Yosemite's Greatest Hazard Lurks Above The Valley Floor 

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Park geologist sounds like a dream job.

I was in Yosemite almost 70 years ago. I really enjoyed this video!

Lived there for five years and was there for that fall. It was something else. Thunder still causes me to look up and nearly run 😂. Miss yosemite like crazy though. ❤

Experienced an awesome earthquake in immigrant basin just north of here in the late 1970s. Fully moonlit around midnight. Suddenly the birds started squawking and unseen animals could be heard running through the wooded areas. My little bro's saucer sized eyes clearly visible, the hair on my arms was standing on end. And then the trees swayed violently. Kibbie Lake began to slosh south to north and back. Bang!, Bang!, Bang! slabs of polish snapped loose and slid down into the upset water. After that, I stopped putting things on my bucket list. Every time I try to think of something to right down, it pales in comparison to these five minutes of absolute wonder!

Was in Yosemite during a rock fall. The sound is incredible, we werent close to the source but initially had no idea what it was. Some people thought is was gunfire!

First time in Yosemite was 1960 when 10yrs old..No Bear-proof trash cans then and they roamed around everywhere..Worked there when 27 for six months..Camped many times since then all over the Park..Last time was 2018..Hope to go again.. John Muir during a huge earthquake just marveled at the rock walls falling all around him..Special fellow..

I worked at Happy Isles when the big one happened back in the 90's. The only reason we survived is we closed up early to have a bbq. The slide happened as we drove away on the service road.

I've been to a lot of National Parks, and when I finally add Yosemite to the list, I'm going to remember this video quite well. Thank you Shawn, for all you do.

Yosemite is a great place to talk about batholiths, plutons and varieties of granitoids. There are at least 5 distinct varieties there.

Great video as usual. I always look forward to your videos.

I was working in Yosemite in May of 1982(as I recall) doing observations on a peregrine falcon eyrie on the north American wall. We were doing egg manipulations and the climb was sketchy so we wanted the timing right. That was when an earthquake touched off in Coalinga. I don't remember feeling the quake but I do remember seeing what looked like smoke but was actually simultaneous rock falls all over the valley. Being at my observation point in the rocks directly at the base of El Capitan it was surreal. I didn't know but surmised what had happened. It was not until I got back to my office at UC Santa Cruz and saw the big boulders that had broken loose and rolled into the lower quarry just how significant it was. Oddly enough I was at my office when loma Prieta touched off , that was one of my more memorable events.

It’s fascinating to realise that what we see now has been on a spectacular journey.

The sound of that rock fall must've been mind-boggling.

I laugh at myself when I realize that I like rocks. So I'm glad to watch your video to the end. I also like to watch landslide videos. This is everywhere on the planet. especiallychinaha

Absolutely fantastic explanation of the minerology , plate tectonics ,and glaciation events here professor. Got to be careful for possible erosion activity that can ruin one's day.

I’ve visited Yosemite a couple of times when my son lived in California. It’s so beautiful and varied. The light on the rocks and the shapes of the mountains and boulders is fascinating. I pulled up my photos from my visits there and had a nice reminiscence.

The first time I went to Yosemite, I hiked the mist trail. I remember coming to a clearing in the trees where there was a switchback and a rock face. I looked up and there was a vertical drop of about 2000 ft about 6 feet away from me. It was very alarming on an instinctual level and I felt like I stumbled into a shooting gallery that could pop off at any second. It freaked me out.

The rockfall event that stands out in my mind is the July 1996 Happy Isles, YNP example. I was assigned to the Incident Management Team (IMT) managing the New Years 1997 flood recovery some six months later. While on that assignment I met the NP Law Enforcement Officer (LEO) who was first on scene. His description was a huge slab of granite (I don't remember the dimensions) released very high and simultaneously or within moments separated into two, unequal, sized slabs. The larger slab "got big air" on the way down and landed flat- like dropping a big book down flat onto a table except this "book" pulverized itself. This is why the devastating "air blast" occurred killing one person and injuring others some distance away. The "air blast" was embedded with rock debris, wood fragments and dust traveling some 110 meters/second. This dirty air blast is what stripped trees bare and toppled about 1000.

Love your geology videos. Common wisdom states that to maintain brain health late in life it's important to learn new things. Now that I am 65 your videos should keep my brain going until I am 105 🙂

The fast direct approach up to the base of nw face of half dome is called the death slabs for good reason. A few year ago when we climbed the face we spent the night at the base on the far left side. Well, we awoke to a giant falling boulder that had peeled off the wall and tumbled all the way down to the valley floor. Which was our approach the morning before. Thankfully the climb went without issue but it’s shocking how often that area lets off rock!

Geeze Shawn-----you're like the geology whirling dervish-----Half Dome, Devils Tower, Iceland Volcano. You keep us on our toes---where next.

Great insight to Yosemite national park, didn't know the history dating back to the glaciers which occupied this are thousands of years ago, amazing its still so fragile . Wel done again Shawn, please keep this educational videos coming through! 👍👍👍😉

Thank you for featuring Yosemite in this video. We camp in the Yosemite Valley at least every other year and have done so in spring, summer and fall. We have been there when a crack on one side of the valley gave way and there was a rockfall. It was an eye-opener. Nature cares not if you are camping. Erosion does not wait for the folks on the trail to pass before letting go of a boulder. A number of deaths have happened when people stepped on a ledge that gave way (read the book "Off the Wall, Death in Yosemite). We have hiked to the top of Half Dome several times and to the top of the falls. Every time, it is a "crapshoot" people do not understand.

My husband and I have been to that Park. It was beautiful!

Thanks for the info about the granite in yosemite and it’s relation to ancient volcanic history. Just 45 miles southeast between yosemite and kings canyon on the south fork of the San Joaquin there are many hot springs, evidence of continuing activity on the west side of the sierras , would love to hear about what’s going on over there if you can make it out that way sometime.

from where you are right there, if you turned to the west, you can almost see hunters valley....the top of it at least. i went up there to the top of hunters valley and looked east. i was looking almost over el cap at half dome. the sheer face, i don't think i could see very far down though into the valley. good stuff there and b e a utifull place!

What looks like drill marks in that Granite Are from rock snakes

There's a really impressive area in remote northeastern Yosemite called simply "The Slide". It happened about 150 years ago, where a chunk of mountain about 1000 feet across and about 1000 feet above the canyon floor all came down at once. There are near house-size boulders along the creek at the bottom of the canyon and some boulders made it a ways up the other side. It's a mile or so from the nearest trail, just west of the Sierra crest. I was fortunate to see it on a free day during a trailwork trip in the area about 15 years ago.

Yeah I'm glad you added earthquakes as an event that can "get the ball rolling." One famous one was the 8.0 Owens Valley quake in 1872. The epicenter was in Lone Pine, a good 140 miles away; but it ruptured so abruptly that it cut a 50-mile-long scarp along Owens Valley -- and John Muir felt it strongly while he was living at Yosemite. He actually got to witness a MASSIVE rockfall in Yosemite Valley once the quake shook; I don't remember which part of the valley the rock fell but El Capitan keeps popping in my head for some reason. I'd have to review Muir's journal again to see exactly where that rock fell but it was massive. Perhaps the last earthquake of any size that precipitated rockfall in Yosemite; but they do happen and they don't have to be big ones.

Great lesson. Thank you! Have a wonderful Christmas!

How fascinating. Granitedoirite (sp) is my favorite rock. Especially that of the Mt Stewart batholith of Washington state. I have dreamed of seeing Yosemite, but life has not allowed it. It is interesting to learn of the forces at play within the granite itself from the formation underground but also pressure from glaciers. Yosemite Granite seems whiter than here in Washington. With the pressures and erosion from water and freezing, no wonder there are huge rock falls. Being a park geologist would be important and a dream job. Thank you for this lesson.

Greg Stock was an old caving buddy of mine in high school not too far from Yosemite. Very smart guy, knows that area better than almost anyone.

Yosemite always reminds me of Lauterbrunnen in Switzerland. They have a very similar look but I'm not sure if the geology and risks of rockfall are the same

Excellent as always.

I visited Yosemite Valley shortly after the large 1997 rock fall off Glacier Point. It was impressive to see how the hurricane force winds generated from the fall blew down a large swath of trees.

When I was an undergrad at Cal State, Stanislaus, I went up to Yosemite on weekends, hitch hiking up on Friday and back on Sunday. I did a lot of climbing, joining other climbers to do popular routes. During that time, all of us switched from using pitons to using chocks and cams for anchors because the older climbers had seen that cracks were being widened by driving the pitons into them and we all feared that some slabs might come off when we were using them for anchor points or standing on them. Some of the routes that I climbed have since been modified or eliminated due to rockfalls. Everything in Yosemite changes and the rocks always obey the law, of gravity.

Was hoping you would talk about the recent the crack on the western side of the Royal Arches just around the corner from where you made this video.

Yosemite is my beautiful backyard!

Yes,I remember in my climbing days there was a tremor that released boulders from the higher rims in the evening hours with sparking Bursts against the shear walls Quite a spectacle to behold!

These awesome videos are never a waste of time. This was fascinating - especially learning here why the granite rock walls tend to break away or “exfoliate” as you put it. I love this stuff because it offers new insight for us lay people.

Thank you

I wish you could stay on sabbatical forever! Love your videos!

Thanks again Shawn for making events understandable, your explanations are clear and concise. To your explanation you could also add "Gravity", the LAW that is always present 🙂

When I first saw Half Dome, my first thought was - where's the other half? :)

Very cool !!

Those saplings are incense-cedar or Calocedrus decurrens.

I remember reading about a rockfall fatality not far from Freerider, maybe a week after Alex Honnold's ascent.

I had not thought of glaciers there. Interesting. Thanks.

I lived in the valley for a number of years. I love that rock!

Or, those are 90 million year old drill marks that just happened to end up by the trail. Aliens!!! :)

A few days ago I coincidentally watched a documentary about Ansel Adams, the famous nature photographer of the 20th century. One of his best-known pictures was the Half Dome in dramatic light. And here we are with Shawn Willsey, showing us another aspect of exactly that landscape. Thanks so much.

Thx Prof ✌🏻 Excellent video

Hi! I knew you for your recent reports about Iceland and Grindevik crisis, very interesting stuff by the way, but this is a live-on-spot report type and it's also very interesting, possibly much more than webcam stuff. So thanx a lot for bringing an obscure italian guy in and around the majestic landscapes of your homeland and giving an inner view of it. Bye!

In 2015 there was a large rockfall off the NW face of Half Dome above and behind Ahwiya Point. Did any of that debris make it Tanaya Creek and the Mirror Lake area?

Thank you!

Thanks for your presentation! Though rockfalls are common, witnessing a sizeable one is a rare treat. Our small party had to take evasive measures when the weather during a late fall hike threatened to strand us on the wrong side of the Sierra crest. We used a cross-country route to arrive at a small timberline lake at the foot of a peak towering high above it on the opposite western side. After sunset but before darkness had descended on our camp, a sharp crack split the calm air, followed by a protracted din and dust cloud visible through the sparsely wooded view of the talus slope between the northeast face and the water. Nice to have that little bit of buffer between us and the very impressive demonstration!

I was there in 2002, some rockfall at night ( luckily) off Glacier point. In 2010 I went to The slabs below Glacier point and I think in 2009 there was a huge slide there that impacted the parking lots, we climbed anyway. We were right under the east end of El Cap and a few days later there was a big rock fall there. In 2015 when I was last there another big rock fall east end of El Cap.

Spectacular scenery and geology!

The term that park geologists use to describe rockfalls is “exfoliate” - the rock walls of the valley are constantly exlfoliating flakes of solid rock. There are piles of rocks like this all over Yosemite valley.

Another nice production by the wandering Willsey. Thanks bud. I’ve wondered where the other half of the dome is. Did it shear in half and get dragged away by the glaciers? Is it stuck below the current grade, waiting for the next ice intrusion to be exposed? I don’t ever recall hearing either the question or the answer. Might you shed some light on that, sir? Thanks again for the informative, well videoed and always pleasant production.

Very interesting and well presented. Definitely subscribed. Thank you!

Tenaya Canyon is so gorgeous. I made it to the waterslide once when I was young!

Search up the 1872 Owens Valley Earthquake when John Muir lived in Yosemite Valley.. I worked in Curry Village 1976 and hiked several of the trails to the rim.. Very special place in many ways..

Interesting information on a lurking dynamic among the stunning scenery. Thank you.

Very nice. Thank you! Well, it makes a nice home for rodents and rattlesnakes in all the openings.

We love our Granodiorite down in Idyllwild, Ca. I think of it as a miniature Yosemite.

Thanks

Stood atop half dome via the cable route and felt a strange, intense fear of the edge. Im seventy now and feel great to have been there and felt the fear so strongly. Intuition? Sure!

Wow I had no idea!

Now i know, which is a good thing!

Thanks!

So if you're walking in that area in march, some sort of sturdy hat might be in order. A tall stovepipe hat might offer some crumple zone.

Thank You again:-)

Yosemite is a beautiful wonder, no doubt about it. But it’s only 12 miles long. A beautiful canyon over 100 miles long can be found on Baffin Island, Nunavut, Canada in Auyuittuq National Park. If that’s too far, then Yosemite is a must see.

Your perspective below Ahwiyah Point makes it look much smaller than it really is.

Hi Shawn I’m still with you ,, I imagine that you might have some interesting segments about Yellowstone ,, 😊🙋🏻‍♀️😘

Ouch... Should always pack an Umbrella!

Once again, a great explanation of geologic processes, with all their complexities. I have been told that the Sierra that we see today is just the most recent of a series of mountain ranges that have risen and worn away -- is that true? --charles johnson, sacramento

Wow. So recent. Must have woken up a few campers.

9:30 squirrel

Sean if your in Reno anytime soon, i have a great hydrothermal altered Peg if you wanna check it out, very unique geology.

😳 I was unaware of the expansion concept, but it makes sense. How deep was the Half Dome granodiorite at crystalization?

Would pay for geology tours!!!

What is going on with all the mag 5 earthquakes along the Reykjanes ridge (24 in 48 hrs). I realize they're several hundred miles from Iceland, but along the same plate boundary.

Interesting video as usual. You are going to think I am a royal pain and hate rock climbers, but I really don’t! What I question is why are allowing rock climbing in these parks knowing the cracks in the rocks can cause the rock falls?

What do you make of the “hit and run” by Basil Tikoff? Wondering what your theory is on the formation on the Rocky Mountains. I’m seeing more and more that the farallon plate is definitely the cause of the Sierra Nevada, albeit there might be westward subduction into the terrains that accreted, and might explain a bit further how the Rocky Mountains came into being. I guess I’m not buying into the flat slab theory

What about freeze/thaw cycles?

Why is lava black in Iceland and Idaho, for example, but white ot nearly white here in Yosemite? Are there different / distinct pools of magma under the crust? Do they commonly and diffuse? Or do they remain distinct and unconnected?

When they call on the Emergency Geologist how many years do is take him to turn up?

❤❤❤❤❤

A 2.4 earthquake is miniscule IMHO ( former LA resident) Otherwise great video. Been to Yosemite a number of times

3:06 The scars on the rock face? There is something going on there that is not explained thus far. 3:20 It's the same on the other side. Those aint rock fall scars. I reckon you got it right with 'expansion'.

? Does (can) Aplite grade into Pegmatite?

Those are some attractive baby incense cedars among those boulders-

This rock is "Plutonic" in origin? Or Magmatic?

What you call a xenocryst I've heard called phenocrysts. What's the difference?

👍

Watch out for cryptids.

The greatest hazard in Yosemite is the 5million people who drive like maniacs (even though the speed limit is supposed to be no higher than 40 mph anywhere) as they race to the valley floor. Especially the L.A. residences who have NO time to enjoy the scenery ,people or animals on the way in or out.