El Capitan Rockfall: Alternate Views, and a Realization That This Wasn't the First TIme

El Capitan and the September rockfall from Taft Point on Oct. 29, 2017

Yosemite Valley changed geologically on September 27 and 28, and as I noted in my previous post, the valley will never look the same again. A series of rock falls resulted in a new scar on the east face of the east wall of the El Capitan cliff that can be seen from many points within the valley, including the iconic Tunnel View.

September rockfall from Taft Point on Oct. 29, 2017

I finally got to Yosemite Valley on Saturday, and got a few photos from the Tunnel View that I posted yesterday, but I was with students on a bus. Buses aren't allowed to stop just anywhere in the valley, so I was anxious to get back to the valley in my own car, and Mrs. Geotripper was all for visiting the valley, so we went back up there yesterday. The question, of course, was where to go for a good look? I definitely wanted an aerial view, so we headed up Glacier Point Road, the only route that allows for views from the rim of Yosemite Valley. Glacier Point offers views beyond belief, but only of the upper end of the valley. For a view of El Capitan, the "easy" choices are to hike to the top of Sentinel Dome, or to hike to Taft Point. Both hikes are about a mile and are not overly difficult. Sentinel is farther to the east and doesn't provide as good an angle on the cliff face that fell, so I headed out to Taft Point as the sun approached the western horizon.

The view is striking. The rocks let loose from well over a thousand feet over the valley floor. According to Greg Stock, geologist for Yosemite National Park, the biggest slab (out of seven total), was 394 feet long, 148 feet wide, and between 8 and 28 feet thick. That's bigger than a football field. It had a volume of 10,250 cubic meters, and weighed about 27,675 metric tons. If these numbers and dimensions seem incredibly exact, there's a reason. As Greg Stock explains, in an informative research paper, the walls have been mapped in three dimensions by a form of radar (lidar), and in the aftermath of the rockfall, the walls at the site of the fall were mapped again. The difference in volume could then be calculated.

El Capitan from Taft Point in 2005

I was at Taft Point in 2005, taking pictures of course, and one can compare the appearance of the cliff prior to the event in September.

Horsetail Falls area and future site of rockfall in 2005

The rockfall is also apparent from many spots on the valley floor. We headed to El Capitan Bridge, which offers an excellent straight-on view with the Merced River in the foreground. The white scar is unmistakable.

The Horsetail Falls cliff on Oct. 29, 2017

The difference between before and after couldn't be clearer. It's easy to miss the scale on cliffs this grand...remember, the missing slab of rock was bigger than a football field.

The cliff near Horsetail Falls in 2016

Another way to get a sense of scale is to add the 3,000 foot cliff of El Capitan to the scene...

El Capitan and the Horsetail Falls cliff on October 30, 2017

As I was going through my old pictures, I came to realize that slides have come off this particular cliff in the past. I actually witnessed one of them in 2010 when I was lounging on the granite near the top of Sentinel Dome across the valley. When I say "witnessed" I mean I heard the commotion first, took a moment to realize what I was hearing, jumped up, scanned up and down the valley, and finally thought to turn on the camera and take a few pictures of the rising dust plume.

Dust plume from the 2010 rockfall east of El Capitan

My account of that event can be found here: http://geotripper.blogspot.com/2010/10/rock-fall-near-el-capitan-in-yosemite.html. One can see in the picture below that the 2010 fall was just below the slab of rock that came down in 2017. One can imagine that the stresses on the cliff above were complicated by the event several years earlier.

National Park Service Rockfall Report for 2010

Dust rises from the El Capitan rock fall on October 11

Courtesy of Park Geologist Greg Stock, a review of mass wasting events in Yosemite National Park this year....

2010 Rock Fall Year in Review

Although not as newsworthy as those of recent years, many significant rock
falls occurred in Yosemite in 2010. The largest occurred on October 11
from the southeast face of El Capitan, midway up the cliff and along the
path of Horsetail Falls. This was actually the largest in a series of rock
falls from that area over several days. There were no associated injuries
despite the fact that these rock falls occurred during the peak of the fall
El Capitan climbing season. The cumulative volume of these failures was
approximately 1,700 cubic meters (5,000 tons).

Another area of notable rock fall in 2010 was the Rhombus Wall immediately
north of the Ahwahnee Hotel. This area was first active in August of 2009,
with subsequent failures in September 2009. Quiet for the early part of
2010, the cliff experienced renewed activity beginning in August, with at
least five rock falls radiating outward from the initial failure point
between August and November 2010. The cumulative rock fall volume over
this interval was 187 cubic meters (550 tons). This area of the Rhombus
Wall is an impressive example of a progressive failure due to stress
redistribution and crack propagation, and presents a unique opportunity to
learn more about this complex process.

Ironically, the most serious rock fall of 2010 was also one of the
smallest. On October 5, 2010, following several days of intense rain,
local children Serra Weber, Carmen Ortiz, and Angel Ortiz were playing on
the talus slope near the Church Bowl Picnic Area when a 1.7 cubic meter (5
ton) rock fell from low on the cliff. The rock fell directly onto Serra,
pinning her and causing life-threatening injuries. Carmen and Angel ran to
the nearby Yosemite Medical Clinic and notified the medical staff, who
responded immediately. Serra was flown to a local hospital where she
remained for several weeks. Serra recently returned to school in Yosemite
Valley, where she, Carmen, and Angel were honored for their bravery during
this event.

Other areas in Yosemite experiencing rock falls in 2010 include the
Porcelain Wall (on the western shoulder of Half Dome), Glacier Point,
Middle Brother, Middle Cathedral, Indian Canyon, and the Merced River
Gorge. In all, there were 59 documented rock falls in 2010, with an
approximate cumulative volume of 2,900 cubic meters (8,500 tons), more than
half of which derives from the El Capitan rock falls. For comparison, the
cumulative volume for 2009 was roughly 17 times greater, at about 48,120
cubic meters (142,000 tons); in that year the large volume was dominated by
the March 2009 Ahwiyah Point rock fall. Small rock falls are much more
likely to occur than large rock falls, but large rock falls represent a far
more important source of rock fall debris. The database of rock falls and
other geologic events in Yosemite, begun in 1857, now documents over 740
events, making it one of the longest and most detailed landslide databases
in the world.

It is very likely that there were additional rockfalls in 2010, but these
events either were not witnessed or went unreported. If you witness a
rockfall of any size, encounter fresh rock debris, or hear cracking or
popping sounds emanating from the cliffs, please contact park geologist
Greg Stock at (209) 379-1420, or at greg_stock@nps.gov, or contact Park
Dispatch. Predicting rock falls is not yet possible, but understanding the
events that do happen is an important step toward this goal. For more
information on rock falls and rock fall research in Yosemite, please see
the Park’s web page: http://www.nps.gov/yose/naturescience/rockfall.htm

Greg Stock, PhD, PG
Geologist
Resources Management and Science
Yosemite National Park

NPS Web Page Chronicles Yosemite Valley Rock Falls

Via Yosemite.blog.com, here is a link to a new web page on the rockfall history of Yosemite Valley. Besides a report on rockfalls in 2009 (there were 52), the page includes a wealth of links to other resources about mass wasting phenomena in the region. The map above chronicles the location of all the major rockfalls from 1857 to 2009.

It was a big year in the valley for this sort of thing. The Ahwiyah Rockfall actually changed the appearance of Yosemite as seen from the Wawona Tunnel and Glacier Point forever, and was the largest rockfall in 22 years. Luckily no one was hurt or injured.

Another Rock Fall in Yosemite

Photo from The Yosemiter

Ok, this really is a coincidence. I posted a couple of pictures recalling the Happy Isles rockfall of 1996, and this happens today in Yosemite Valley. A rock fall from the Royal Arches slightly damaged some parked cars, and forced the closure of the Ahwahnee Hotel until Friday so the chances of more activity can be evaluated. Boulders were the size of "microwave ovens".

Thanks to Loyd Schutte and the Yosemite Blog and the Yosemiter for up-to-date info. Thanks to Loyd for the morning photo link!
Update (8/27): links to pictures of the new rockslide on the Yosemite Blog here and here, and on Yosemite Trekker here (thanks, Loyd)

Rocks fall in Yosemite: Park Service closes 1/3 of Curry Village

Via the Yosemite Blog, the National Park Service has decided to permanently close down about a third of the tent cabins and other facilities in the Curry Village area of Yosemite Valley. The decision follows a series of rock falls over the last few years that have killed or injured several people. Investigations are seeking an explanation for an increase in incidents below the cliffs of the Glacier Point area.

The photo of the day shows some of the trees at Happy Isles that were snapped off by a huge rock fall in 1996 that killed one person and damaged the Nature Center.

Rocks fall in Yosemite? I had no idea that could happen!

I had one of those nice "convergence" moments today...I was discussing mass wasting in my physical geology classes today, and this story showed up on the front page of my local paper concerning the danger of rock falls in Yosemite Valley.

There was a rather nasty mass wasting event in the valley last month, and it has been noted that there have been four times as many rockfalls since 1996 than in the previous 139 (although I seriously wonder if this is because more attention is being paid to such events in recent years). If this is a true increase in the number of incidents, then the speculation that human interference is a causitive factor needs to be investigated. Most of the attention centers on water use at Glacier Point, the spectacular overlook on the rim of the valley. Some of the recent events have occurred in summer when visitation (and therefore water use) at the point is highest. Other researchers, including the park geologist, disagree with the contention that water plays a part in the recent events.

The other controversy concerns the placement of cabin units in Curry Village where many of the incidents have taken place. Curry Village took a hit when flooding in 1997 destroyed dozens of cabins, and proposals to remove more from the base area of the cliff would decrease housing units even more.

It was a great teaching moment...except that only four of my students had looked at a newspaper this morning.

Do Geologists Have a Death Wish?

Something about having a huge pile of laboratory notebooks to grade on a tight deadline brings out the sloth in me, and suddenly every little distraction takes on monumental proportions, and I just have to share. I just looked at, courtesy of Geology.com (http://geology.com/articles/yosemite-rockfall.shtml), a spectacular series of photos of a 2006 rockslide at Elephant Rock above the Merced River on Highway 140 just west of Yosemite, taken by Herb Dunn (http://herbdunn.com/). I am trying to imagine the excitement of witnessing significant geological events in action, and Herb had a seat right behind the plate so to speak. Check out the photos, they are spectacular.

The photo above, taken by yours truly, is decidedly not spectacular, but it represents the only time I have seen a rock fall in Yosemite, despite something like 50 or 60 visits over the last 20 years. It happened on April Fool's Day in 2000, and I only had a cheap film camera at the time (my digital age began in 2001). And what did I do? Immediately drove as close to the impact site as I could so I could check out any damage.

Seeing Herb's viewpoint (he actually didn't have much choice, with steep slopes and boulders all around), I considered what happens when events like this happen to geologists. We run for a better look! A landslide, a volcanic eruption, an earthquake, it seems like we can't resist; while others run away in a wild panic, I imagine many or most of us will be scrabbling for a camera and running towards whatever is going on.


It isn't a death wish, of course. Many times (but not all), geologists may have a different understanding of the risks involved (the story of Maurice and Katia Krafft and the events at Galeras volcano in Colombia do provide a cautionary tale). I, for one, find earth processes in all forms endlessly fascinating, and we geologists have a perspective that tells us that what we see may be a once-in-a-lifetime event. At the very least, we want to share our excitement with others. Then again, maybe we are crazy...

Geotripper, acting perfectly safe and sane....