Re: Half Dome Rockfall

Early morning Saturday, March 28, a large rockfall ocurred near Half Dome. (Ahwiyah Point?).
http://climbing.about.com/b/2009/03/30/yosemite-rockfall-near-half-dome.htm

So, do you really really really want to camp or hike in the valley?

FYI,
I was thinking that there were a lot of rockfalls this year. I guess not. About 500 since 1860's
Nothing special, just the record from the NPS website:



also look at http://pubs.usgs.gov/of/2003/of03-491/

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The cure for a fallacious argument is a better argument, not the suppression of ideas.
-- Carl Sagan

Vince: So, do you really really really want to camp or hike in the valley?

I think that I would be more aprehensive about driving the 140 (rockslide part) than I would be about being in the valley.

B

Poor, poor Mirror Lake. Filled in by erosion as we speak.

Vince wrote:

> Poor, poor Mirror Lake. Filled in by erosion as we speak.


One of the more remarkable aspects of Yosemite Valley for me is that the geologic forces (glaciers-->moraines-->lakes-->meadows-->forests) would seem to take thousands of years. I remember, however, when Mirror Lake was really reflective and deeper without the willow overgrowth and sedimentation (60's). I cannot think of any other feature of the valley that has changed so much, with so little human impact.

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The cure for a fallacious argument is a better argument, not the suppression of ideas.
-- Carl Sagan

Ahwiyah Point rock fall - A very large rock fall occurred from Ahwiyah Point near Half Dome at 5:26 am on the
morning of March 28. The rock fall originated near the summit of Ahwiyah Point and fell roughly 1800 feet to the floor of
Tenaya Canyon, striking ledges along the way. Debris extended well out into Tenaya Canyon, knocking down hundreds
of trees and burying the southern portion of the Mirror Lake loop trail. Reminiscent of the 1996 Happy Isles rock fall,
there appears to have been a small airblast associated with impact on the valley floor. Fortunately, due to the event
occurring in the early morning, there were no injuries. The impact generated ground shaking that was recorded by
numerous seismometers across California, registering as the equivalent of a local magnitude 2.5 earthquake. The volume
of the Ahwiyah Point rock fall is still being determined, but it was clearly one of the largest rock falls in the past decade;
for perspective this rock fall was many times the size of the recent October 2008 rock falls behind Curry Village.
Numerous smaller rock falls have occurred from Ahwiyah Point since the initial failure, and the southern portion of the
Mirror Lake loop trail remains closed until further notice.

Post Edited (04-01-09 22:06)
(Moved to another thread)



Post Edited (04-01-09 22:07)

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The cure for a fallacious argument is a better argument, not the suppression of ideas.
-- Carl Sagan

anyone have any pictures from mirror lake?

miguel wrote:
> anyone have any pictures from mirror lake?

My daughter was hiking in Tenaya Canyon on rockfall day and shot this photo of Mirror Lake at around 10:30 a.m.:



higher resolution:
http://rosano.com/yosemite/MirrorLake-28Mar09b.jpg

She was in a group of about 30 high school kids that had planned to hike the southern part of the loop first, but changed the plan and hiked only the northern part as far as the Snow Creek trailhead. They said there was a lot of dust in the air and it was hard to breathe.

I was in my tent cabin at Curry Village, awake and getting dressed at 5:30 a.m. when the rockfall occurred. I peeked my head out the door, and it sounded to me like it was happening in the West end of the Valley, towards El Cap (sound was echoing, I guess). I don't recall feeling the tent cabin shaking at all.

Here's a shot from the meadow adjacent to the Curry parking lot, taken at 6:00 a.m., about 20 minutes before sunrise and 30 minutes after the rockfall:



The dust in the air was noticeable, though at the time I didn't know it was dust from the rockfall.

higher resolution:
http://rosano.com/yosemite/2009-03-28at06_00b.jpg
(yes, the stars were out, and I did brighten the exposure a bit to better reveal the dust).

vdrummer wrote:

> She was in a group of about 30 high school kids that had
> planned to hike the southern part of the loop first, but
> changed the plan and hiked only the northern part as far as the
> Snow Creek trailhead. They said there was a lot of dust in the
> air and it was hard to breathe.

The water of Mirror Lake in that pic looks quite turbid, I assume that was from the rockfall??

Also, in the FYI category, granite produces silica dust and this can be injurious to the lung on a long term basis. In the perfect world, probably best not to intentionally breathe that stuff.

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The cure for a fallacious argument is a better argument, not the suppression of ideas.
-- Carl Sagan

Frank Furter wrote:

> vdrummer wrote:
>
> > She was in a group of about 30 high school kids that had
> > planned to hike the southern part of the loop first, but
> > changed the plan and hiked only the northern part as far as
> the
> > Snow Creek trailhead. They said there was a lot of dust in
> the
> > air and it was hard to breathe.
>
> The water of Mirror Lake in that pic looks quite turbid, I
> assume that was from the rockfall??

Yes, the folks on that hike said there was a layer of powdery stuff covering much of the northern part of the loop trail out there. They cut their hike short and played at Indian Caves instead, which were much cleaner. I led an alternate group of 23 kids up the Four Mile Trail; I didn't see any signs of the rockfall around Curry Village or anywhere else I went.

>
> Also, in the FYI category, granite produces silica dust and
> this can be injurious to the lung on a long term basis. In the
> perfect world, probably best not to intentionally breathe that
> stuff.
>

vdrummer wrote:
. They cut their hike short and played at Indian Caves
> instead, which were much cleaner.

Can you clarify exactly how to get to the Indian Caves? There seems to be vague and conflicting information on the Internet about them.

---

The cure for a fallacious argument is a better argument, not the suppression of ideas.
-- Carl Sagan

Frank Furter wrote:

> vdrummer wrote:
> . They cut their hike short and played at Indian Caves
> > instead, which were much cleaner.
>
> Can you clarify exactly how to get to the Indian Caves? There
> seems to be vague and conflicting information on the Internet
> about them.
>

Indian Caves are right around N 37° 44.68' W 119° 33.3' (aka 37 deg 44 mins 38 secs N, 199 deg 33 mins 20 secs W), about a half mile west of Mirror Lake along the trail that runs along the North side of the Valley, below Washington Column and East of Royal Arches. You can also get there by going just about directly North from Tenaya Bridge, which may be indicated on your favorite topo map.

I wouldn't call it an exact, specific spot on the ground, but rather a broad pile of large scree and rockfall that is great for rock scrambling and such. From the Awahanee Hotel, it's about 2/3 of the way to Mirror Lake along the trail that runs along the North edge of the Valley.

I was planning on hiking to half dome in early May for the first time. Is this not possible anymore?

bman0621 wrote:

> I was planning on hiking to half dome in early May for the
> first time. Is this not possible anymore?

The rockfall would have zero effect on the route going to Half Dome. The rockfall occurred on the face of Half Dome and not any trail leading to the cables. The trail now covered by rocks is the Mirror Lake Trail.

The cables are still down for the season (NPS says they're typically up the 3rd week of May), but I suppose anything is possible. I have heard of people going up the cables even when they're down. It's not illegal although the NPS probably discourages people from doing it because of the risk. I'm not sure how much snow there might be this time of year. Avalanches possibly damaging the cable supports is the usual reason given for taking them down before the snow hits.

Two of the three fatalities between Nov 2006 and June 2007 on the HD cables were from people who attempted to climb up HD when the cables were down. One of them was someone who was a marathon runner and might have gotten a little too carried away with what she thought she was capable of. Apparently she tried this with clouds overhead, which isn't even recommended when the cables are up because of the risk of lightning strikes and the granite getting slippery. Her name was Jennie Bettles and apparently she had started doing stuff like 50k trail runs and other endurance activities. She may have been fit, but there's no sane reason why anyone should attempt to go up the cables in those conditions. The risk of lightning at the top is enough reason to skip it. The woman who fell off in Nov 2006 apparently slipped going down because it was wet. I wouldn't go up Half Dome when the cables are down, but doing so when it's wet is a monumentally bad decision.

y_p_w wrote:


> The rockfall would have zero effect on the route going to Half
> Dome. The rockfall occurred on the face of Half Dome and not
> any trail leading to the cables. The trail now covered by
> rocks is the Mirror Lake Trail.
>

Now if a person decided to take a really long way to Half Dome via the south loop of the Mirror Lake trail and up Tenaya Canyon to Omstead Point then to Clouds Rest and down to Half Dome , then the rockfall would limit that route.

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The cure for a fallacious argument is a better argument, not the suppression of ideas.
-- Carl Sagan

Please look here:

http://www.nps.gov/yose/planyourvisit/conditions.htm

If direct response to your question...
The cables may not be up yet.

Check that link above before you go to see if they are.

http://www.supertopo.com/

Has a great picture of the rockfall.
I'm looking forward to getting a good one this weekend too...

bill-e-g: Has a great picture of the rockfall. I'm looking forward to getting a good one this weekend too...

I wonder if rockfalls are like earthquakes: Aftershocks! (don't get too close)

B