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this just in
climber
Justin Ross from North Fork
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Apr 20, 2015 - 07:53am PT
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Scary. Glad to hear that it seems like everyone is alright.
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pyro
Big Wall climber
Calabasas
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Apr 20, 2015 - 08:20am PT
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damn rock fall!
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sac
Trad climber
Sun Coast B.C.
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Apr 20, 2015 - 08:40am PT
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I heard, and came straight here.
Was out re-habbing a climbers trail that was wiped out by falling rock!
Amazing no-one hurt.
Creeps me out man.
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Evel
Trad climber
Nedsterdam CO
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Apr 20, 2015 - 08:45am PT
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Ho Man that's a lotta rock!
Glad to see no reports of injury. Hope it stays this way.
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Oplopanax
Mountain climber
The Deep Woods
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Apr 20, 2015 - 08:58am PT
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I was climbing in the Bluffs at Tunnel Rock. We heard two rock falls before the big one. The first one, around 11:20 we thought might be new routers trundling, and we talked about what a dumbass move it was to trundle on a sunny weekend. The second one came around 11:40 and was the same size of sound as the first and we looked at each other and wondered if it really was trundling or not. Then the big one dropped and we knew it wasn't trundling.
We hiked up to the top of the Bluffs and Barley's obscure Nighthawk Moss crag (great routes there btw, Robin showed up while we were climbing, and claimed we were doing second ascents) and got a good view of the fresh scar.
In addition to the big dirty scar at the top of Chilkoot Passage that's claimed most of the attention, there is also a second, paler scar just down and to the right, in the vicinity of the second-last pitch of Yukon Gold and The Temptation of St Anthony and in the vicinity of the original Zodiac Wall. Anyway you can see fresh new rock scars on the slab below the arching corner that these routes take.
I believe one of the earlier rockfalls was the one that made this scar, and that this may have removed some of the support for the block that made the larger scar.
EDIT: got a better view in a pic from another angle of the Yukon Gold area. The WPoS pillar is still there, but the 11a pitch above (the route's last pitch) looks to have substantially altered.
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Oplopanax
Mountain climber
The Deep Woods
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Apr 20, 2015 - 11:28am PT
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Better annotated photo, thanks to Mike for the before and after!
Note lowest scar: green outline, brand new dihedral!
Then probably the orange stuff failed in sequence, and this removed enough material for the red block to go as a single mass.
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Big Mike
Trad climber
BC
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Topic Author's Reply - Apr 20, 2015 - 12:05pm PT
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Drew you stole my thunder! ;)
Here's the original before and after.
After, little further out
Before from the bluffs
Original after
Original before
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TheSoloClimber
Trad climber
Vancouver
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Apr 20, 2015 - 12:20pm PT
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It looks like that massive block underneath it is just waiting for a reason to go as well.
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Big Mike
Trad climber
BC
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Topic Author's Reply - Apr 20, 2015 - 12:31pm PT
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From way higher up, massive block realized and rotated out from the face. I could see debris at the toe of the block ravelling off, sensing something big was about to happen. The sound was incredible. Anybody who has climbed Angel's Crest knows that the sound echos off across the North Gully and the North Walls. At first I saw the base of the block moving and dust clouds forming. I've watched more than my share of rock fall and landslide videos through school and work and for fun, but this was a first experience for me.
It was hard to judge how close it was to me. The view of the mountains was momentarily blocked by the free-falling granite. There was no rotation, just one monster chunk of granite aimed straight down. I looked up and Mark, jaw-dropped and speechless. Once the block hit the forest below, a huge plume of rock dust engulfed the area below. The volume of rock is estimated at 1000-5000 cubic metres. I couldn't see the parties below at this point but hoped that they were ok. Richard So
http://richso.blogspot.ca/2015/04/angels-crest-and-zodiac-wall-rockfall.html
edit
ya Nathan. could be.. the boot looks sketchy too though and it's still there...
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Impaler
Social climber
Oakland
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Apr 20, 2015 - 01:02pm PT
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I'm really glad this pitch was far enough to the left. Probably the best dihedral pitch on the planet.
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Big Mike
Trad climber
BC
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Topic Author's Reply - Apr 20, 2015 - 01:07pm PT
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The base of your pic is the impact zone.
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Big Mike
Trad climber
BC
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Topic Author's Reply - Apr 20, 2015 - 01:18pm PT
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I think all that brown stuff is evidence that water and dirt was getting behind there for awhile. If you look at Dru's orange and green outlines, the rock fractures there are clean. So I think that thing was probably just sitting there being held by the flakes and pillar below it.
The upper right corner of the block fracture looks fairly clean too so, that was probably holding it as well.
Gstock? :)
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Big Mike
Trad climber
BC
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Topic Author's Reply - Apr 20, 2015 - 01:36pm PT
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Supercrop of the scar
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Big Mike
Trad climber
BC
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Topic Author's Reply - Apr 20, 2015 - 01:55pm PT
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Before supercrop
Notice all the dirt on the slope below? and in the groove above it. This thing's been lurking for awhile I bet.
It would appear that the block slid over/impacted that slab. If that lower chunk was about to go, one would think that it would have gone then??
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Oplopanax
Mountain climber
The Deep Woods
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Apr 20, 2015 - 02:23pm PT
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Hard to blame this one on rainfall and pore pressure along the fault since we're in the middle of sunny and dry conditions.
Given the dirt behind the main scar, I think root wedging from the trees on the ledge might be to blame. We're in the middle of spring and the trees are in the middle of their annual growth spurt, putting on mass in their roots too.
Of course, the response time to glacial unloading can be tens of thousands of years, so in our time scale, things can fall off for no immediate cause. They are responding to an event (deglaciation) thousands of years ago.
Hydraulic conductivity varies along joints too. But it's hard to state with a straight face that the pore pressure varies enough that this thing popped off now in response to record rainfall months ago.
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Big Mike
Trad climber
BC
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Topic Author's Reply - Apr 20, 2015 - 02:28pm PT
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Maybe a combination of factors Drew? Perhaps the roots wedged it out enough to fracture the support structure below?
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gstock
climber
Yosemite Valley
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Apr 20, 2015 - 03:45pm PT
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You guys are up against the problem we often deal with in Yosemite in terms of rockfall triggering, namely that several possible environmental triggers are present (water, root wedging, etc.) but there is no "smoking gun". Plenty of Yosemite rockfalls occur on bluebird days when you just wouldn't expect it.
The fresh scar in Mike's photos clearly shows weathering and staining indicative of probably decades of seepage, plus some residual soil. This suggests that the block was partially detached for quite awhile.
However, I'm most intrigued by the reports of precusor rockfalls that occurred in the cleaner rock beneath the big block; if that was indeed the case, the partial detachment and weathering of the big block may have been mostly irrelevant, as the block was undermined by smaller rockfalls that fell for some other reason.
Speculation from afar...
In case you get really interested in this stuff, the Yosemite rockfall database and a paper we wrote on the progressive Rhombus Wall rockfalls in 2009-2010 are available here: http://www.nps.gov/yose/learn/nature/rockfall.htm
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Big Mike
Trad climber
BC
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Topic Author's Reply - Apr 20, 2015 - 03:52pm PT
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Greg there are reports of new routers hearing small gravel sized rocks falling last week. They thought someone was throwing rocks from the top!
Perhaps the roots made enough space for the medium behind the block to escape?
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Oplopanax
Mountain climber
The Deep Woods
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Apr 20, 2015 - 04:00pm PT
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Causes of rockfall are of professional interest to me.
In this case there definitely were two separate, smaller, audible rockfalls in the half hour before the big one.
It's also true that Paul M reported small rocks falling while new routing in the area over the last week.
This does point to progressive loss of support for the big block that ultimately fell, and it also suggests that frequent, small rockfalls can serve as a useful indicator for a future larger rockfall, which is an easy idea to convey to non-geoscientists.
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