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gstock
climber
Yosemite Valley
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Topic Author's Original Post - Feb 5, 2013 - 01:03pm PT
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This may be of interest to those of you who frequent the High Sierra. I suspect that this story is playing out on glaciers across the range.
Yosemite National Park's Largest Glacier Stagnant
Lyell Glacier Ceases Movement, Adjacent Maclure Glacier Moving at Historical Rate
The Lyell Glacier, the largest glacier in Yosemite National Park, has stagnated, or ceased its downhill movement, according to a recent study conducted by scientists from the National Park Service and the University of Colorado. The adjacent Maclure Glacier is still moving at its historical rate, about one inch per day.
Glaciers created much of the scenery of Yosemite, including iconic features such as Half Dome. Glaciers are defined as long-lasting ice masses that arise from the accumulation of snow, and move downhill by flowing and sliding. A glacier's health is determined by the amount of winter snowfall compared to summertime melting of snow and ice. The movement of a glacier is primarily determined by the glacier's thickness and steepness. Because they are sensitive to environmental conditions, glaciers are important indicators of climate change.
Building on historical research conducted by John Muir and other notable individuals in Yosemite's history, the research team monitored the Lyell Glacier and the Maclure Glacier, deep in Yosemite's high-country. Movement of the glaciers was monitored by placing stakes in the ice and tracking their positions over a four year period.
Data collected from the stakes placed on the Lyell Glacier showed that no movement has occurred within the last several years. Earlier research on the glacier showed that it was moving in the 1930's. Stagnation has therefore occurred since that time, perhaps within the past decade. In addition, the Lyell Glacier has decreased in size by about 60% since 1900, and has thinned by approximately 120 vertical feet. This thinning of the glacier is most likely why the glacier has stopped moving.
"The Lyell Glacier has historically been recognized as the largest glacier in Yosemite National Park and the second largest in the Sierra Nevada," said Yosemite National Park Geologist Greg Stock, who co-led the investigation with Robert Anderson of the University of Colorado. "However, the lack of movement suggests that the term 'glacier' no longer accurately describes this feature."
The team also measured the Maclure Glacier, which is adjacent to the Lyell Glacier. John Muir first documented movement of this glacier in 1872. The research team mimicked Muir's measurements in 2012 by measuring stakes over the same period of the melt season. Despite a similar amount of ice loss as the Lyell Glacier, the team found that the Maclure Glacier continues to move at the same rate as that measured by Muir, about one inch per day. Although the Maclure Glacier has also thinned substantially, it is still thick enough to move and flow. Much of the downhill movement occurs by slow sliding at the glacier bed due to increased amounts of meltwater.
Research on the glaciers will continue to be conducted through collection of data on snowpack, temperature, and ice melting rates. Guided by records of the local climate archived in the widths of tree rings in nearby forests, the research team will also create a model to show the change in size of the glaciers over the past 300 years. This model will provide insight into the future health of these ice masses.
This work contributes to the growing evidence of ice loss worldwide. The differing behavior of the adjacent Lyell Glacier and Maclure Glacier illustrates the complexity of the landscape's response to climate change. However, the fact that both glaciers are shrinking - causing the Lyell Glacier to cease movement -highlights the impact that a changing climate is having in Yosemite National Park.
Funding for this research project was provided by the Yosemite Conservancy.
Yosemite National Park has a robust research program. The park issues approximately 120 research permits per year, covering a wide array of natural, cultural, and social science subjects. Park scientists collaborate with researchers, mostly from universities and the US Geologic Survey, on the scientific research conducted in the park. Current research topics include studying a tract of old growth forest in the park, the decline of amphibian species in the high-country, and using remote sensing to measure the snowpack.
http://www.nps.gov/yose/parknews/lyellglacier.htm
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klk
Trad climber
cali
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thanks greg
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Reilly
Mountain climber
The Other Monrovia- CA
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Now it is on par with most SuperTopo participants.
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BooDawg
Social climber
Butterfly Town
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XLNT Greg! Sounds like fun and interesting "work." But someone's gotta do it!
LOL!
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scooter
climber
fist clamp
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As Yosemite Valley was once filled with ice in the ,geologically recent past, what is the point of stasis that the measurement of how much ice should be on Earth vs. should not? Is there a year or epoch that scientist concur on as to when we had the perfect amount of ice?
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JEleazarian
Trad climber
Fresno CA
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Now it is on par with most SuperTopo participants.
LOL!
Interesting stuff, as your posts always are, Greg. Thanks.
John
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rottingjohnny
Sport climber
mammoth lakes ca
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Reilly...We started stagnating once the boob thread was deleted...What else is there to look forward to other than watching paint dry...? RJ
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splitclimber
climber
Sonoma County
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aren't they tracking the conness glacier as well? or is it a different research group than the Yosemite group?
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10b4me
Boulder climber
Somewhere on 395
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thanks for the info.
just curious, if there is the same out of loss on both the Lyell, and Maclure glaciers, why is the Maclure still moving? is it because of the melt water? wouldn't melt water allow the Lyell to move also? very interesting.
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gstock
climber
Yosemite Valley
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Topic Author's Reply - Feb 5, 2013 - 03:18pm PT
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That's a good question, and one we don't have a simple answer for. I strongly suspect it comes down to thickness; a glacier will flow once it has sufficient thickness (and slope, which isn't changing here), and conversely will stop flowing when it thins below that threshold - perhaps 150 feet thick or so. Lyell appears to be thinner than that, while the Maclure is probably thicker. Because it is still moving, the Maclure Glacier has many crevasses which allow meltwater to get to the bed and enhance sliding, so there is a positive feedback there, at least for now. The Lyell Glacier no longer has crevasses.
A group from UC Berkeley was monitoring stakes on the Conness Glacier, but I believe they had problems with the stakes melting out during the summer. We hauled in a steam drill to sink our stakes about 15 feet into the ice but still they nearly melted out after a few years.
QITNL, I was up there at that time so we probably did meet. With ice augers, PVC poles, and GPS antennae sticking out of our packs, we tend to attract a lot of attention on the trail.
Greg
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RP3
Big Wall climber
El Portal/Chapel Hill
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Poor Lyell...
Great work, Greg et al.!
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10b4me
Boulder climber
Somewhere on 395
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Greg, thanks for your answer.
I climbed Lyell in 1980. seems like we stepped off the glacier onto the summit.
How thick is the Conness glacier?
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RP3
Big Wall climber
El Portal/Chapel Hill
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From a distance, it looks the granodiorite of the Kuna Crest (makes sense given where you found it.
The "tortoise-shell" surfaces are a bit confusing to me. My hunch is joint surfaces. I find it hard to believe that they are glacial polish given that it is present on both sides.
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gstock
climber
Yosemite Valley
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Topic Author's Reply - Feb 5, 2013 - 05:25pm PT
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QITNL, great photos, thanks. I think the tortoise shell-looking stuff is caused by minerals (maybe epidote?) that precipitated along a fracture surface (a small fault in this case). The striations are called "slickensides" and formed as one block slid past another.
10b4me, I'm not sure how thick the Conness Glacier is, and I don't know whether it is presently moving or not.
Greg
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Gene
climber
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If it's not moving and is shrinking, is it still a glacier?
Serious question.
Thanks,
g
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gstock
climber
Yosemite Valley
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Topic Author's Reply - Feb 5, 2013 - 06:07pm PT
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A glacier can be shrinking and still move downhill. However, movement is a defining feature of a glacier, so once it stops moving then it is arguably not a glacier anymore.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Greg: interesting stuff...thanks for posting this. Are you using GPS to monitor the locations of the stakes? If so, what is the shortest distance change that you can confidently detect from one year to the next? a few inches?
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gstock
climber
Yosemite Valley
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Topic Author's Reply - Feb 5, 2013 - 07:39pm PT
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We did use differential GPS but found that more reliable measurements were attainable with reflecting prisms and a laser rangefinder. The uncertainty on those measurements is about 10 cm over 500 m.
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Tobia
Social climber
Denial
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Greg: when I was teaching I used the NPS video of you measuring the glacier an describing the demise of it a few years back. I wish I could gather those kids around and let them see the now of it.
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Jon Beck
Trad climber
Oceanside
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Interesting but very disturbing stuff. Kinda like watching a train wreck.
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