly recommend. Pieps and the Pulse manuals suggest fairly aggressive parallel search distances of around 50m IIRC ie a working range of a 25m search distance which is rather less than 50 or 60m. Which is a distraction and the sort of distraction which I find rather dangerous. Practically, a group would not expect to find a debris cone of the sort of size where this becomes an issue where the group itself is of a size to make a difference. Real world group sizes, and skills, along with real debris sizes mean you're nearly always better using a single searcher for the primary search and deploying your additional people to triage and fine search. I don't have any intention at all of trying to recall in an incident what the effective perpendicular ranges of half a dozen sorts of transceivers are and adjust a grid accordingly and neither should you. This is why we have standard protocols, teach them and use them, it's easier and it's safer. If you want to improve your ability to move safely in winter environments I'd suggest concentrating on this type of decision making and not get caught in the sort of datasheet comparisons of transceivers another ski forum seem to find so fascinating :-) If you are in a group with mixed gear, and you're dealing with someone that's memorized the data-sheet and not really understand the problem at hand, then I suggest you bury a device and get the group to walk towards it in a straight line each stopping as they get first signal. Try it again with the transmitter aligned differently and/or swap batteries around if they're not getting it. if that's not working out then I'd reserve their skills for digging in the event of a slide :-) |
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That's not correct, old analogue transceivers may have a reception range up-to 60m. Modern devices manage nothing like that. In practical application you would assume a range of no more than 30m.
You simply would not do that. A standard group primary search protocol would search not more than 10m from the edge of the debris field with not more than 20m between searchers. This would apply to analogue or digital devices. I'd also submit that were the range reliably 60m, which it is not, then you would search 50 metres from the edges and 100m between searchers to achieve maximum coverage, those proportions are incorrect and fail to factor for adverse antenna alignment, deep burial or weak batteries. In practice you would adjust these distances based on the number of searchers. With enough people I would organize a group primary search at around 10m range, ie 5m from edge of debris with 10m between searchers. However, in practice I would consider using a single person to make a primary search if they entered the debris from above and it was not more than around 50m wide, I would strongly favor this protocol in the event of multiple burials. For a single searcher you would travel at 90' to the falline across the debris with the widest search not more than 10m from the edge of the debris field, moving up or down to give not more than 20m between traversals. Also, a debris field 120m wide would be an avalanche of devastating proportions, I would suggest a group on the mountain would be overwhelmed by such an incident and would be simply unable to mount an effective recovery |
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I think you're right, I'd guessed around £400 so that's a good price and I think nicely cheaper than renting a car and all that hassle.
very good tip, it's not obvious at all and it was seeing other people use it that tipped me off as well. |
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Profile for ise > Messages posted by ise [1815]