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TrogdortheBurninator

Rockfall Question

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Yeah you read it in Climbing or Rock and Ice an issue ago. Basically this type of rockfall is not really an issue above treeline because freeze/thaw and snowmelt induced rockfall are so much more common that they strip off rock so fast (relatively speaking) that the big masses never get the chance to fail.

 

Yes and no. You're right - the freeze/thaw stress cycles occur more frequently and would tend to self-trundle the obvious exterior flakes.

 

But minor faulting in the rock combined with the water flow through it can't be neglected either. Think of a glacier - you've got water systems "communicating" with each other under that ice. If you have a disruption to that system, or something in that system changes, then you might see a result of that on the surface. Glacial outbursts or massive releases of water are an example. Rock is really no different - it just doesn't move quite as fast.

 

So in theory, you CAN have a greater possibility of rockfall after high water inflow - but how MUCH greater is probably not even measurable. And WHEN that greater probability may occur is also not predictable... unless you have the faults and groundwater system mapped to the n-th degree. (I'm not a geotech guy - but my work puts me in close proximity to a bunch of those folks and their reports. Ack.)

 

To me, the type of rockfall mentioned in the first post here isn't something to even concern yourself about. But that's just me. Feel free to go have a beer whenever the need arises!

 

-kurt

 

PS - Without searching for the exact date, it seems like that huge rockslide on the N.Cascades Hwy a couple years ago, just past Newhalem, occured at the end of summer - right after a big rainstorm after a long dry spell. Seems like that was a slab that came down, and not a washout.

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I recently watched a program on discovery on waste water induced rockfall in yosemite, where it specified that hydrostatic pressure from water was the major cause of natural large scale rockfall

 

this must be the glacier point incident...

I'm still not buying it. But don't get me wrong, I don't support the management taking place at the top!

No matter how hard we try, luck is indeed part of the equation. If it wasn't, mountaineering wouldn't be as much fun!! the_finger.gif

fall

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If a rock falls on a silent snafflehound, does it make a sound mushsmile.gif

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For what it's worth rockfall at the Town Walls is always worse during very dry periods. I always assumed that this was due more to the fact that "dry" is a change from the normal and that really anytime there is a big change in conditions the rokfall danger increases.

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If you climb in a gully, a rock might come down and fall on your head. Sometimes snow and ice can fall on your head too. Climb fast. And high.

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Seems like that was a slab that came down, and not a washout.

that is a genuine fact mr nelson..

If you look up on the hill you can see that giant scar in the cliffside. Photo14.jpgshocked.gifbigdrink.gif

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From the Learning From My Mistakes Department:

 

Okay, kinda telling on myself here blush.gif

 

It was May, many years ago. I was teaching ice axe skills at Alpental. We've all seen the rocks littered on Lower International and I kept my team low on the slope, out of the deposition zone. After ice axe arrest practice we went for a "climb", heading for Upper International. Denny Mountain was about to teach me a lesson.

 

At about 2 in the afternoon we were hiking up Lower Intl below the cliffs. Suddenly, a loud report - something like CRACK - was followed by rock and ice careening toward my team. Everyone danced and dodged, and somehow no-one got hit. The one that really stays with me is the rock, approximately the size and shape of a car tire, spinning violently on end, accelerating as it passed between members of my team. It was sickening.

 

Little ol' Denny Mountain swatted my butt and sent me home with my tail between my legs. frown.gif

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Decending Johannesburg, I finished one rappel where it really looked like it was pretty certain that the rope would cause rockfall when we pulled it. Ordinarily, I'd clip into the next rap anchor while waiting for partners to descend. I didn't like the location at all, so I walked right on a ledge and built a temporary anchor under the lee off a projecting rock. We all clipped to that. When we pulled the rope, a positive rain of rocks scoured the rap station to my left. I guess I made a good call in that one.

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Oh, this is kinda like the "Close Calls" thread. I couldn't post this experience in that thread b/c it wasn't really all that close. But it was a rock fall.

 

A couple of years ago I was climbing with my favorite liberal friend, Greg W, at Squamish. I was leading a pitch with a bit of exposure. All of a sudden, that sickening CRACK sound sounded out. I actually scrambled over and scrunched down under a teeny tiny little itsy bitch scrub brush. Even as I was doing it I thought to myself, "Self, this is not going to save you from anything--you are about to be schmeered into the side of this rock forever."

 

Turns out, the rockfall was right across the gully/chasm from me (loud sound, no rumble on my side). I could see the puff of smoke and the fresh scar. Amazing and beautiful as it was scary.

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I guess I made a good call in that one.
Yikes! Uh, yeah, I'd say so thumbs_up.gif

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There is this one rap station on Prusik that is actually pretty prone to rockfall, if you happen to go that way. I missed getting smacked by a 6 inch rock, by a couple feet. Had I been really smart then, I would have put a carabiner on the rap station to redirect the pull of the rope and pulled from the side where I had everyone else standing.

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I'd think rain is a major cause of rockfall both above and below treeline. Studies have shown that high water pressure during and after rain storms plays a major part in slope failure (including bedrock), and it is not too difficult to imagine that water surface runoff destabilizes loose rocks and boulders.

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magnitude and frequency change with climate for a maximum following deglaciation but even today there are rain-triggered rockfalls of all magnitudes at a wide range of frequencies in the mountains.

 

isn't it fairly commun to find reference to rockfall during rainstorms in the climbing litt.

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Rainfall triggered = low frequency, higher magnitude

Frost triggered = reverse.

 

Since it only takes a small rock to kill you ---> worry about the latter and not the former

 

Of course there is a third category of rockfall too...

 

Meteor.JPG

 

Also most common during showers.

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Shit happens all the time. Not to be flippant in a sad time. (RIP to all friends of wild places and wild mountains)

 

It is always a crap shoot when you are in the mountains. We choose to go into a hazardous environment and sometimes things don't go our way. I've almost been taken out several times by rockfall. I have friends who haven't survived their good times in the mountains. It has really made me think about why I go and what I do in the mountains. But like many of you, I can't explain it but I have to do it, I just hope I make it out alive each time I go.

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Rainfall triggered = low frequency, higher magnitude

 

i am not sure this holds where it rains a lot. freeze-thaw also probably makes material available for rain to trigger.

 

Frost triggered = reverse.

Since it only takes a small rock to kill you ---> worry about the latter and not the former

 

hmmm. need audio sensors in some choice gully during rainfall before deciding what to worry about.

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i think druL was referring to the probability of it all.

but, seriously, what kind of shithole gullies do you think are choice?

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i am just not sure that the probabilty of rain induced rockfall is negligeable everywhere i.e. summit slope of little tahoma, boving on dtail, various descent gullies, etc ...

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Decending Johannesburg, I finished one rappel where it really looked like it was pretty certain that the rope would cause rockfall when we pulled it. Ordinarily, I'd clip into the next rap anchor while waiting for partners to descend. I didn't like the location at all, so I walked right on a ledge and built a temporary anchor under the lee off a projecting rock. We all clipped to that. When we pulled the rope, a positive rain of rocks scoured the rap station to my left. I guess I made a good call in that one.

 

Erick and I also pulled down some blocks while pulling rope descending Johannesburg, but we figured that was all just part of the program on that thing.

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