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Volcano Watch Weekly: 23 April 2009

Posted by feww on April 23, 2009

Volcanic Activity Report: 15 April – 21 April 2009

Source: Global Volcanism program (GVP) – SI/USGS Weekly Volcanic Activity Report

New activity/unrest:

  • Ebeko, Paramushir Island  (Russia)
  • Fernandina, Galápagos Islands  (Ecuador)
  • Kliuchevskoi, Central Kamchatka (Russia)
  • NW Rota-1, Mariana Islands (Central Pacific)
  • Pagan, Mariana Islands (Central Pacific)
  • Paluweh, Lesser Sunda Islands (Indonesia)

VoW: Shasta

Volcano: Mount Shasta
Location: Siskiyou County, California
Latitude: 41.40 N
Longitude: 122.18 W
Height: 4,317 Meters  (14,161 Feet)
Type: Stratovolcano
Composition: Silicic andesite to dacite
Source: USGS (Cascades Volcano Observatory)


Mount Shasta and Shastina, California. USGS Photograph taken by Lyn Topinka, 1984 .

From: Miller, 1980, Potential Hazards from Future Eruptions in the Vicinity of Mount Shasta Volcano, Northern California: USGS Bulletin 1503

Mount Shasta is located in the Cascade Range in northern California about 65 kilometers (40 miles) south of the Oregon-California border and about midway between the Pacific Coast and the Nevada border. One of the largest and highest of the Cascade volcanoes, snowclad Mount Shasta is near the southern end of the range that terminates near Lassen Peak. Mount Shasta is a massive compound stratovolcano composed of overlapping cones centered at four or more main vents; it was constructed during a period of more than 100,000 years. … Two of the main eruptive centers at Mount Shasta, the Shastina and Hotlum cones were constructed during Holocene time, which includes about the last 10,000 years.

For more information including eruptive history and probable future potential hazard see: Mount Shasta and Vicinity, California


The most voluminous of the Cascade volcanoes, northern California’s Mount Shasta is a massive compound stratovolcano composed of at least four main edifices constructed over a period of at least 590,000 years.
Roughly 46 cu km of an ancestral Shasta volcano was destroyed by one of Earth’s largest known Quaternary subaerial hummocky debris avalanches, which filled the Shasta River valley NW of the volcano about 350,000 year ago.  The Hotlum cone, forming the present summit, and the Shastina lava dome complex were constructed during the early Holocene, as was the SW flank Black Butte lava dome. Eruptions from these vents have produced pyroclastic flows and mudflows that affected areas as far as 20 km from the summit. Eruptions from Hotlum cone continued throughout the Holocene. Shasta’s only historical eruption was observed from the ship of the explorer La Perouse off the California coast in 1786.  Photo by Dave Wieprecht, 1995 (U.S. Geological Survey). Caption: GVP


The deposits of an exceptionally large debris avalanche extend from the base of Mount Shasta volcano northward across the floor of Shasta Valley in northern California. The debris-avalanche deposits underlie an area of about 675 square kilometers, and their estimated volume is at least 45 cubic kilometers. Radiometric limiting dates suggest that the debris avalanche occurred between about 300,000 and 380,000 years ago. Hundreds of mounds, hills, and ridges formed by the avalanche deposits are separated by flat areas that slope generally northward at about 5 meters per kilometer. The hills and ridges are formed by the block facies of the deposits, which includes masses of andesite lava tens to hundreds of meters across as well as stratigraphic successions of unconsolidated deposits of pyroclastic flows, lahars, air-fall tephra, and alluvium, which were carried intact within the debris avalanche. The northern terminus of the block facies is near Montague, at a distance of about 49 kilometers from the present summit of the volcano. The flat areas between hills and ridges are underlain by the matrix facies, which is an unsorted and unstratified mudflowlike deposit of sand, silt, clay, and rock fragments derived chiefly from the volcano. Boulders of volcanic rock from Mount Shasta are scattered along the west side of Shasta Valley and in the part of Shasta Valley that lies north of Montague, at heights of as much as 100 meters above the adjacent surface of the debris-avalanche deposits. The boulders represent a lag that was formed after the main body of the avalanche came to rest, when much of the still-fluid matrix facies drained away and flowed out of Shasta Valley down the Shasta River valley and into the Klamath River. About 300 years ago, three rockfall-debris avalanches occurred from domes at the Chaos Crags eruptive center near Lassen Peak. The Chaos Crags avalanches traveled as far as 4.3 kilometers from their source areas. USGS Photograph taken September 22, 1982, by Harry Glicken. Caption: CVO


Mount Shasta, California Debris Avalanche Deposit. Source: USGS – CVO

Ongoing Activity:


FEWW Volcanic Forecast:

(see: Sumatra’s Mt Kerinci Erupts )

1. The Loyalty – New Hebrides  Arc Collision. Intense volcanic activity should be expected throughout 2009 and beyond along the New Hebrides arc, the Vanatu region (also to the north to include Solomon Island and Santa Cruz Island), possibly continued along the New Hebrides Trench (to include Matthew and Hunter Island). Volcanoes that are located in the above-described area include:

  • Savo (Solomon Island)
  • Tinakula (Santa Cruz Island – SW Pacific)
  • Suretamatai
  • Motlav
  • Gaua
  • Mere Lava
  • Aoba
  • Ambrym
  • Lopevi
  • Kuwae
  • North Vate
  • Traitor’s Head
  • Yasur
  • Eastern Gemini Seamount
  • Matthew Island
  • Hunter Island

2. Pacific Plate subduction beneath the Okhotsk Plate. Subduction of the Pacific Plate beneath the Okhotsk Plate continues to create Intense volcanism. Starting 2009, however, a much greater than the average number of volcanoes located on the Kuril Islands island arc, Kamchatka volcanic arc and Japan trench to the south may erupt with renewed intensity.

Related Link and FEWW previous forecasts:

Posted in Chaiten, Galapagos Islands, Koryaksky, volcanic activity, volcanism | Tagged: , , , , | Leave a Comment »

 
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