00:00:25
This is actually a really
interesting viewpoint
00:00:27
to view the runout zones for
rockfalls from Glacier Point.
00:00:34
Usually we're looking
either across the Valley
00:00:36
over at Glacier Point,
00:00:38
or we're down at
the bottom looking up,
00:00:40
and those are valuable
views as well,
00:00:42
but this is really useful
to be able to be up here
00:00:46
And from right here I
can see runout zones
00:00:48
for about five different
rockfall events
00:00:50
that have occurred in
the past decade or so.
00:00:55
The cliffs are eroding very
slowly, grain by grain,
00:00:58
all the time, but when suddenly
a piece of the cliff
00:01:03
that's 200 feet wide
and 100 feet tall
00:01:05
and 20 feet thick just
falls off the cliff
00:01:09
and falls 1,000 feet
to the Valley floor
00:01:11
and breaks up in
all these pieces,
00:01:13
you know, that's a really
different style of erosion.
00:01:18
When we look around
Yosemite Valley,
00:01:20
we see abundant evidence that
rockfalls have been occurring
00:01:22
here for thousands of years.
00:01:39
Yosemite Valley is a
glacially carved canyon,
00:01:42
and since glaciers retreated
about 15,000 years ago,
00:01:45
rockfall has been
the major force
00:01:48
shaping this landscape.
00:01:50
We don't always know
what causes a rockfall
00:01:52
in a particular event.
00:01:54
Sometimes it's
obvious in that
00:01:55
there might have been a
large rainstorm or snowstorm
00:01:58
that then caused a lot of
seepage and so we surmised that,
00:02:02
that seepage must have
caused the rockfall.
00:02:04
It's not always the
case, sometimes
00:02:07
rockfalls happen without
any known trigger,
00:02:09
so it could just happen on a
nice bright summer, sunny day.
00:02:13
We had decided to rent bikes
to ride around the Valley,
00:02:16
we were only here
about an hour and
00:02:19
heard this loud
thunderous roar and
00:02:24
couldn't tell where the
sound was coming from.
00:02:26
And looked around and I saw a
rock falling off the wall
00:02:30
over to my right.
00:02:34
Whoa, a rockfall, look!
00:02:42
I had to get my camera off the
bike as quickly as I could,
00:02:44
that's why the
footage is a little shaky.
00:02:47
I had to take the wide
angle lens off of it
00:02:50
and was lucky enough to
catch the third rockfall.
00:02:59
Look at that piece!
00:03:17
In the particular rockfall
that was captured on video,
00:03:20
you can see a rock slab
detaching from the cliff face,
00:03:26
sort of skipping down
the cliff face,
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