Massive rockfall - Waterfall route

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Dingus Milktoast

Trad climber
Minister of Moderation, Fatcrackistan
Dec 7, 2017 - 05:55am PT
^^^ Keeping it civil over here, Boss!

DMT
Contractor

Boulder climber
CA
Dec 7, 2017 - 06:10am PT
We were just across the wall during both rock slides on "New Dawn". I was cold in my sleeping bag during the predawn hours and shortly after the sun hit the wall I was taking my shirt off. I've never been exposed to such rapid temperature changes.




gstock

climber
Yosemite Valley
Dec 7, 2017 - 02:26pm PT
According to Yosemite's rockfall database, root wedging accounts for about 7% of documented rockfalls, although there could be some unidentified root-related events hiding within the "unknown" and "unrecognized" categories. Unknown means that no information about environmental conditions exists (usually rockfalls from the late 1800's), and unrecognized means that there were no obvious environmental triggers. Precipitation is the dominant trigger in terms of the number of rockfalls, but not dominant in terms of the volume of rockfalls.

Triggers for Yosemite rockfalls &#40;1851-2011&#41;.  Data from Stock ...
Triggers for Yosemite rockfalls (1851-2011). Data from Stock et al. (2013).
Credit: gstock
limpingcrab

Trad climber
the middle of CA
Dec 7, 2017 - 03:09pm PT
That's a cool chart, thanks for sharing.

Just curious, how do the categories work that aren't mutually exclusive? "Rain on Snow" and "Precipitation" for example.

Is it sort of primary cause, rather than specific cause? Or maybe most influential cause?

No worries if you're busy, just a passing question from the data analysis dork side of me. I like stats.
gstock

climber
Yosemite Valley
Dec 7, 2017 - 04:42pm PT
We tried to be as specific as possible as to the environmental conditions present at the time of the rockfall. So "rain on snow" is really a subcategory of precipitation, but it contains more specific information, should that prove useful later on.

The thing to remember is that these trigger assignations are based simply on environmental correlations, and are not necessarily causations. Identifying triggers also requires some judgement, and that can get tricky. For example, what to list as the "trigger" when a brief rain barely wets the rock and a rockfall happens (say, from beneath a tree) as the sun comes out an hour later?
Big Mike

Trad climber
BC
Dec 8, 2017 - 07:43am PT
Hi Greg, Thanks for all your work. I really enjoy learning about the cliffs where I like to hang.

Cool graph! How does lightning cause rockfall?
'Pass the Pitons' Pete

Big Wall climber
like Ontario, Canada, eh?
Feb 28, 2018 - 08:47pm PT
Well, f*ck me, it's good to still be alive!!
Mighty Hiker

climber
Outside the Asylum
Apr 30, 2018 - 10:04pm PT
It will be interesting to see a photo of the rockfall area from the spring, once it dries out, to see what can be seen, also if there's been further rockfall there.
ground chuck

Ice climber
Olympia
Apr 30, 2018 - 11:28pm PT
any free swag in the rubble? like bolt hangers?

maybe a rotted but still usable sling?

busted cam that can be salvaged for parts or recycled alumonum?
7SacredPools

Trad climber
Ontario, Canada
May 1, 2018 - 07:25am PT
Hey Big Mike. Lightning is hot! It blows up trees by the rapid expansion of the moisture in the wood. I would think the same could apply to rocks...

Interesting graph but what's the difference between "unrecognized" and "unknown?" Does "unrecognized" mean the rockfall could be attributed to one or more of a number of factors?
gstock

climber
Yosemite Valley
May 1, 2018 - 02:35pm PT
Lightning has been known to explode rocks on summits (and also melt them), so it's reasonable to think that it could trigger rockfalls. It hasn't happened very often in Yosemite though.

We can't measure rockfall triggering directly, so we make inferences based on the environmental conditions present at the time of the rockfall. For example, if a rockfall occurs coincident with an earthquake or an intense rainstorm then assigning a trigger if fairly easy.

"Unknown" means that we have no information on what the environmental conditions were at the time of the rockfall, so we cannot even speculate on a trigger. Most of the rockfalls in the database that have "unknown" triggers happened a long time ago and are based on very cryptic reports.

"Unrecognized" means that even though we do have good information on the environmental conditions at the time of the rockfall, there still isn't an obvious trigger. If a rockfall happens on a clear, mild day with no seismic activity, what is the trigger? We will say that it is "unrecognized", meaning that we really don't know.

As a scientist, "unrecognized" is the most interesting category because there is a lot to learn there.
gstock

climber
Yosemite Valley
Jun 14, 2018 - 09:40am PT
For anyone interested, here is a short (and hopefully readable) paper on our analysis of last year's rockfalls from El Capitan. I find the sequence of rockfalls shown in Figure 2C especially fascinating.

http://www.geosociety.org/gsatoday/groundwork/G374GW/GSATG374GW.pdf
looking sketchy there...

Social climber
Lassitude 33
Jun 14, 2018 - 10:02am PT
Thank you for posting the link to this very interesting and informative paper.
Climbnrok

Trad climber
LA
Jun 14, 2018 - 04:58pm PT
Anyone have a good photo of the "outward displacement" section?
gstock

climber
Yosemite Valley
Jun 14, 2018 - 06:05pm PT
Credit: gstock
xCon

Social climber
909
Jun 14, 2018 - 06:17pm PT
is that the plate that's moved out 20cm?
neebee

Social climber
calif/texas
Jun 14, 2018 - 09:54pm PT
hey there say, gstock... wow, neat... thanks for sharing... :)
CAC

Gym climber
Clairemont
Jun 14, 2018 - 10:21pm PT
The last slab to go was 8m thick... yikes!
skywalker1

Trad climber
co
Jun 14, 2018 - 11:54pm PT
Kinda makes me think of the nipple pitch and the white circle...

S...
ground chuck

Ice climber
Olympia
Jun 15, 2018 - 01:57am PT
spooky cracks
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