Hi, all! Darryl Lloyd (http://www.longshadowphoto.com) sent out an e-mail to his list today about a debris avalanche on Mt. Adams. Here's part of his message:
...received an email from USGS seismologist, Bob Norris in Seattle, about a large avalanche on the SW side of Mt. Adams. It read in part:
"We recorded a large seismic signal from Mount Adams at 0742 PDT this morning. You can see it on the Mount Adams seismograph page:
http://www.pnsn.org/WEBICORDER/VOLC/ASR ... 80112.html
Seismically, it's about the size of the 1983 event."
Bob called it accurately. I just took the photo below (through smokey haze) and worked with it to bring out contrast. Looks like about a 2-mile-long debris avalanche of mostly rock, beginning near the 11,800 ft. level on the Avalanche Glacier headwall and ending at the base of the glacier at around 8,000 ft.
As Bob reported, it appears to be about the same size and location as the 1983 debris avalanche, although this one may have a greater percentage of rock. It's the largest event on Avalanche Glacier since late summer of 1997, when a 3-mile-long avalanche of mostly ice swept Avalanche Glacier.
I'll get better photos later today from the Trout Lake area.
Darryl Lloyd
Mt. Adams Debris Avalanche
Re: Mt. Adams Debris Avalanche
Sounds pretty cool. What a dramatic season over that way! I'm curious to see some more pictures.
Re: Mt. Adams Debris Avalanche
Another e-mail from Darryl:
From this foreshortened wide-angle photo taken by HC Tupper on
August 2nd, the slide appears to have started with a large ice
avalanche high on Avalanche Glacier, near the 11,500-ft. level.
White Salmon Glacier lies just to the west of the avalanche source
and is divided from Avalanche Glacier by a hogback ridge of snow and
ice.
I now think this two-mile-long avalanche consists of more ice ice
than rock, similar to the 1983 and 1997 avalanches.
Darryl
From this foreshortened wide-angle photo taken by HC Tupper on
August 2nd, the slide appears to have started with a large ice
avalanche high on Avalanche Glacier, near the 11,500-ft. level.
White Salmon Glacier lies just to the west of the avalanche source
and is divided from Avalanche Glacier by a hogback ridge of snow and
ice.
I now think this two-mile-long avalanche consists of more ice ice
than rock, similar to the 1983 and 1997 avalanches.
Darryl
- Attachments
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Re: Mt. Adams Debris Avalanche
Latest e-mail from Darryl:
This evening I galloped to viewpoints SW of Mt. Adams and got these shots of the August 1, 2008 avalanche.
On the morning of August 1st, 2008, a large section of Avalanche Glacier broke off near 11,400-ft. level and swept about 1.5 miles down the glacier and ended near the 8,200 ft. level. The initial ice mass that broke off is roughly 130 ft. thick (max.) by about 500 ft. wide and at least 600 ft. long. The avalanche scoured out rock at the base of the glacier as it fell.
The headwalls above Avalanche and White Salmon Glaciers consist of weak, hydrothermally altered rock and are the source of many debris avalanches and lahars. By far the largest was the great "Trout Lake Mudflow" around 6,000 years ago. USGS scientist, Jim Vallance at the CVO in Vancouver has done extensive research on these events on Mt. Adams.
http://vulcan.wr.usgs.gov/Volcanoes/Ada ... tract.html
This and the last two big debris avalanches in 1983 and 1997 occured during summers of unusually high winter snowpack. Avalanche Glacier is certainly well-named!
Darryl
This evening I galloped to viewpoints SW of Mt. Adams and got these shots of the August 1, 2008 avalanche.
On the morning of August 1st, 2008, a large section of Avalanche Glacier broke off near 11,400-ft. level and swept about 1.5 miles down the glacier and ended near the 8,200 ft. level. The initial ice mass that broke off is roughly 130 ft. thick (max.) by about 500 ft. wide and at least 600 ft. long. The avalanche scoured out rock at the base of the glacier as it fell.
The headwalls above Avalanche and White Salmon Glaciers consist of weak, hydrothermally altered rock and are the source of many debris avalanches and lahars. By far the largest was the great "Trout Lake Mudflow" around 6,000 years ago. USGS scientist, Jim Vallance at the CVO in Vancouver has done extensive research on these events on Mt. Adams.
http://vulcan.wr.usgs.gov/Volcanoes/Ada ... tract.html
This and the last two big debris avalanches in 1983 and 1997 occured during summers of unusually high winter snowpack. Avalanche Glacier is certainly well-named!
Darryl
- Attachments
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- SW face of Mt. Adams from gravel pit near Eckhart Point (8-6-08)
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- The last two photos were taken from FS Rd. 2360, a short distance above FS Rd. 23. (8-6-08)
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Re: Mt. Adams Debris Avalanche
Here's Michael Milstein's article in the Oregonian:
http://www.oregonlive.com/environment/i ... mount.html
Major avalanche reworks Mount Adams
by Michael Milstein, The Oregonian
Wednesday August 06, 2008, 2:59 PM
A two-mile-long avalanche of ice and rocks large enough to rattle seismometers has reworked the southwest face of Mount Adams.
The volcano is usually very quiet, with few of the tremors that occur occasionally at other Cascade volcanoes such as Mount Hood. So the seismic signal from Mount Adams on Aug. 1 stood out to Cynthia Gardner of the Cascades Volcano Observatory in Vancouver, who first noticed it.
"It is a very large signal at a volcano that has a very quiet background," she told The Oregonian on Wednesday.
She passed on her observations to researchers at the Pacific Northwest Seismic Network at the University of Washington. There, seismologist Robert Norris recognized it as the likely signature of a major avalanche or rockfall, Norris said.
He relayed the information to Darryl Lloyd, a Hood River photographer and longtime authority on the Mount Adams region. Lloyd reported back that indeed a major avalanche beginning at Avalanche Glacier had tumbled about two miles down the mountain.
The Avalanche Glacier area of the mountain is aptly named, as it has released major avalanches in the past. A rock-and-ice avalanche from the same area in August 1997 ran about three miles down the mountain. It contained an estimated 5 million cubic meters of material and was the largest avalanche in the Cascades since one on Mount Rainier in 1963, according to the Cascades Volcano Observatory.
The avalanche this month was not that big, Lloyd said. It was more akin to a 1983 avalanche from the same area.
Norris said one line of thinking for how the avalanches occur is that ice and snow piling up on the mountain eventually overwhelms the strength of the loose volcanic rock below it and both come tumbling down. All three of the known large avalanches from this area on Mount Adams have occurred in a summer following a winter of especially heavy snow, Norris and Lloyd noted.
"That weak substrate can only support so much ice," he said.
In the past avalanches, a large part of Avalanche Glacier has tumbled down, Norris said. Lloyd said it's not clear how much of the glacier remains.
Such avalanches are a major force in reshaping Cascade volcanoes between eruptions, Gardner said.
http://www.oregonlive.com/environment/i ... mount.html
Major avalanche reworks Mount Adams
by Michael Milstein, The Oregonian
Wednesday August 06, 2008, 2:59 PM
A two-mile-long avalanche of ice and rocks large enough to rattle seismometers has reworked the southwest face of Mount Adams.
The volcano is usually very quiet, with few of the tremors that occur occasionally at other Cascade volcanoes such as Mount Hood. So the seismic signal from Mount Adams on Aug. 1 stood out to Cynthia Gardner of the Cascades Volcano Observatory in Vancouver, who first noticed it.
"It is a very large signal at a volcano that has a very quiet background," she told The Oregonian on Wednesday.
She passed on her observations to researchers at the Pacific Northwest Seismic Network at the University of Washington. There, seismologist Robert Norris recognized it as the likely signature of a major avalanche or rockfall, Norris said.
He relayed the information to Darryl Lloyd, a Hood River photographer and longtime authority on the Mount Adams region. Lloyd reported back that indeed a major avalanche beginning at Avalanche Glacier had tumbled about two miles down the mountain.
The Avalanche Glacier area of the mountain is aptly named, as it has released major avalanches in the past. A rock-and-ice avalanche from the same area in August 1997 ran about three miles down the mountain. It contained an estimated 5 million cubic meters of material and was the largest avalanche in the Cascades since one on Mount Rainier in 1963, according to the Cascades Volcano Observatory.
The avalanche this month was not that big, Lloyd said. It was more akin to a 1983 avalanche from the same area.
Norris said one line of thinking for how the avalanches occur is that ice and snow piling up on the mountain eventually overwhelms the strength of the loose volcanic rock below it and both come tumbling down. All three of the known large avalanches from this area on Mount Adams have occurred in a summer following a winter of especially heavy snow, Norris and Lloyd noted.
"That weak substrate can only support so much ice," he said.
In the past avalanches, a large part of Avalanche Glacier has tumbled down, Norris said. Lloyd said it's not clear how much of the glacier remains.
Such avalanches are a major force in reshaping Cascade volcanoes between eruptions, Gardner said.