Massive rockfall - Waterfall route


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Dec 6, 2017 - 10:37pm PT
What I was getting at without saying it is that the majority of root growth occurs- mid summer.

Not so; and especially not so in the Mediterranean climate (wet in the cold season, dry in the warm season) of California. Roots aren't the culprit in Yosemite rockfalls (or hardly any others, either).

c wilmot

Dec 7, 2017 - 05:52am PT
You are right tLp- nothing grows mid summer in ca. Everyone knows Yosemite turns green during its lush winter. Realy- it's the ideal light cycle the mid winter months provide that really gets vegetation growing.
And thank you for you tireless research proving that no Yosemite rockfall has ever been caused by root growth

Dingus Milktoast

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


Boulder climber
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.


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

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.

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
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?
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