Yosemite's Rockfall Hazards and More: A Discussion with Dr. Greg Stock, Yosemite NP Geologist

[@shawnwillsey]

Please be sure to LIKE and SUBSCRIBE. You can support my educational videos by clicking on the "Thanks" button just above (right of Like button) or by going here: www.paypal.com/donate/?hosted_button_id=EWUSLG3GBS5W8 Or: www.buymeacoffee.com/shawnwillsey

[@RWBHere]

That Lyle Glacier retreat is both dramatic and depressing. Thank-you both for this interesting discussion and explanation. 🙂👍

[@richardwest9054]

Shawn, your discussions with Nick Zentner, Myron Cook and, now, Greg Stock have greatly expanded your repertoire. P{lease keep them going, and don't let up on your earthquake/eruption updates and the Random Roadside Cuts.

[@marksinger3067]

Hello Shawn and Greg.. Old Californian here explored Yosemite before bear proof trash cans..Worked for Curry summer 1976 did most of the standard hikes.. Love Snow Creek waterfall..Have friends in Twain Harte and Sonora and remember Murphys..It's perfect that they found a geologist from the area..

[@cindy8426]

Thank you so much Greg and Shawn! I never knew!!! I learn something new everyday. I wish I had known back in my school days how much I would enjoy geology! Thanks again!

[@fhedrick5019]

Special thanks to Greg---Shawn, it would be fascinating to hear from some of the other National Park geologists if possible-thanks for the effort you put into these videos

[@Whtwngd]

True, I enjoyed every topic covered in this video. Very entertaining and I still learned something new. I’m 73 and been to this park 4 times (camping and minor trails) so I am tickled pink hearing the special background on the rocks and such. I also didn’t know there are so many rock slides. I’ve watched many a documentary-thank KZbin- about climbers going up the granite walls. They make on like the granite isn’t going anywhere. Well now I know the truth and I think the climbers are out of their minds! Great idea for a Park geologist to do a similar show like this one. Of course the interview questions kept things rolling. Great job to both of you.

[@jrepka01]

Great interview! I haven't met Greg, but I also went to graduate school at UC Santa Cruz in geomorphology. We even worked under the same advisor but I finished just before he came on board. Also, how great to get to be a co-author with the great Clyde Wahrhaftig, my first geology idol. One of the great field geologists who was also a big advocate for public transportation, he created many geologic field trips around the bay area that were all accessible by bus or tramway, and was an early advocate (1960s) for recruiting under represented groups into geosciences...

[@priestessaranel]

I'm a GIS specialist for Mono County (right next door to Yosemite), and I think a pretty simple aspect analysis could be applied to whatever elevation model you used to map the historical rockfall locations (of course something super-high-resolution like Lidar would be better, but even a 10m DEM would work). By overlaying the points on top of the aspect map, you could then assign an aspect to each rockfall point for further frequency analysis. Hope that helps!

[@GeistView]

On my channel I have a few drone videos done in Tioga pass. Some of the shots when flying over rock formations you can see the Glacier Scour marks left over from the last glacial events.

[@LizWCraftAdd1ct]

Now I know why I avoid rock climbing. Very interesting to hear a geologists perspective on the national park. Thank you both.

[@Steviepinhead]

Another sweet entry in this awesome interview series.

[@lisadyck9503]

Thank you for this fascinating interview.

[@JudithDickson-b8c]

Thanks for this great presentation!!!

[@joannekellam191]

Thanks for conducting and sharing this great interview! Interesting perspective. I am sure that folks like Greg appreciate being interviewed by a knowledgeable colleague and you do a great job.

[@KnucklebarkRanch]

Yea as time goes on we get intelligent field geologist to show and tell us about building in areas of present dangers of huge rock falls and slides by examining those of the past in ancient time and of moderns times. Great job guys and very informative thank you .

[@jimruddy6083]

I had no idea that rock falls were so prevalent there! kudos to Dr. Stock and the staff at Yosemite who have the challenge of allowing people on the trails while working to minimize the danger to them. Sounds like very interesting geology mixture for a college professor to analyze and share. Road trip?

[@dlane5292]

Years ago my family had a cabin near Quincy. Lots of rock slides thru the Feather River Canyon especially in the Spring.

[@jmuehlbauer42]

Thank you for the interviews! I ride down to Saint Paul once a month for MN Quilt meetings. Along the way we pick up a woman who is a retired geology professor. I can ask her one small question and I know I will get an indepth answer that may be a half our long. Her passion for the earth , like yours, is without limits. Keep up the excellent work, Shawn, you and your guests knowledge is fascinating and I always appreciate learning something new! Cheers!

[@johnjunge6989]

This was great. Having just been in the area last year, from Illinois, I wouldn't have guess how active the Rock falls and various movements are. Greg, thanks for your insight as to what's going on around Yellowstone. As a novice geologist, I find your job really interesting. 😊

[@darwinboor1300]

Thanks Greg and Shawn. Love visiting Yosemite and Mono Lake. Several great circle drives from the west. A regular on the inland version of our west coast passage from Seattle to SC.

[@raenbow66]

Having hiked in Yosemite a couple years ago, this talk was really relevant. Very interesting! Much appreciated, Greg and Shawn.

[@StarBitt97]

That was such great information! I have been to Yosemite several times and this interview was so interesting to me. Thanks Shawn!

[@user-ic6vy2ii9m]

Thank you both! What a very nice talk, I enjoyed listening a lot and will come visit as soon as I can :) Greetings from Europe

[@maryt2887]

This was a fascinating discussion of one of my favorite places. Although I was in Yosemite only twice, I would love to return and now I know so much more about its formation and ongoing evolution. Thank you Greg and Shawn for providing this opportunity! Looking forward to more discussions.

[@dancooper8551]

Fantastic interview! I would kill to have Greg’s job. Spent a lot of time in Yosemite and hiking around previous rockfalls was fascinating. The damage done by pressure wave blasts from large rockfalls is incredible. Thanks!

[@susiesue3141]

Thanks for sharing! Very interesting! 😊

[@marymachunis3778]

This is so fascinating! Thank you Shawn and Greg.

[@sandrine.t]

Thank you @shawnwillsey and thank you Greg Stock! Such an informative and enjoyable conversation between you two :) Now I must visit Yosemite National Park! (my bucket list keeps getting longer and longer ;)

[@marksinger3067]

Shorten that list and put Yosemite at the top especially the high country Tuolumne Meadows..It will enhance your soul..

[@johntrotter8678]

As our "neighborhood" National Park, this Yosemite background was fascinating. I will look at the walls differently now. Thanks.

[@GailVaught]

Never visited Yosemite when I lived out west and now I wish I had. Fascinating to learn about all the rock falls. Thanks for interviewing Greg, which, BTW, is a great name since it is my brothers name.

[@loopbraider]

Wow thanks for this interesting interview, both Drs Willsey and Stock! Really interesting to hear about Greg Stock's work and expertise in Yosemite and see all the amazing photos. That is so cool that Dr. Stock finished Clyde Wahrhaftig's big Yosemite project! He was such an icon of a CA geologist, and an artist too did beautiful field sketches. Plus a great writer, readable and witty. I love his Streetcar to Subduction booklet on geology daytrips in the sf bay area.

[@anitapaulsen3282]

I learned so much about Yosemite! This was fascinating. Thank you both!

[@jamesdubben3687]

Thanks for the great discussion.

[@3xHermes]

Thanks Shawn and Greg. Great video

[@cdineaglecollapsecenter4672]

Great conversation! Love Yosemite.

[@y3ssydo]

Amazing stuff to learn. Thanks for sharing.

[@CricketsMa]

Thank you Gregg and Shawn! This was riveting. I never would have guessed there were so many rock falls! Granite national park is a great description. Sorry to see the glaciers getting so small. I would love to know more about how one studies and anticipates rock falls.

[@EddieSchirmer]

here in Vermont, not too long ago, within the last 2 or 3 years, there was a Massive boulder that fell onto a road surface and hit an, thankfully unoccupied car on Smugglers Notch. it took a Dozer to move it, and i think they had to blast it into a couple pieces even then. it just goes to show that even here in Vermont, there are rock fall hazards which most people are unaware of. and, it also goes to show, that even this Ancient and glaciated landscape has hazards still. i know of a land slide near me, near Sugarbush Resort, that apparently is a slow creep feature, though i haven't read up on it so i dont know if it is named or what the name may be as such. BUT, i have shallow bedrock and outcrops around my house, and there is even a Massive boulder which was carved into by the settlers and residents int he 1800s where they put a corner of their workshop on. its definitely something to think about, how the landscape was shaped over time, and how that affects the current state of its use and hazards.

[@DaveBartholomew-uf6sm]

Great interview. I am going to pass this link onto a good friend who lives just outside the park and spends lots of time up there.

[@bryancurry1898]

Thank you for this excellent interview. This discussion of rockfall reminds me of a Grand Canyon hike a number of years ago. We were on our way out the Boucher trail. Traversing on top of the Redwall, we came upon a slab of rock the size of a ranch style house, sitting on top of the trail. Someone had scratched “I saw this rock fall.” and a date two days before the date we saw it. It would take some nerve to walk up to that rock and write on it, but he must have needed to climb around to get out to the trailhead, as did we. Erosion in action!

[@dougsundseth6904]

Interesting interview; thank you. Last fall I spent probably half an hour speaking with an NPS geologist at Valles Caldera National Preserve. IIRC, he was also responsible for Bandelier NM. It's a geologically fascinating area (volcanically active from Great Sand Dunes down to Los Alamos, mostly), and I suspect he would make for an excellent interview.

[@scottadamson8836]

No pun intended, but you hit this video out of the park! Both you and Dr. Stark did a wonderful presentation. More if these videos.on occasion please.

[@runninonempty820]

I had no idea that Yosemite had so many rock falls. I HAVE to get there one of these years!

[@phyllissmith1105]

We used to live near Yosemite and went into the valley quite often for picnics. We heard a rock fall across the valley from us one time when we were there. It was kind of scary.

[@jeannewells6747]

This was great 🤗

[@wpherigo1]

Nice work, gentlemen!

[@MyMemphisable]

Thanks!

[@marcialoofboro306]

Very interesting!

[@ellenperrin629]

So interesting processes!

[@laudas11]

Super 😊

[@davidk7324]

Gravity. Thanks for this, it reveals a number of dynamic processes that we rarely see in action. The road rock falls remind me of the Banks-Lowman road in Idaho.

[@YOICHIHAGIWARA]

ありがとうございます！

[@dlane5292]

Anyone watch that Free Solo Documentary featuring American Rock Climber Alex Honnold climbing up El Capitan? Fascinating but crazy stuff!

[@KSparks80]

That dude is from some other planet! Free climbing several thousand feet straight up just isn't human. lol Unreal stuff!

[@TheLawDawg]

Well done Greg. All those days we spent caving paid off. 😁

[@Joe-Skier]

Nice reminder of any time you venture into the back country, you're not completely in control of what can happen regardless of your back country experience.

[@vickihubach4388]

I love those metamorphic rocks at May Lake! I think... you may have said... if I remember correctly, that those sediments originated from where the Mojave desert is today(?) Anyway, I read your book, Greg, and attended one of your outdoor talks (with the Mono Lake Chataqua bird festival). My son was a wilderness ranger in Yosemite for 8 years, but is now pursuing graduate studies in GIS. Got any good projects he could help work on for his thesis? :)

[@BarbaraJustme]

I'm only 20 years away from a century, and my dad took us to Yosemite often since I was born and raised in CA. I seen El Capitan before rock climbers took over that rock and I swear the damage to El Capitan has been caused by the ro k climbers more than earthquaskes!

[@dlane5292]

Thats expansion rock looks about 50'x 18', & probably 140,000lbs. Wowzers!

[@madcolor]

Great video. Was just up there. Im wondering if anyone has the link to Dr. Greg's rockfall interactive data?

[@marksinger3067]

Just a question..what kinds of geology is done in the Yosemite High County, Tuolumne Meadows area where rockfalls are fewer..

[@bottomup12]

As they do for avalanches, should a canon be shot at loose ares to force a rockfall? Or would that just make more fracturing?

[@JackMenendez]

Hi Shawn and Greg, thanks for this beautiful video. Shawn, I've been watching your videos for a while now. Thank you for them. I have a question about thermal stress on exfoliation slabs. Before going on, let me say I am a software engineer who started alpine climbing in the high Sierra during the mid-60s, and I was a rock climber in the valley from 1969 through 1996. Man, I have seen some changes; I remember glaciers that no longer exist. I climbed the Lyell glacier at 50% of the 1883 picture. We could drive to the Cookie Cliff and belay from the driver's seat. In fact, we often snuck in and out of the valley without paying by driving down the Old Big Oak Flat Road, scary in a 1960 Ford Falcon. It cost me $1.25 a day to live in Yosemite. So, I asked a Geologist about thermal stress on exfoliation slabs back in the 1990s, and he totally scoffed at me, "No, it has nothing to do with rockfall blah blah blah." This geologist had written a newspaper article about the dangers of rockfall in Yosemite. Well, I am glad to hear that thermal stress is being studied. The anecdote I told that Geologist is the famous Hourglass slab. We would hammer pins into the wide cracks and not remove them because we couldn't get them out. The rock expanded that fast. But we could return the next day, and all the pins would lie on the ground at the bottom; our pins and booty gear, too! You partially answered my question, but I would like to know if thermal stress can initiate exfoliation and if climate change accelerates exfoliation. I say that because of the rockfall that happened in the 70s at El Cap Tree which is to the right of the North American Wall. It´s a long story, but it seemed like an exfoliation slab suddenly appeared at the end of a very hot day on a smooth wall while climbers were on it. They actually watched the crack form right in front of them. The process ceased during the night, but the next day was hot, and that was when all hell broke loose. I also wonder if terrestrial geologists are taking lessons from what we see on Mars and the thermal stress on rocks there, which is many times that on the Earth.

[@KSparks80]

I'd think that very short differences, such as day/nite temp changes and winter freeze-thaw cycles would have much more effect than a long term change in the climate. And even with long term climate changes supposedly warming the planet, you'd still have the same day/nite temp changes, but less of the freeze/thaw changes. Seems that would cause less exfoliation/rock falls, not increase it. Freezing moisture in/behind a rock is a powerful way to bust it up.Expanding ice does not liked to be trapped. lol

[@JackMenendez]

@@KSparks80 Except that the short differences make considerable changes in the thickness of a 350-foot-tall slab that is 20 feet thick. That was the point of the Hourglass story. The thickness changes noticeably from hour to hour. It's like Yosemite Valley breathes. I wish I could post a picture, but you can see them on Mountain Project.

[@loopbraider]

I recently read an article somewhere (National Geographic or something similar) on a study on daytime summer heat causing exfoliation, including a link to a video of exactly what you described - a small exfoliation slab suddenly detaching from the one beneath it with a "pop" and visibly kind of hopping up a few millimeters as it cracked. Daytime and warm, no freezing involved. So it's now pretty accepted that heat can cause this as well as - or maybe even more often than - freezing. Wasn't known (by geologists) to be a thing back in the '90's I guess.

[@JackMenendez]

@@loopbraider Thank you for this.

[@KSparks80]

Wow. If that "Boot Flake" is still on El Cap, it sure looks like it's a short timer! lol If they feel it's needed, is the Park Service allowed to remove the flake if it's deemed a hazard? Or do rules require things to happen "naturally"?

[@saimaleon7115]

Yosemite gives me the creeps. From the valley I look up and see that half a mountain just suddenly slipped down and is strewn around the valley. Then I look up and around at the other mountains and see smaller sheared off areas and think “any time now”. Since I’ve lived in CA there have been rockfalls and one killed two Yosemite workers. So I just can’t do Yosemite any more.

[@professorsogol5824]

Do you drive your car? Searching around on the internet, I learned there were 39 traffic-related fatalities in San Francisoo in 2022. Contrast that with 9 fatalities in Yosemite National Park from all causes - traffic, wildlife, rockfall, homicide etc in 2021. You would probably safer in Yosemite than walking around your home city.

[@briane173]

13:45 "Pics or it didn't happen." 🤣🤣

[@merryhunt9153]

I followed you about the release of compressive stress, but you lost me on the tensile stress. What is that exactly? What causes it? 2. About that Boot Flake. How big is it? (for a while I thought the climber was a dead leaf and the Flake was about 24 inches long.) Where is it? Is that a high cliff on the left or a mere step down in the granite?

[@richarddavies7419]

As to stresses- a chunk of rock supported near one end and sticking out and trying to bend a bit will have compression on the lower side (below the neutral axis) and tension on the upper side. Added to those stresses will be shear across the cross section at the bending point. Stresses in a three dimensional body are also three dimensional (triaxial). Added to all of that there could be torsional stresses, adding compression, tension, and shear stresses. That is just with the weight of the chunk; there could be stresses induced by adjacent chunks in contact with the original thing being discussed!

[@KSparks80]

A way to visualize it is to picture a layer of rock being folded into an upside down 'U" shape. The rock along the bend on the inside edge of the U is being squished together, or "compressed". The rock along the bend on the outside edge of the U is being stretched, or placed into "tension". It's being pulled apart. Hope that helps a bit.

[@professorsogol5824]

Boot flake is pitch 17 (out of 34, so about half way) on the Nose of El Capitan. El Captain at the Nose is about 880 meters tall, so that would put Boot Flake at about 440 meters from the ground. Assuming the figure on the right side of Boot Flake is of average height, I estimate the flake is about 10 meters tall.

[@muzikhed]

Is that apicture on the wall behind Greg or is that really a Milkyway night sky view ???

[@shawnwillsey]

Computer effect to obscure background.

[@Riverguide33]

👍

[@lectrikdog]

frost/thaw fracturing

[@dlane5292]

My wife, & I visited the park in 2016. Was very beautiful as expected, but usable facilities access for those with disabilities was shamefull. Some of PR's were of less then desirable attitudes, & mannerisms too. Hopefully that situation has gotten better since then...

[@StereoSpace]

30:13 Geotechnical engineer David Rogers tells a story of a rock slide in the Sierras that took out a firehouse and killed everyone inside. Not 200 people living in that whole valley, how did you manage to kill all the fireman? By building the firehouse on a bench left from a previous rock slide, that's how.

[@allenra530]

Background event frequency is something that many people do not seem to understand. I live close to Yellowstone and the background level for earthquake events is several hundred per month. About half of the tremor events occur in swarms, sometimes more than 1000 events in a swarm, sometimes less than 100. There are alarmists who seem to think that any swarm that occurs is a signal of an imminent eruption and anyone who disagrees with them is a government shill who is participating in a coverup "to avoid panic." It doesn't seem to matter to them that they are proven wrong every time, just by the fact that no eruption happens. The next time a swarm happens, they come right back with predictions of disaster. I suspect that they are adrenaline junkies who are addicted to anxiety producing predictions. Occasionally, Mike Poland and his predecessor have had to issue statements refuting the wilder predictions. One video clip of the now retired Park Geologist, from the Ask a Ranger series, was used for years to support the predictions. Even after Hank transferred to another park and then retired, they were still putting his video clip in their prediction videos as if he had just made it. This particular headache may be confined to Yellowstone, due to the scale of destruction that a large eruption can cause.