Rock fall off p2 City Park

[rob]

I'm not saying it wasn't trundled. I don't know. I'm just saying it is ridiculous to start assuming motivation behind the supposed trundling.

 

Perhaps it was trundled for fun? It probably made a pretty satisfying boom. Perhaps it was trundled because the guy was trying to make it land on his ex-wife. Perhaps it wasn't trundled at all. WHO FUCKING KNOWS. I'm curious why you seem so certain it was trundled to make the route safer? Know what I mean?

 

Personally, it sounds like a lot of fap-fap-fapping. "No, it needs to be moved 9.75 inches to topple, not 6.3!" etc. etc. Are you guys kidding?

 

 

 

[G-spotter]

30 years of engineering background,

 

You sound like you need to look for some refresher hours, here's a good link

 

http://books.google.ca/books?id=yF0IeLRKjDMC&pg=PA200&lpg=PA200&dq=block+topple&source=bl&ots=2PXTV-Qsxf&sig=f72mO0lhxkoYokJWlZCFdNcoBqQ&hl=en&ei=uoToS5qbIIj-tQOLyOnJBw&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCMQ6AEwAg#v=onepage&q=block%20topple&f=false

[Buckaroo]

Okay Tvash, I've lost you on the cause of the rockfall.

 

But IF this was trundling would you say right or wrong?

 

Would you say that depends on whether this was a "death" block or not? I would say so, yes if it was about to fall then knock if off.

 

What if it was not about to fall and it was trundled, what would you say?

[tvashtarkatena]

Engineering backgrounds aside (I got me one a those, too, but you can't swing a dead LOLcat here without hitting one...but they're mostly software geeks so they don't count), it's my experience in stone masonry that seems more relevant. 3 points of well positioned contact is all you need for a stable block. One of the points can be a pebble, grain of sand or stick. Alter one of those supports a little bit (impossible!) and stability can be gone, just like that.

 

Speaking from my massive and decisive engineering background...I would never make such a proclamation about such a system without any knowledge of the system before failure. It's just not, you know, good engineering. That, and the fact that there are lebenty leben trillion tons of constantly exfoliating rock hanging over the thing.

 

What is it about this blame fetish? Fkn weird.

Edited May 10, 2010 by tvashtarkatena

[tvashtarkatena]

If I were climbing the route, and pulled on the block, and it moved and I felt it presented a hazard to future climbers, and the coast was clear below...bombs away! Better to step on a few sensitive toes than to see some poor younguns kilt before they've gone forth to make their mark!

 

 

[Buckaroo]

Nice link Dru. There's drawings of toppling rocks, but I don't see flat ledges, only angled ones.

 

 

you mention vegetation, dirt and water moving rock.

 

we can rule out vegetation as in tree roots which do move rock because the dirt was 3' down in the crack.

 

So describe to us Dru the exact mechanics of dirt and water moving rock.

[Buckaroo]

You're right Tvash, I've gone further than my cursory exam of the scene justifies. I'll look closer and get back with you guys.

 

It's only my passion for the area that makes me be this way.

[MarkMcJizzy]

You guys are fucked up. You don't even know that it was sitting on rock. Looking at the photograph, it appears to be sitting on a dense bed of dirt and roots.

 

And if it was trundled, was it because it was loose? Or for fun? It would be wrong to trundle it for fun or to prevent a ledge fall, but if it was suddenly loose, that would be reasonable.

 

And we have no proof that it was trundled except for some rumors and some questionable forensic geo-engineering

[G-spotter]

Nice link Dru. There's drawings of toppling rocks, but I don't see flat ledges, only angled ones.

 

 

you mention vegetation, dirt and water moving rock.

 

we can rule out vegetation as in tree roots which do move rock because the dirt was 3' down in the crack.

 

So describe to us Dru the exact mechanics of dirt and water moving rock.

 

1) vegetation cannot be ruled out because you don't know what moss, dead wood etc was down the crack out of sight

 

2) clay minerals are a secondary product of feldspar weathering; feldspar is a major component of granites; many clay minerals shrink and swell when wetted as does dead wood, while living wood (roots etc.) continuously increases in size and provides progressivbe pressure over time.

 

3) dirt and water in cracks both lubricate and increase capillary pressure making for drastically reduced friction and increased driving force to failure

 

4) pressure differential front/back of block from gust eddying along cliff face (rotors) during the severe windstorm last week by itself probably would not cause blockfall but when combined with intense convective precipitation providing water for mechanisms 1-3 above, is a plausible failure mechanism.

[G-spotter]

Another reasonable cause would be, as Mark mentions, dead roots in the base crack over time, progressively decaying and reducing root cohesion, resulting in progressive long term loss of strength.

[Buckaroo]

"many clay minerals shrink and swell when wetted"

 

producing pressure like ice or just bulging out the sides?

 

""while living wood (roots etc.) continuously increases in size and provides progressivbe pressure over time.""

 

any trees within root distance of the crack in the photos? roots have to contact the rock on both sides to cause pressure, not just their presence in the dirt

 

"" dirt and water in cracks both lubricate and increase capillary pressure making for drastically reduced friction and increased driving force to failure""

 

Looks like a fresh rock scar, not much dirt on the flat ledge. Although that is uncertain where the fresh dirt has been spilled.

 

What kind of friction coefficient lubricated by dirty water do you need for a flat bottomed block to slide off a flat ledge?

 

""4) pressure differential front/back of block from gust eddying along cliff face""

 

maybe a huge thin flake that was already teetering

 

""dead roots in the base crack over time, progressively decaying and reducing root cohesion, resulting in progressive long term loss of strength.""

 

The nearest "tree" is a 2' bush 15 feet away. Large live tree roots can push rock out, like something a few inches in diameter. The overhang on the outside edge is 1" to 2" so the live root would have to be at least that big. I see a small root less than 1/4" dia in the pik. And dead roots would have no effect, this block wasn't held on by roots.

_________________________

[MarkMcJizzy]

I think Dru has given a very plausable scenerio. If it was trundled, it was likely that it was because it suddenly became loose or wobbly. At which point common sense would dictate that it should be heaved away.

 

I seriously doubt that a jack was needed. A good digging bar would do it no problem

[Sol]

Yeah darin, someone was climbing that block on The Golden Road when it launched.

 

The block we saw spontaneously drop on the UTW was about the size of a volkswagon golf and was sitting on a flat ledge. It didn't topple over, more like slid out of the wall (gravity defying), then dropped 50 of so feet to the ground, broke into a bunch of pieces, that went catapulting down the hill for what seemed like forever.

 

Then there's those blocks that came off Orc Tower last year, that block on Steel Monkey.... Really man, i'd say of all the places in WA state to have spontaneous and unexplained rockfall its Index.

 

Luckily for all of us, Buckaroo is on the case and will use his 30 years of engineering experieince to get to the bottom of this blatant and premeditated case of unexplained rockfall. I'm going climbing.

 

PDXers never-mind, just as ridiculous up here.

[Peter_Puget]

One thing we all can agree on is that the "perp's" biggest crime is not cleaning off the ledge! Certainly after jacking off a stupenduo :ous trundle they could have at least brushed off the ledge!

[marc_leclerc]

When I free soloed City Park's first pitch my focus was so extreme that I momentarily had mind powers that launched the block into space. For this I am truly sorry.

[rocketparrotlet]

Is the ledge in question the belay ledge at the top of Godzilla/City Park p1 or is it something different?

[turn_one]

Yeah darin, someone was climbing that block on The Golden Road when it launched.

 

The block we saw spontaneously drop on the UTW was about the size of a volkswagon golf and was sitting on a flat ledge. It didn't topple over, more like slid out of the wall (gravity defying), then dropped 50 of so feet to the ground, broke into a bunch of pieces, that went catapulting down the hill for what seemed like forever.

 

Saw the evidence of this on Saturday. There's a good size block (new) sitting right in the middle of the UTW trail you have to climb over/around it...about 25' past the block is a victim of the rockfall, a 2' + diameter fir laying across the trail. Went to the base of Golden Road to investigate, block definately seemed to originate from this area...pretty powerful stuff.

[MarkMcJizzy]

Back in the old days, when paranoia ruled CC, some moderators would have preferred us to refer to " the large bl*ck that s*meone tr*n***** off City P***", just incase the NSA was monitoring this frequency

[cbcbd]

When I free soloed City Park's first pitch my focus was so extreme that I momentarily had mind powers that launched the block into space. For this I am truly sorry.

 

freakin kids

[el jefe]

PDXers never-mind, just as ridiculous up here.

 

with five pages on this subject thus far and no end in sight, i'd have to say you guys have taken the lead as far as loony obsessions go. we're going to have to start trying harder...

[boadman]

"many clay minerals shrink and swell when wetted"

 

producing pressure like ice or just bulging out the sides?

 

""while living wood (roots etc.) continuously increases in size and provides progressivbe pressure over time.""

 

any trees within root distance of the crack in the photos? roots have to contact the rock on both sides to cause pressure, not just their presence in the dirt

 

"" dirt and water in cracks both lubricate and increase capillary pressure making for drastically reduced friction and increased driving force to failure""

 

Looks like a fresh rock scar, not much dirt on the flat ledge. Although that is uncertain where the fresh dirt has been spilled.

 

What kind of friction coefficient lubricated by dirty water do you need for a flat bottomed block to slide off a flat ledge?

 

""4) pressure differential front/back of block from gust eddying along cliff face""

 

maybe a huge thin flake that was already teetering

 

""dead roots in the base crack over time, progressively decaying and reducing root cohesion, resulting in progressive long term loss of strength.""

 

The nearest "tree" is a 2' bush 15 feet away. Large live tree roots can push rock out, like something a few inches in diameter. The overhang on the outside edge is 1" to 2" so the live root would have to be at least that big. I see a small root less than 1/4" dia in the pik. And dead roots would have no effect, this block wasn't held on by roots.

_________________________

 

Anybody considered vibrations from a big freight train? I'm always freaked out when I'm on lead and one thunders by. It definitely makes some of the bigger flakes vibrate (i.e. sagitarius/jap gardens). If one of the corners was supported by some sort of pebble, I could see it rocking loose.

[summitchaserCJB]

This thread is over the edge. I'm too bored to read it.

[G-spotter]

well shit go back to arguing over whether thinfingers is 10d+ or 11a- then

[summitchaserCJB]

I mean cmon...it's a block. I don't see anyone hoisting it back up there.

[tvashtarkatena]

Passion's cool, but when it gets to the point of trying to figure out who caused AIDS, the Virgin Birth, and the Asteroid that Killed the Dinosaurs, it can seem a bit over the top.

 

I hope this kind of passion doesn't extend to the alpine, cuz I've witnessed a lot of spontaneous rockfall there...as in me finding a nice big juicy block and spontaneously deciding to give it a friendly nudge.