Massive rockfall - Waterfall route


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Social climber
Sep 29, 2017 - 03:12pm PT
hey there say, skcreidc... oh, yes! very nice (the study of yosemite, adn rock)... i DID get to see that...

thanks for sharing...

forgot, who shared it, when i saw it, but, yes, good share...

thank you so much.... done very nice and in good taste, etc...

right here, right now
Sep 29, 2017 - 03:24pm PT
EC offered:
I found the GIS maps quite interesting in regards to this stuff, especially the one on the time of year historically that rock fall occurs.

Yes, EC, from page 9, perhaps some useful, and certainly interesting data for climbers:

From the 96 page document:

Social climber
The internet
Sep 29, 2017 - 03:43pm PT
Insane. Best wishes for the family of the unlucky one...
rick sumner

Trad climber
reno, nevada/ wasilla alaska
Sep 29, 2017 - 05:04pm PT
Rockfall in this area is nothing new. In the spring of 1974 i was racing up east buttress of middle cathedral with my freind Bill when a very loud boom of rock fall interrupted our concentration. Clouds of dust quickly obscured the east end of El Cap then the meadows. Although not as large as this exfoliation a sizable scar was visible some time later when the dust lifted.

Trad climber
Leading Edge of North American Plate
Sep 29, 2017 - 06:13pm PT
Rockfall in this area is nothing new

Yes, it has been going on for 1,000s of years...

From Greg Stock...

from the same presentation...

for more information on this age dating method...

Eiszeitalter und Gegenwart Quaternary Science Journal 57/12 179209
Hannover 2008
Surface exposure dating with cosmogenic nuclides

Abstract: In the last decades surface exposure dating using cosmogenic nuclides has emerged as a powerful tool in Quaternary geochronology and landscape evolution studies. Cosmogenic nuclides are produced in rocks and sediment due to reactions induced by cosmic rays. Landforms ranging in age from a few hundred years to tens of millions of years can be dated (depending on rock or landform weathering rates) by measuring nuclide concentrations. In this paper the history and theory of surface exposure dating are reviewed followed by an extensive outline of the fields of application of the method. Sampling strategies as well as information on individual nuclides are discussed in detail. The power of cosmogenic nuclide methods lies in the number of nuclides available (the radionuclides 10Be, 14C, 26Al, and 36Cl and the stable noble gases 3He and 21Ne), which allows almost every mineral and hence almost every lithology to be analyzed. As a result focus can shift to the geomorphic questions. It is important that obtained exposure ages are carefully scrutinized in the framework of detailed eld studies, including local terrace or moraine stratigraphy and regional morphostratigraphic relationships; as well as in light of independent age constraints.

Trad climber
Los Angeles, CA
Sep 29, 2017 - 07:19pm PT

In this Mercury News article, the climber mentions hammering in a piton in the immediate vicinity of where the rock came loose, and noting that the "Rock seemed loose."

My question for you geologists and geo-physicists is, can pounding one piton contribute to the loosening which led to the rock fall in a significant way?

Trad climber
the middle of CA
Sep 29, 2017 - 07:45pm PT
Drove through today. Crappy phone pic, but for a bit of scale you can see the boot flake (red arrow) and the new scar in this pic.

Ice climber
Sep 29, 2017 - 07:48pm PT
Nice research tuo_trad


The Good Places
Sep 29, 2017 - 07:48pm PT
aspendougy, as a nailer and a rock sciencer, yes.

Trad climber
Leading Edge of North American Plate
Sep 29, 2017 - 08:31pm PT
zBrown: that's Greg Stock's work. I just wanted to pass it on. Anyone who climbs
in Yosemite or is interested in Yosemite geology should be familiar with Greg's work.

For example...
Rockfall triggering by cyclic thermal stressing of exfoliation fractures

Brian D. Collins & Greg M. Stock
Nature Geoscience 9, 395400 (2016) doi:10.1038/ngeo2686
Received 18 September 2015 Accepted 24 February 2016 Published online 28 March 2016

Exfoliation of rock deteriorates cliffs through the formation and
subsequent opening of fractures, which in turn can lead to potentially
hazardous rockfalls. Although a number of mechanisms are known to
trigger rockfalls, many rockfalls occur during periods when likely
triggers such as precipitation, seismic activity and freezing
conditions are absent. It has been suggested that these enigmatic
rockfalls may occur due to solar heating of rock surfaces, which
can cause outward expansion. Here we use data from 3.5 years
of field monitoring of an exfoliating granite cliff in Yosemite
National Park in California, USA, to assess the magnitude and
temporal pattern of thermally induced rock deformation. From
a thermodynamic analysis, we find that daily, seasonal and
annual temperature variations are sufficient to drive cyclic
and cumulative opening of fractures. Application of fracture
theory suggests that these changes can lead to further
fracture propagation and the consequent detachment of rock.
Our data indicate that the warmest times of the day and year
are particularly conducive to triggering rockfalls, and that
cyclic thermal forcing may enhance the efficacy of other,
more typical rockfall triggers.

RE the question posed ^^^ whether a climber pounding a piton could have triggered the
recent rockfall...My $0.02: that slab was ready to go due to multiple natural processes
acting over 1,000s of years before Ryan Sheridan placed that horizontal beak.

Ice climber
Sep 29, 2017 - 08:44pm PT
Nice research Greg. :}

Nice reporting t_t

It does beg the question though if it was 1000 years in the making, why Sept 2017?

Karma? Was that one "pissed off ( or on ) rock?


Trad climber
Leading Edge of North American Plate
Sep 29, 2017 - 09:18pm PT
It does beg the question though if it was 1000 years in the making, why Sept 2017?
The monthly maximum crack aperture plot ^^^ might shed some light on why September?...why 2017? is a more difficult to answer.

Ice climber
Sep 29, 2017 - 09:52pm PT
Very hard for me to read the fine print (may have to go to the source) but June looks kind of suspicious to me. Then, I don't know anything about geology.

It would be interesting to see the data from 2014-2017.


Trad climber
Leading Edge of North American Plate
Sep 29, 2017 - 10:13pm PT
zBrown: I replaced the plot ^^^ with a better image.

EDIT: July, Aug & Sept are the months with the largest difference in daily min/max temps. Also, I think that historical rockfall is evenly distributed throughout the year and that there isn't any seasonal correlation.

Here are a couple of additional plots from the same paper showing diurnal crack expansion and contraction in response to daily min & max temperatures for 10 days in June 2011


Big Wall climber
Ashland, Or
Sep 29, 2017 - 10:50pm PT
It's hard to believe it's a coincidence that Pete's Junk show was hauled through that rock scar the day before it cut loose! Jus sayin...

Trad climber
Cascade Mountains and Monterey Bay
Sep 30, 2017 - 12:00am PT
Claire Mearnz and I were on top of Dolt Tower on the Nose in the early spring of 1985 when a large collection of sizeable boulders fell past us, football sized up to furniture sized.

Several climbs I've done in Yosemite have since had large sections fall off: El Cap Tree Direct (with Frank Sacherer) and North Face of Lower Cathedral Rock (with Layton Kor), and Half Dome NW Face

Be careful out there people

Trad climber
Sep 30, 2017 - 12:08am PT
To the family and friends,

I offer my deepest condolences. I try to think of my daughter or son, wife or husband or friend. I hope you find peace.


Yosemite Valley
Sep 30, 2017 - 05:29am PT
Here are the dimensions and volume of the 28 September 2017 rockfall:

Height: 120 meters (394 feet)
Width: 45 meters (148 feet)
Thickness: Average of 2.5 meters (8 feet), with areas up to 8 meters (26 feet)
Volume: 10,250 cubic meters (nearly 362,000 cubic feet)
Mass: 27,675 metric tons (assuming density of 2,700 kg/m3)

Some of you may be interested to know how these measurements are made. We have baseline high-resolution ground-based lidar data for Yosemite Valley cliffs. During helicopter assessment I'll take hundreds of photos of the cliff as the helicopter moves. These photos are then used to derive a "structure-from-motion" photogrammetry terrain model that can be compared against the baseline lidar data. So the values above are not estimates, they are actual measurements with high precision.

This work its collaborative between the NPS, the US Geological Survey, and the Risk Analysis Group at the University of Lausanne (UNIL), Switzerland.


The state of quantum flux
Sep 30, 2017 - 05:44am PT

The new scar does have an odd whale shape to it.
Delhi Dog

Good Question...
Sep 30, 2017 - 06:36am PT
It's hard to believe it's a coincidence that Pete's Junk show was hauled through that rock scar the day before it cut loose! Jus sayin...

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