Importance of Natural Resources

Yosemite Nature Notes – 12 – Glaciers


[Music] [Music] While many people think
of Yosemite Valley as a great place to look
at evidence of glaciers, as you come up into the
High Country of Yosemite, Olmstead Point,
Tuolumne Meadows, you find even better evidence
for the recent passage of ice. But to see the living
glaciers still at work at the crest
of the Sierra, there is nothing that compares
to seeing this in action. Here is a
field of ice formed from millions and
millions of snowflakes slowly working on the
mountainside, sliding downhill, just like they have off and on for tens and
hundreds of thousands of years. Well, in the Sierra Nevada, you really only get glaciers
at the very highest elevations, near the highest
peaks and the range, they are usually tucked
up into seracs that mostly face
North or Northeast. So they’re generally pretty
remote places, hard to get to. So I’m standing here on the
summit of Mount Maclure and looking out over
the Lyell Glacier. That’s Mount Lyell
right there; the highest point of
Yosemite National Park, just over 13,100 feet, and beneath it is
the Lyell Glacier, which is the largest
glacier in the Park. It’s the second largest glacier
in all the Sierra Nevada and the largest glacier
on the Western slope of the mountain range. And there are no trees
at this elevation. There is not much soil. There aren’t many plants. It’s a fairly
barren landscape, often windy, intense solar energy,
intense ultraviolet. So not a friendly place, unless you really
like this alpine zone and you want to
see a glacier. There are some elements
of danger here. This is a really
dynamic place. The ice is moving, the rocks are moving, and to explore it,
you have to be careful. The moraines are
fairly unstable, so there are a lot
of loose rocks there. You can tip a rock over onto
yourself if you are not careful. For the most part, the Lyell
Glacier is sort of big and open and easy to get around on, but
it’s still steep and slippery. It’s late summer,
early autumn and this is kind of a typical
scene up on the Sierra glaciers, what we call sun cups,
these fence, steep fence of
snow and ice, and they make it
really challenging for travel. The Maclure Glacier has some big
crevasses and big holes in it, and so you actually need
to be really careful moving around
on that ice. Alright! Now
we’re about two-thirds of the way
up the Maclure Glacier. It’s pretty gentle
slope, lots of sun cups. It steepens up above us. There’s signs of crevasses
starting to show some open gaps. This is a crevasse here
on the Maclure Glacier and a crevasse is basically
a big fissure or a chasm in a glacier that forms as the
glacier is moving down slope. The down slope side will
move a little bit faster than the upslope
side and create essentially a
tear in the glacier, and these crevasses can be hundred or many hundreds of
feet deep in some cases. One of the really interesting
things about the Maclure Glacier is that at the toe of the
glacier is an ice cave, and you can get
into that cave and see the bottom
of the glacier, see where the glacier is
sitting on the bedrock. And so a lot of these features
that we see in Yosemite that are 15,000 or
20,000 years old, we can see forming today
underneath the Maclure Glacier. So by definition, a glacier is
a mass of ice that’s moving, flowing and sliding down slope. In the case of the
Maclure Glacier here, we have measured that
movement by tracking the stakes that we
put in through time, and we know that it moves
about 20 feet a year. But there is
another way to get a sense of the
movement of the glacier and that’s to actually
come down inside of it, in a place called
the Bergschrund, which is a big crevasse that
forms between the cliff and the glacier itself. That’s pretty cool. Alright, now we are
in the Bergschrund of the Maclure
Glacier, which is propelled
probably 25 feet, and we’re really kind of
inside the glacier now. This right here
is bedrock. This is the headwall
of the serac that the glacier
is formed in, and this side
here is the ice. And so this right here is a
really good demonstration and visualization
of glaciers sliding. This wall behind me here used
to be flushed with the bedrock and it’s pulled away,
leaving a space, and giving us a very
visual demonstration of how glaciers move. So I’ve been
coming onto the Mount Lyell Glacier
for 20 years. I’ve seen it change from the
first time I came up here, till now, and gradually I’ve watched it
get smaller, more rock show, the classic features of glacier
kind of slipping away, and it’s almost like watching
Half Dome melt away or dissolve. Well, these glaciers pose
an interesting challenge for resource managers in the
National Park Service. They are actively
retreating. They are changing
very quickly, but there is not a lot that we
here in Yosemite National Park can do about that, because every
indication is that these glaciers are
retreating in response to a globally changing climate, and so everybody is
kind of responsible for trying to manage
these glaciers in that sense. So things have changed, not
just in the Park’s environment, but outside the Park’s
environment that effect what we consider a
very protected land, our Yosemite is protected,
it’s designated wilderness, it’s a world
heritage site, but it’s not disconnected
from the rest of the world. And the sense is
that this glacier will disappear within
a few decades, and that will
be a loss to the wholeness of our
environment of Yosemite. The Lyell Glacier here,
as it retreats, will just keep
moving up the slope until it finally gets right
underneath the summit there and it will disappear. And there are a number of
other plants and animals that are doing effectively
the same thing, and the ones that
are living at the very highest peaks
in the Park, eventually they’ve
got nowhere to go. I mean, that’s the top of the
Park right there, Mount Lyell. For the things that are
up there right now, when the temperatures
get a lot warmer, they’re not going to be
able to go anywhere, and like the Lyell Glacier
here, they too may disappear. In the bigger sense, it is just
cool that Yosemite has glaciers. To me, it’s an attractant. It’s an element of Yosemite
that adds to its wildness, its mystery, its antiquity,
and ancientness. You don’t have to go to
Alaska or Greenland or Antarctica to see ice, you can go to Yosemite National
Park and hike for a day, up to the highest peaks
and see these glaciers.


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