o EXPLANATION VOLCANIC ASH FALLOUT AND DIRECTED BLAST
Transcript of o EXPLANATION VOLCANIC ASH FALLOUT AND DIRECTED BLAST
EXPLANATION VOLCANIC ASH FALLOUT AND DIRECTED BLAST
LAHAR HAZARDS
PYROCLASTIC-FLOW HAZARDS
DEBRIS-AVALANCHE HAZARDS
VOLCANIC GAS HAZARDS
VOLCANIC ASH HAZARDS
Areas likely to be inundated by lahars, lahar-runout flows, andfloods during eruptions of all sizes, but expecially during pyroclasticeruptions. Extent of inundation depends on the volume of the snow-pack and the duration of the eruption.
Areas that could be swept by pyroclastic flows to small to moderateeruptions from the present crater. Hazard boundaries correspond toH/L = 0.3 (inner zone) and H/L = 0.2 (outer zone).
Areas likely to be traversed by debris avalanches. Most likely aresmall-scale collapses of lava-flow fronts and spatter piles.
Areas where volcanic gas may be emitted.
Known pyroclastic-flow deposits.
Likely flow paths for pyroclastic flows.
Lava domes and possible vent areas that could be a source ofpyroclastic flows.
Thickness of <300-year-old pumice fall deposit, in centimeters.
Crater rim
Note: All areas of Great Sitkin Island are susceptible to ash fall.
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REGIONAL VOLCANIC ASH FALLOUT
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Akuyan Creek
Glacier Creek
Sitkin Creek
Sand Bay
Yoke Bay
BERING SEA
Middle Yoke Creek
Big Fox Creek
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Great Sitkin Volcano5,710 ft 1,740 m
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CONTOUR INTERVAL 1000 FEET
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Teapot Rock
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View of Great Sitkin Volcano from the north shore of Adak Island.
Present edifice
Crater Quaternary lava flows
Tertiary volcanic rocks
Great SitkinVolcano
Areas that could be affected by adirected blast similar to the blastgenerated by the 1980 eruption ofMt. St. Helens, Washington. Thisis a worst-case condition forGreat Sitkin Volcano.
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TanagaVolcano Bobroff
VolcanoKanagaVolcano
MountMoffett
MountAdagdak
KasatochiVolcano
KorovinVolcano
A n d r e a n o f I s l a n d s
BERING SEA
PACIFIC OCEANTanaga Island
Kanaga Island Adak Island
Great SitkinIsland
Atka Island
178o 176o
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Adak
Atka
Shaded area shows zonemost likely to receive ashfall during future eruptions.
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Approximate area that could beaffected by ash fallout during largeeruptions of Great Sitkin Volcano.Ash clouds will move with the prevailingwinds, which are generally westerly.
Shaded area shows zonemost likely to receive ashfall during future eruptionsof Great Sitkin Volcano.
TIMING OF VOLCANIC ACTIVITY EVIDENCE
<280 yr B.P.
550-700 yr B.P.
1150-1300 yr B.P.
34-3700 yr B.P.
3600-4000 yr B.P.
5900-6600 yr B.P.
7300-7600 yr B.P.
8400-8900 yr B.P.
>9500 yr B.P.
Lahar deposits in Sitkin and Akuyan Creek valleysPyroclastic-flow deposits in Glacier Creek valleyPumice lapilli tephra deposits
Lahar deposits in Sitkin Creek valleyPumice lapilli tephra deposits
Pumice lapilli tephra depositsLahar deposits in Sitkin Creek valley
Pumice lapilli tephra deposit (Sandwich ash?)
Pumice lapilli tephra deposit
Pumice lapilli tephra deposit
Pumice and lithic lapilli tephra deposit (Main ash?)
Lahar deposits in Sitkin Creek valley
Pumice lapilli tephra depositsLahar deposits in Sitkin Creek valley
Pumiceous pyroclastic-flow deposits north of Sitkin Creek valley
HOLOCENE ERUPTIONS
U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY
PRELIMINARY VOLCANO-HAZARD ASSESSMENT FOR GREAT SITKIN VOLCANO, ALASKAby
Christopher F. Waythomas, Thomas P. Miller, and Christopher J. Nye2003
OPEN-FILE REPORT 03-112PLATE 1
USG
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Volcano Observatory