Re: Ahwiyah Point Rockfall Size Estimated

On March 28, 2009, a large rockfall occurred from Ahwiyah Point near Half Dome. Rocks fell roughly 1,800 feet, knocking down hundreds of trees and burying hundreds of feet of trail on the southern portion of the Mirror Lake Loop Trail. The impact generated ground shaking equivalent to a magnitude 2.4 earthquake. Numerous smaller rockfalls have occurred from Ahwiyah Point since the initial rockfall on March 28. There were no injuries or structures affected.

The approximate volume of the initial rockfall is 43,000 cubic meters, or 115,000 tons. This is considerably larger than the 1996 Happy Isles rockfall, which was estimated at 30,000 cubic meters in volume. Therefore, this rockfall is the largest one in Yosemite National Park since the 1987 Middle Brother event.

Due to the debris and trail coverage, the southern portion of the Mirror Lake Loop Trail is closed to hikers indefinitely.

Because of the most recent rockfall activity around Yosemite Valley, there has been speculation that rockfall has become more frequent. Based on historical databases and recent events, park geologists are unable to discern a geologically significant increase in rockfall activity in Yosemite Valley.

Rockfalls are a natural and dynamic geologic process. Due to its steep, glacier-carved cliffs, Yosemite Valley experiences many rockfalls each year. Natural processes like rockfall help to create the beautiful and changing scenery in Yosemite National Park.

eeek wrote:

>
>
> The approximate volume of the initial rockfall is 43,000 cubic
> meters, or 115,000 tons. >
>

I wonder how they measure that sort of thing. Do they actually map the lost area length, width, depth?

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

Frank Furter wrote:

> I wonder how they measure that sort of thing. Do they actually
> map the lost area length, width, depth?

Maybe this will help:

http://blog.wired.com/wiredscience/2008/10/geology-20-20-g.html

eeek wrote:
> Rockfalls are a natural and dynamic geologic process. Due to
> its steep, glacier-carved cliffs, Yosemite Valley experiences
> many rockfalls each year. Natural processes like rockfall help
> to create the beautiful and changing scenery in Yosemite
> National Park.
>
Still, we all hope the scenery doesn't "change" while we're looking up at it...8^)

I'm surprised it's so much larger than the '96 one at Happy Isles. I remember hearing about visibility being low, breathing the air being dangerous, and the huge wind blast that leveled so many trees. Seems this one just happened, and aside from here, there's not been a lot said.

Too bad about the south loop though; that was one of my favorite winter-season easy but scenic hikes. I remember running into a somewhat intimidating herd of these guys
http://www.pbase.com/roberthouse/image/65127876
right about where the rockfall should be.

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Gary
Yosemite Photo Galleries: http://www.pbase.com/roberthouse/yo

Sierrafan wrote:

> Still, we all hope the scenery doesn't "change" while we're
> looking up at it...8^)

Or standing on it!

Does this mean no more Mirror Lake loop?

Vince wrote:

> Does this mean no more Mirror Lake loop?

It's a bit bumpy right now.

eeek wrote:
> > Still, we all hope the scenery doesn't "change" while we're
> > looking up at it...8^)
>
> Or standing on it!
>

Good point (Ahwiyah, that is).

From the Half Dome trail we always go out there to the edge just before the granite starts to enjoy the view. Seems like that must be at or near Ahwiyah Point (?). It's easy to spot from below, from above it's not as obvious I guess.
Below:
http://www.pbase.com/roberthouse/image/61720905
On top
http://www.pbase.com/roberthouse/image/111117160
http://www.pbase.com/roberthouse/image/97693609
Or I guess that's about where it is.

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Gary
Yosemite Photo Galleries: http://www.pbase.com/roberthouse/yo

Sierrafan wrote:


> From the Half Dome trail we always go out there to the edge
> just before the granite starts to enjoy the view. Seems like
> that must be at or near Ahwiyah Point (?).

Is it in this photo?

http://www.spinics.net/f/yosemite7-125JPG.html

These are two pics Dale took at the Slide Mountain rock fall:

<http://picasaweb.google.com/dale.dekeyser/Yose#5244132766047892482>;

<http://picasaweb.google.com/dale.dekeyser/Yose#5244132776542158642>;

Posted with his permission I hope.

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Old Dude

Here's the GP fall from Sierra Point.

<http://picasaweb.google.com/dale.dekeyser/SierraPoint#5321420696812305778>;
<http://picasaweb.google.com/dale.dekeyser/SierraPoint#5321420767979824530>;

As long as I get some cooperation I'll get some sweet shots of the
Ahwiyah Pt. rockfall this weekend...

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Everything I know I learned from

bill-e-g wrote:

> Here's the GP fall from Sierra Point.
>
> <http://picasaweb.google.com/dale.dekeyser/SierraPoint#5321420696812305778>;
> <http://picasaweb.google.com/dale.dekeyser/SierraPoint#5321420767979824530>;
>
> As long as I get some cooperation I'll get some sweet shots of
> the
> Ahwiyah Pt. rockfall this weekend...
>

In photo 15 you are above Sierra Point. Was that intentional or did you get off track?


Very nice pic's, Sierra and Slide Mt. bytheway!



Post Edited (04-09-09 11:56)

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

http://www.nps.gov/yose/parknews/ahwiyahrockfall.htm

They have a few nice pictures of it. It be big...

All of these are from Sierra Pt. / to and from Sierra Point.
Intentional. Sweet Trail...
I posted this same stuff in eeeeek's "Sierra Point" post:

This was last Sunday. April 5

<http://picasaweb.google.com/dale.dekeyser/SierraPoint#>;

joe_schmo wrote:

> Sweet Trail...

Trail? You call that a trail?

>In photo 15 you are above Sierra Point. Was that intentional or did you get off track?

Ok, I get it now...

Yeah, that was intentional. The very last little section skirts around the
rock I was on taking picture 15.
The trail is very obvious. Very easy to follow...

But... not my fault if u take it... don't recommend you take small children
and recommend you bring hiking sticks to help you on the way down.
(we all know it is easier to climb up than climb down...)

eeek,

After taking the "old" trail up Northwest from Poopenaut Valley a
couple weekends ago. YES... that is a sweet trail..

joe_schmo wrote:

> eeek,
>
> After taking the "old" trail up Northwest from Poopenaut Valley
> a
> couple weekends ago. YES... that is a sweet trail..
>
>


The first part of "it" that I did wasn't even close. But I was way off track at that point due to wetwear memory fault.

pict #1 is in the middle of the rockfall. You can still see the trail and people on the trail to Vernal from there..
pict #2 is taken in same spot. If you look close on the tree there is an arrow... which is in pict #3.
From there... trail is obvious IMO... there are even ducks/cairns in places
#7 might give people some pause. where'd it go???
Up and to the left...



Love the "trail". Jump into the woods away from the masses and
didn't see anyone until got back on the asphalt...

joe_schmo wrote:

> Love the "trail". Jump into the woods away from the masses and
> didn't see anyone until got back on the asphalt...
>

I got a big shock when two guys came around the corner just before I got to the end. And then there were two people at Sierra Point itself.

>Is it in this photo?

No, you cannot see Ahwiyah Pt. in that photo.

Gary's first photo is a nice shot of the point. His other 2 are cool...
but you cannot see the point in either of those.

If you want some other view you can look here:
#2 and #8 have the point in them
<http://picasaweb.google.com/dale.dekeyser/Tenaya08#>;

#58 is pothole dome Queenie Bee.



Post Edited (04-09-09 17:28)

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Everything I know I learned from

Bill-e-g: #58 is pothole dome Queenie Bee.

I will buzz right over there and take a peekie (you know, so I am sure that I am at the correct dome!)

B

Yes, I just wondered how it (Ahwiyah) looks from the top. Usually when we get to that area it's on a dayhike to Half Dome, with the worst part (granite steps) ahead, so I'm not prone to do a lot of exploring in that area except to enjoy the view for a few minutes. I assume you could cut off the Half Dome trail somewhere in there and get to Ahwiyah point, but don't know that for sure...there are a lot of steep dropoffs along the canyon there. Looks like you'd have to cut over toward Half dome but in front of where the rocky sub-dome climb begins. If that's possible. Or wise 8^).

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Gary
Yosemite Photo Galleries: http://www.pbase.com/roberthouse/yo

I doubt you can see anything from the south side.

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Old Dude

Ok. You do realize that the Pt. is 1000 ft. below the first dome?
1900 ft. below the top of Half Dome?

You'll be needing ropes.

From the top of Half Dome:
<http://picasaweb.google.com/dale.dekeyser/Yose#5322921050887408770>;
<http://picasaweb.google.com/dale.dekeyser/Yose#5322921095592916018>;

From Watkins:

or
<http://picasaweb.google.com/dale.dekeyser/Yose#5322921004731643794>;

Piece of cake. I'll stop by there next month on the way up Half Dome. 8^)

Looks like if you fall off the cables, you'd be able to see it on the way down; I've seen many water bottles go by that probably got a great view of Ahwiyah point for a short time...

Actually, it did answer what I wondered; it's hard to tell from below just how far below HD it is, and whether it's accessible. Looks like pretty far and not really.



Post Edited (04-10-09 09:30)

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Gary
Yosemite Photo Galleries: http://www.pbase.com/roberthouse/yo

Gigapan image of the rockfall:

http://share.gigapan.org/viewGigapan.php?id=20475&window_height=990&window_width=1577

Let me know if this doesn't show up.
The rock fall is HUGE.