this is actually a really interesting
viewpoint to view the run-out zones for
rock falls from glacier point usually
we're looking either across the valley
over at Glacier Point or down at the
bottom looking up and those are valuable
views as well but this is really useful
to be able to be up here and look down
and from right here i can see run out
zones for about five different rockfall
events that have occurred you know in
the past decade or so the cliffs are
eroding very slowly grain by grain all
the time but when suddenly you know a
piece of the cliff that's 200 feet wide
and a hundred feet tall and 20 feet
thick just falls off the cliff and falls
thousand feet to the valley floor and
breaks up in all these pieces you know
that's a really different style of
erosion
we look around you somebody Valley bc
abundant evidence that rock falls have
been occurring for thousands of years
yosemite valley is a glacially car
canyon and since glaciers retreated
about 15,000 years ago rockfall has been
the major force shaping this landscape
we don't always know what causes a
rockfall in particular event
sometimes it's obvious and that there
might have been a large rainstorm or
snowstorm and then caused a lot of
seepage and so we surmise that that
seepage must have caused the rockfall
it's not always the case sometimes
rockfalls happened without any node
trigger so it could just happen on a
nice bright summer sunny day we had
decided to rent bikes to ride around the
valley we only hear about an hour and
heard this loud thunderous roar and
couldn't tell where the sound was coming
from and looked around and I thought
rocks falling off the wall over to my
right
black koala
how to get my camera off the bike as
quickly as I could
that's why the footage is a little shaky
how to take the wide-angle lens off of
it and was lucky enough to catch the
third rockfall
play that piece
in the particular rockfall that was
captured on video you can see a rock
slab detaching from the cliff face sort
of skipping down the cliff face hitting
a prominent ledge breaking up into a
bunch of pieces and some of those
individual pieces are 40 50 feet on the
side and those pieces that are free
falling through the air spinning on
their way down they fall several hundred
feet and then they impact the talus
slope at the bottom
and some of those huge boulders will be
moving down the talus slope at 40 50
miles an hour
snapping large trees like matchsticks
and going all the way down to the base
of the talus slope in the valley floor
was standing at the base of the rockfall
that happened on august 26 of last year
2009 and this is one of the rocks that
fell from it
I thought they were about that big you
know because we're about a half mile
away so they didn't seem that big but
now looking at it there it's there yuge
it's amazing to think that came down
from up there and then bounce i guess it
must have bounced right and prior to
august of 2009 this slope at large oak
trees on it but when several thousand
tons of rock came down off the cliff and
landed in this area and then move down
the talus slope those boulders basically
wiped out all the trees that were on
this slope and this talus slope leads
right down to the floor of Yosemite
Valley and just beyond the edge of the
talus slope is the want a hotel if these
Rock Falls were occurring in a remote
valley they would be of scientific
interest only but because these Rock
Falls are occurring in Yosemite Valley
narrow Valley with nearly four million
visitors a year they are more than a
spectacular natural process depending on
where and when a rockfall occurs it can
have potentially serious consequences in
1971 in 1972 there were two large rock
falls they came off the face of elephant
rock this was the impact area for the
March 1987 middle brother rockfall this
is the impact area for the July tenth
1996 happy isles rockfall this Boulder
hear that i'm standing on roughly 400
ton Boulder that came down in October of
2008 so this Boulder here is an old
rockfall boulder and you can tell that
this is an old rockfall boulder because
it's covered in lichen and moss it's not
a fresh boulder now in contrast this
Boulder here is fresh it has no moss or
lichen growing on it and this Boulder is
just like those other boulders that came
down from early
Rock Falls the differences when this
Boulder came down in October of 2008
these structures were here in Korea
village and the consequences of that are
obvious a scary situation hitting
visitors at Yosemite today for the
second time in as many days a rockslide
is it the parks Curry Village area we're
getting some eyewitness accounts of that
rock slide that hit this morning sending
people running and crying in fear and
there are some unconfirmed reports of
injuries in that area and we've got some
pictures from kcra3 livecopter3 HD was
over the scene of that walk slide this
morning that took place at about seven
o'clock our primary concern is saving
people's lives 15 people have died from
rock falls in yosemite national park in
the last 150 years and that's not an
insignificant number it is much smaller
than the number of people that have died
in Yosemite streams and rivers and it's
certainly much smaller than the number
of people that have died in traffic
accidents but one big rock fall at the
wrong place at the wrong time could
dramatically increase that number and
that's why we are focusing on learning
everything we can about rockfalls using
laser scanning computer modeling
monitoring of the cliffs but the scope
of trying to understand all these
complexities and all of these different
rock faces to a point where we can start
to predict rockfalls is going to be
really challenging predicting Rock Falls
is a very difficult scientific question
to go after it similar to predicting
earthquakes you know rockfalls can
happen anytime and so we're interested
in determining how often and when
essentially where
so much of what we know of the assembly
landscape the iconic clips of El Capitan
and Half Dome the forest to talus slopes
the big boulders out the floor of the
valley all these features
oh they're existence to rock falls and
Rock Falls have been occurring in
Yosemite for thousands of years and they
will continue for thousands morale
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