Maclure Glacier

Transcription

[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.