[et-al]

Like you said, it's not uncommon for people's feet to slip out from under them. A big part of climbing is the friction your shoes have against the rock, but move around, reach for something, and angle of your foot against the rock changes, along with the friction, and zoosh: your foot slides off.

The rock can break off ("chossy" climbs, Pinnacles is notorious for this), but that's a less common occurrence than Hollywood would lead one to believe.

[Baeocystin]

>The rock can break off ("chossy" climbs, Pinnacles is notorious for this)

A doctor from our local hospital died from, as far as we can tell, exactly this while climbing Discovery Wall. He was an excellent climber, and was using appropriate gear. He just was in the wrong place at the wrong time, and his safety equipment wasn't enough.

[2muchcoffeeman]

Depends on the rock. The sandstone along Sydney's eastern beaches can be fragile in places.

[petertodd]

El Capitan is granite, and perhaps even more importantly, it's very heavily climbed so for the most part anything that can break will have already been broken off by someone else.

[hluska]

I don't agree with that. In fact, I wear a helmet whenever I am near a wall because I have seen way too many formerly solid looking rocks fall, even on granite.

Heck, a few years ago, a 2000 ton slab of rock fell off of Half Dome, which is a famous granite dome in Yosemite. I can't find the article now (of course), but I read a great article about how rock expands and contracts with the heat of the sun, water gets into cracks and plates will break off.

This article is okay, though it isn't the one that I'm thinking of. If I can the correct article, I'll edit this answer.

http://www.livescience.com/51490-yosemite-half-dome-rock-fal...

[petertodd]

You're missing a very important distinction though: for a solo climber the main thing out of their control that's different from normal rock climbing is holds breaking unexpectedly. For that risk, having lots of people climbing the rock helps increase the chances that such unexpectedly weak holds will have been broken already by someone else; obviously loose rock isn't so much of an issue, for the simple reason that you know it's loose and can climb appropriately.

Rock fall meanwhile is dangerous to all climbers, whether or not they're using ropes. Sure, it's more dangerous to a solo climber - you might get lucky and just get knocked out, something a rope can save you from - but we're talking about a moderate risk vs. high risk comparison, not zero-risk to high risk. That 2000 ton slab you gave isn't a very good example, because something that big has a pretty good chance of killing you rope or not.

FWIW, I do a lot of cave exploration, and in caves the "already broken off" effect is a very powerful one. Virgin passage that's never been explored before can be a very scary place to be because everything can be loose and ready to fall. This is particularly true in areas that undergo freeze-thaw cycles, such as upper parts of alpine caves - I've been in places where every single bit of rock, including the ceiling, is heavily fractured due to frost. Breakdown piles are also a big problem - they're huge piles of rocks and boulders, generally due to ceilings gradually collapsing, and you have to be really careful around ones that haven't been visited frequently because pretty much anything you stand on could be unstable. Lots of cavers have been trapped in breakdown piles that shifted unexpectedly.

The underlying cause of this problem in caves is simple: caves can be very static environments with no weather, increasing the chances that the force you exert on a rock will be the largest force it has ever experienced in that position.

[idlewords]

This is an exceptionally interesting comment. Thank you!

It occurs to me that this phenomenon will also be a big risk factor in lunar exploration, if people ever go back up there.

[petertodd]

Thanks!

Oh, is http://idlewords.com/2007/04/the_alameda_weehawken_burrito_t... yours? That's basically my favorite blog post ever.

[eagletusk]

Or someone can drop gear.

10% of El Cap accidents are falling objects http://www.climbingyosemite.com/portfolio/danger-zones-nose/

[2muchcoffeeman]

Yeah, I'm just saying the things that go wrong depends on where you're climbing.

[petertodd]

Yup, you're 100% correct there.

For example, I've personally done quite a bit of what's actually free soloing in cave exploration, but that style of climbing is done in confined spaces with rock on every side. You're much less dependent on individual holds as you'll usually be supporting yourself by pushing against the rock with your whole body, so it's a lot safer than most free soloing - even if you do fall you have a good chance of self arresting by, and if you can't you can at least slow your fall significantly and just slide to the bottom.

[jonah]

In the Outside article up thread, Tommy Caldwell who free climbed the route with Alex a couple weeks ago mentions loose rock as scaring him: "I went to Yosemite last week over the Memorial Day holiday and we did a practice lap on the Freerider with a rope. High on the wall, panting and sweating, feet smearing on crispy flakes that made crunching noises as I stepped on them."

[et-al]

Yeah, sandstone and water don't mix.

I was highlighting the sudden surprises that tend to catch a climber off-guard. If someone is climbing on wet sandstone, they should already be cognisant that it may crumble. (They should also avoid climbing it when wet so that they don't break holds, but that's another topic on stewardship.)