Glacier Peak, USA

Image © USGS. Photo taken on August 2, 2007, by Jim Vallance.

Glacier Peak Earthquakes	Glacier Peak Seismograms
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Glacier Peak is the most remote of the five active volcanoes in Washington State. It is not prominently visible from any major population center, and so its attractions, as well as its hazards, tend to be over-looked. Yet since the end of the last ice age, Glacier Peak has produced some of the largest and most explosive eruptions in the state. During this time period, Glacier Peak has erupted multiple times during at least six separate episodes, most recently about 300 years ago. …

The stunning snow-capped volcanoes of Washington State have long been recognized by Native Americans in their language and legends, and they immediately caught the eyes of U.S. and European explorers in the late 18th and early 19th centuries. By the 1790s, Mounts Baker, Rainier, and St. Helens were noted and named in the first written descriptions of the Columbia River and Puget Sound regions. In 1805 Lewis and Clark noted Mount Adams. By the mid-19th century each of these four volcanoes had their place on a published map.

Glacier Peak wasn’t known by settlers to be a volcano until the 1850s, when Native Americans mentioned to naturalist George Gibbs that “another smaller peak to the north of Mount Rainier once smoked.” Not until 1898 did Glacier Peak appear on a published map under its current name.

Glacier Peak lies only 70 miles northeast of Seattle — closer to that city than any volcano except Mount Rainier. But unlike Mount Rainier, it rises only a few thousand feet above neighboring peaks, and from coastal communities it appears merely as a high point along a snowy saw-toothed skyline. Yet Glacier Peak has been one of the most active and explosive of Washington’s volcanoes.

Since the continental ice sheets receded from the region, Glacier Peak has erupted repeatedly during at least six episodes. Two of these eruptions were among the largest in Washington during the past 15,000 years.

From: Mastin and Waitt, 2000, Glacier Peak — History and Hazards of a Cascade Volcano: USGS Fact Sheet 058-00

Glacier Peak (3,213 meters) is a small Cascade Range stratovolcano. Although its summit reaches greater then 3,000 meters above the surrounding valleys, the main cone of Glacier Peak is perched on a high ridge, and the volcanic pile is no more than 500-1,000 meters thick. More than a dozen glaciers occur on the flanks of the volcano, and unconsolidated pyroclastic deposits over 12,000 years old have been largely removed by glaciation. Lava flows locally cap ridges to the northeast of the volcano, indicating a topographic reversal, and glacial and fluvial downcutting of more than 2,000 meters has occurred since the earliest cone-building eruptions. While small basaltic flows and cones are found at several points around the flanks of Glacier Peak, the main edifice is largely dacite and andesite. Lava flows extend no more than a few kilometers from the summit.

From: Wood and Kienle, (eds.), 1990, Volcanoes of North America – United States and Canada: Cambridge University Press, p.156-158, Contribution by Jim Beget

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REPORT:
Postglacial volcanic deposits at Glacier Peak, Washington, and potential hazards from future eruptions; a preliminary report

— Beget, J.E., 1982,
Postglacial volcanic deposits at Glacier Peak, Washington, and potential hazards from future eruptions; a preliminary report: U.S. Geological Survey Open-File Report 82-830, 81p.

Abstract

Eruptions and other geologic events at Glacier Peak volcano in northern Washington have repeatedly affected areas near the volcano as well as areas far downwind and downstream. This report describes the evidence of this activity preserved in deposits on the west and east flanks of the volcano.

On the west side of Glacier Peak the oldest postglacial deposit is a large, clayey mudflow which traveled at least 35 km down the White Chuck River valley sometime after 14,000 years ago. Subsequent large explosive eruptions produced lahars and at least 10 pyroclastic-flow deposits, including a semiwelded vitric tuff in the White Chuck River valley. These deposits, known collectively as the White Chuck assemblage, form a valley fill which is locally preserved as far as 100 km downstream from the volcano in the Stillaguamish River valley. At least some of the assemblage is about 11,670-11,500 radiocarbon years old.

A small clayey lahar, containing reworked blocks of the vitric tuff, subsequently traveled at least 15 km down the White Chuck River. This lahar is overlain by lake sediments containing charred wood which is about 5,500 years old. A 150-m-thick assemblage of pyroclastic-flow deposits and lahars, called the Kennedy Creek assemblage, is in part about 5,500-5,100 radiocarbon years old. Lithic lahars from this assemblage extend at least 100 km downstream in the Skagit River drainage. The younger lahar assemblages, each containing at least three lahars and reaching at least 18 km downstream from Glacier Peak in the White Chuck River valley, are about 2,800 and 1,800 years old, respectively. These are postdated by a lahar containing abundant oxyhornblende dacite, which extends at least 30 km to the Sauk River. A still younger lahar assemblage that contains at least five lahars, and that also extends at least 30 km to the Sauk River, is older than a mature forest growing on its surface.

At least one lahar and a flood deposit form a low terrace at the confluence of the White Chuck and Sauk Rivers, and were deposited before 300 years ago, but more recently than about 1,800 years ago. Several small outburst floods, including one in 1975, have affected Kennedy and Baekos Creek and the upper White Chuck River in the last hundred years.

East of Glacier Peak the oldest postglacial deposits consist of ash-cloud deposits that underlie tephra erupted by Glacier Peak between 12,750 and 11,250 radiocarbon years ago. Although pyroclastic-flow deposits correlative with the ash-cloud deposits have not been recognized, late Pleistocene pumiceous lahars extend at least 50 km downstream in the Suiattle River valley. A younger clayey mudflow extends at least 6 km down Dusty Creek. This lahar is overlain by deposits of lithic pyroclastic flows and lahars that form the Dusty assemblage. This assemblage is at least 300 m thick in the upper valleys of Dusty and Chocolate Creeks, and contains more than 10 km3 of lithic debris. Lahars derived from the Dusty assemblage extend at least 100 km down the Skagit River valley from Glacier Peak. This assemblage is younger than tephra layer 0 from Mount Mazama, and older than tephra layer Yn from Mount St. Helens, and thus was formed between about 7,000 and 3,400 years ago. The Dusty assemblage may have been formed at the same time as the Kennedy Creek assemblage.

A 1O0-m-thick assemblage of pyroclastic flows and lahars preserved in the Chocolate Creek valley is about 1,800 radiocarbon years old. A clayey lahar in the upper Chocolate Creek valley extended at least 2 km downvalley after 1,800 years ago, but before pyroclastic flows and lahars were deposited in upper Chocolate Creek 1,100 radiocarbon years ago. Several clayey lahars in the Dusty Creek valley east of Glacier Peak are also about 1,100 years old. A lahar in the valley of Dusty Creek, which contains rare prismatically jointed blocks of vesiculated dacite, and a white ash that is locally as much as 50 cm thick may be the products of small pyroclastic eruptions at Glacier Peak about 200-300 years ago.

Tephra deposits from past eruptions of Glacier Peak are mostly confined to the east side of the volcano. At least nine separate tephra layers were produced between 12,500 and 11,250 years ago. Two of these eruptions each produced about 2 km3 of ejecta. Tephra eruptions of much smaller volume occurred between 6,900 and 5,500 years ago, between 3,450 and 200 years ago, and between 316 and 90 years ago.

Future eruptions at Glacier Peak similar to those of postglacial time could affect people and property downstream and downwind from the volcano. Pyroclastic flows and lahars would affect valleys near the volcano. Lahars and floods could affect areas at low elevation along valley floors and in the Puget Lowland west of the volcano. Tephra from future eruptions will probably fall primarily east of Glacier Peak because of prevailing westerly winds.

The present
So, what is happening currently at Glacier Peak? According to the earthquake reports for the area not much you might think as the last recorded activity is in 2007. Is this the case however? Well possibly not has to be the answer. The seismograph station on Glacier Peak is the only one, and the next is some way away. To detect an earthquake using automated, and indeed manual, systems required 3 stations to be certain of an event. The problem here is that with only one station the seismicity is going to have to be very apparent before being detected automatically, and manual detection may or may not happen as this is always a noisy station anyway.

If you look at the seismograms page, then under the 1st November 2011 is my analysis of what I could ‘hear’ after converting the waveform to a sound file which I find easier to use. What became immediately obvious was that there is seismic activity. It may be small and may prove to be short lived, but it is there. Some of this does not even show on the seismogram over the noise and ice pops and wind, but I can hear the distinct earthquake double tap of the P and S waves that mark a local quake clearly for me.

This needs to be watched and for the time being it looks as if enthusiastic amateurs may hold the key as the seismologists cannot do everything and do not seem concerned at what they determine as wind and ice. They are wrong however. There are earthquakes in there as well.