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Avalanche terrain travel

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Avalanche terrain travel

Postby apasquel » Fri Apr 26, 2013 6:16 pm

I have very limited experience on slopes...but what I see on TRs and what I have learned seem to contradict. Everything I "know" says that while traveling on slopes with potential avy danger, you want to travel one person at at a time until reach safety zone...however, every mt. Shasta report I see climbers climbing side by side or on this site you the same thing on different 14ers...which got me thinking, many of the reports I've read in the last few years have many experienced, very competent backcountry travelers on this site traveling next to a partner in their TR. my assumption is...there are times when you can travel slopes together? I don't know...but I do know this, I am climbing sneffels next week and I would love your input on how to approach the lower slop and lav col with a partner. Can anyone give me a number on how steep the slopes are? With the next week weather forecast (really nice but warm trend), what should I be most concern with? I would imagine time and getting off the slopes before it gets too warm...

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Re: Avalanche terrain travel

Postby COBuckeye » Fri Apr 26, 2013 7:51 pm

apasquel wrote:my assumption is...there are times when you can travel slopes together?

Yes, there are times, depending on the avalanche risk level, when it is relatively safe to travel together. Most people only climb straight up avalanche terrain when the risk is low, which may explain why you see a relatively high percentage of TRs with people traveling together. When avalanche danger is high, most will minimize the number of people exposed to the danger and the time exposed to the danger. Usually this means taking the path of least resistance across the danger zone, one at a time, as fast as safely possible.

apasquel wrote:Can anyone give me a number on how steep the slopes are?

I don't know, sorry.

apasquel wrote:With the next week weather forecast (really nice but warm trend), what should I be most concern with? I would imagine time and getting off the slopes before it gets too warm...

Check CAIC website for the avalanche forecast. You are correct that you want to be off the higher angled slopes before it gets too warm. A very general rule of thumb is: If you are sinking in to warm wet snow 3-4", it is time to get off quick.

This is all just my two cents, please do not make personal safety decisions based on some unqualified advice given on the Interwebz.
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Re: Avalanche terrain travel

Postby MonGoose » Fri Apr 26, 2013 8:09 pm

apasquel wrote:Can anyone give me a number on how steep the slopes are?


http://caltopo.com/map.html#ll=37.99805,-107.78366&z=15&b=t&o=r&n=0.25&a=sf

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Re: Avalanche terrain travel

Postby apasquel » Fri Apr 26, 2013 8:54 pm

MonGoose wrote:
apasquel wrote:Can anyone give me a number on how steep the slopes are?


http://caltopo.com/map.html#ll=37.99805,-107.78366&z=15&b=t&o=r&n=0.25&a=sf


sweet! Thanks

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Re: Avalanche terrain travel

Postby rickinco123 » Fri Apr 26, 2013 10:38 pm

I would love to get some feedback on how accurate people think caltopo is. If you look at chair 1 at Loveland Ski Area or the SW Couloir on Coon Hill, both show no color on the heat map but both have terrain over 40 degrees. It looks pretty inaccurate to me. Anyone know what technology they are using to get those slope angles?

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Re: Avalanche terrain travel

Postby HuskyRunner » Sat Apr 27, 2013 8:08 am

apasquel wrote:, every mt. Shasta report I see climbers climbing side by side


The snow pack in CA, coastal mountains in general, is much different than our Rockies snowpack. You need to understand regional and local environmental conditions to have any chance of understanding avi potential.
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Re: Avalanche terrain travel

Postby shaunster_co » Sat Apr 27, 2013 8:31 am

rickinco123 wrote:I would love to get some feedback on how accurate people think caltopo is. If you look at chair 1 at Loveland Ski Area or the SW Couloir on Coon Hill, both show no color on the heat map but both have terrain over 40 degrees. It looks pretty inaccurate to me. Anyone know what technology they are using to get those slope angles?


I have printed out a few color versions of the CALtopo which were an overlay in Google Earth (KMZ export) and took it with me to a few of the areas I regularly go to verify slope angles. Some of the areas were; RMNP Dragontail Couloir / apron, Andrews Glacier via The Gash, Caribou area (Old Baldy area), Corral Couloir / Tyndall Tarn and an area near Thatchtop. I took inclinometer readings on the overlay that I could positively identify points and terrain features. By and large, the average is close to what CALtopo shows - but much of the shading is off by several hundred feet in areas - and others which certainly averaged >20 degrees, were shown as a higher value. It is by no means exact. Also, as we have just witnessed recently it does not account for the run out areas that are possible in slabs. In other words - it shows slope angle vaguely, but not all danger areas. Because snow can obscure actual slope angle of terrain, I did take a few of these readings when there was no snow, but found the same results.

I found it to be illustrative for rough slope angles, but not something I would use to evaluate terrain for anything other than pre-planning. I certainly wouldn't use the data solely for planning a route, but rather one of several tools in the arsenal. I too would be curious of the technology though. It does provide a good reference, but in my opinion not exact.

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Re: Avalanche terrain travel

Postby Magnum420 » Sat Apr 27, 2013 8:50 am

or the SW Couloir on Coon Hill


If you are talking about the i70 bypass couloir on Coon Hill, I think its pretty accuratly shaded on the map. Though, thats more south facing, not real familier with the sw facing slopes.
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Re: Avalanche terrain travel

Postby mattyj » Sat Apr 27, 2013 12:11 pm

As the guy behind CalTopo I normally don't like interjecting myself into conversations like this one, but as I still have mixed feelings about the slope shading layer, here goes. First and foremost,

shaunster_co wrote:I found it to be illustrative for rough slope angles, but not something I would use to evaluate terrain for anything other than pre-planning. I certainly wouldn't use the data solely for planning a route, but rather one of several tools in the arsenal.


is exactly right. The slope shading is intended to assist with high level decisions and is not a bulletproof or error free tool, especially for micro-level terrain choices.

Technology wise, the slope shading is built off Digital Elevation Models (DEMs) from the USGS, in this case the National Elevation Dataset. The NED is supplied at a single resolution (approx. 10 meter horizontal) for the entire US, but different areas have different source resolutions. On one end of the spectrum, Rainier is clearly built off LIDAR data as the DEM captures every twist, turn and jumble in the glacier. At the other end is Icebox Canyon in Zion. The topo shows a smooth walk into the canyon where there is actually a 3 pitch rappel over a cliff. The DEM is clearly either based on the same survey data as the topo or interpolated from its contour lines, as it matches this error exactly.

I used the gdaldem utility to generate the actual shading. Since it doesn't properly handle datasets with different X and Y scales, I warped the DEM into the web mercator projection used by google maps, broke it up into 7.5' slices, and varied the scaling for each one as the mercator projection's scale changes with latitude. This means that technically the shading will be less accurate at the top and bottom of each 7.5' slice, but the actual error is too small to matter. There's also no one "definitive" algorithm for computing slope from an elevation grid, but again, well within our margin of error.

The resolution of the slope layer roughly matches the source resolution of the DEM; while it's probably pixel-accurate for Rainier (excepting glacier movement), I do think that it can, in some cases, imply a greater resolution than what actually exists. Unfortunately there's no metadata associated with the DEM that would allow me to determine the actual source resolution in each region and vary the shading accordingly.

The shading *should* be an accurate reflection of what you would get by counting contour lines and measuring distances with a topo. The CalTopo contour lines are built off the same data, so one of the things I do is turn the contour layer on and see if it roughly matches the USGS map; unfortunately when it diverges there's no way to know why or which is more accurate. Note also that the new USFS maps have contour lines based on DEMs, rather than re-using the contours from USGS topos.

So at a minimum, the possible errors include 1) human error by me, which should be systematic across the entire US 2) survey errors or other inaccuracies with the source elevation data 3) small rollers that are still big enough to release but too small to show on a topo map and 4) variations between summer ground angle and the snowpack surface. The last one is especially prominent near ridges, where windloading can completely transform an otherwise benign slope.

With the exception of ridges and tiny terrain features I've found it to be pretty accurate for the areas I have access to (California). That said, every time I read about a slide I find myself running to the slope layer to see if the danger was accurately portrayed - often difficult to do as the topos from incident reports only mark the bounds vaguely - because I have this lingering fear that I may be putting out a product that's doing more harm than good by giving inexperienced skiers a false sense of confidence. Some people have certainly told me they think it's a bad idea. One thing that does eat at me is that it doesn't take much to trigger a slide, and small starting zones don't visually stand out the way a giant 40 degree slope does - my brain naturally wants to go "that doesn't look bad, there's just a few bits of red here and there".

Going back to the shading layer being roughly equivalent to computing slope off a topo with a ruler, there are a couple comments made on here that concern me, because they imply a greater level of inaccuracy than I think should exist. I'm not trying to defend my map layer or argue with anyone, simply seeking feedback and more detail.

shaunster_co wrote:much of the shading is off by several hundred feet in areas


can you tell me where, and is that based on the topo or a Google Earth printout? In my experience Google Earth isn't super accurate about where it places overlays on steep terrain, but the errors there shouldn't account for a 200' horizontal difference.

rickinco123 wrote:If you look at chair 1 at Loveland Ski Area or the SW Couloir on Coon Hill, both show no color on the heat map but both have terrain over 40 degrees.


I'm not familiar with either area, but I see plenty of 35-45 terrain skier's right and a little left of chair 1. A quick ruler calc of an unshaded area skier's left of the chair has 450' horizontal feet between major contour lines which is 24deg. Again not looking to argue, but I'd really like some more specifics about areas you think are significantly off. Can you take a screenshot?

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Re: Avalanche terrain travel

Postby shaunster_co » Sat Apr 27, 2013 2:11 pm

Matt,

First off I think the map tool is a great resource. I hope it didn't come off any different. I was just implying that the tool gives a reasonable average in terrain. If anyone is using it to plan a route with GPS tracks in avy terrain - I was suggesting to use it as one of many tools but not rely exact accuracy of the slope angles.

Most of the slope angles in RMNP - especially on the couloirs and glaciers are a bit off, but we would expect that - I think, given that the snow depth changes considerably from the actual earth terrain. It was actually a question I had in the mapping, being; does Google Earth, USGS, GIS, etc use the actual earth terrain, or 'surface' terrain when mapping? Especially in areas where there are more permanent snow features, or at least most of the year? I came to the conclusion that they use actual surface terrain given that water features are done the same way, but it is still a question that nags me in snow terrain.

One area I am perplexed by is Bald Mtn, a subpeak of Old Baldy from the Caribou townsite approach. Often times I use this route to gain entry to the higher terrain. I took a screen shot of the areas I did a slope angle back in February, with a KMZ overlay of Caltopo. This was the area in particular I noticed that the shading may be off. This is an area that is more less a permanent snow feature. Even in August I cannot takes slope angle measurements at the actual surface - since much of it still has snow. I am assuming that the snow field creates the discrepancy? The discrepancy is also on the topo map - to some degree. The areas I would have thought should be orange indicating an angle more than 30 degrees do not appear on the overlay. I figured perhaps a certain percentage of terrain had to be at a certain slope angle for it to register. Or possibly that the metes and bounds in the area might be off (but I am assuming that is unlikely), or perhaps the overlay in google earth is just off (more likely?).

Again, none of these discrepancies really concern me because I have used Caltopo in conjunction with other things. I think it serves a great resource to predict where certain red flags would be. My concern is that people might use it to plan a route within a contour line of precision. Thanks for the clarification on the ins and outs of the mapping software.
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Re: Avalanche terrain travel

Postby rickinco123 » Sat Apr 27, 2013 5:03 pm

mattyj wrote:As the guy behind CalTopo I normally don't like interjecting myself into conversations like this one, but as I still have mixed feelings about the slope shading layer, here goes.

Thanks for spending the time to post here, I didn't expect to get an answer straight from the source, Wow! Thank you for the web app, it is a nice resource. I hope I didn't sound too negative. I didn't realize this was mostly working of off contour line data and satellite measurements.

I completely understand how this works now, with your explanation it makes a lot of sense to me.

Don't beat yourself up for how people may misuse your data, no one tool should be used for trip planning and terrain travel anyway. If I have the "where with all" to post up slope angle gps points that I find are significantly off I'll send them to you if you want them.

Shaunster, thanks for doing that work with the GPS coords and the slope angles.

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Re: Avalanche terrain travel

Postby sam » Sat Apr 27, 2013 5:30 pm

Matt,

I just want to thank you for Caltopo, it is a great tool in many aspects, everything from trip planning, GPS tracking as well as I use it for SAR

thank you and keep up the great work!
scott

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