U.S. DEPARTMENT OF THE INTERIOR OPEN-FILE REPORT 03-112 U.S. GEOLOGICAL SURVEY PLATE 1 o o 176 30' 176 20' EXPLANATION VOLCANIC ASH FALLOUT AND DIRECTED BLAST LAHAR HAZARDS 178o 176o 174o BERING SEA Areas likely to be inundated by lahars, lahar-runout flows, and floods during eruptions of all sizes, but expecially during pyroclastic o BERING SEA Teapot Rock eruptions. Extent of inundation depends on the volume of the snow- 52 Areas that could be affected by a ? pack and the duration of the eruption. 30' directed blast similar to the blast generated by the 1980 eruption of ? Mt. St. Helens, Washington. This Korovin Great Sitkin Volcano is a worst-case condition for Volcano PYROCLASTIC-FLOW HAZARDS Great Sitkin Volcano. Kasatochi Atka Areas that could be swept by pyroclastic flows to small to moderate Volcano eruptions from the present crater. Hazard boundaries correspond to Mount Great Sitkin 4000 Adagdak Island 52o Sitkin Creek H/L = 0.3 (inner zone) and H/L = 0.2 (outer zone). Mount Atka Island 52o Tanaga Kanaga Moffett 05' Bobroff + Volcano Volcano Volcano Known pyroclastic-flow deposits. Adak Great Sitkin Volcano ? 5,710 ft 1,740 m ? Likely flow paths for pyroclastic flows. Shaded area shows zone most likely to receive ash 3000 Adak Island fall during future eruptions. Kanaga Island nds Lava domes and possible vent areas that could be a source of sla I Akuyan Creek Tanaga Island pyroclastic flows. 51o 30' PACIFIC OCEAN nof 2000 Andrea DEBRIS-AVALANCHE HAZARDS 0 10 20 30 40 50 MILES Areas likely to be traversed by debris avalanches. Most likely are 0 10 20 30 40 50 60 70 KILOMETERS small-scale collapses of lava-flow fronts and spatter piles. 1000 Glacier Creek VOLCANIC GAS HAZARDS REGIONAL VOLCANIC ASH FALLOUT 43 Middle Yoke Creek Areas where volcanic gas may be emitted. 30 VOLCANIC ASH HAZARDS 52o Yoke Bay 60 00' 26 Thickness of <300-year-old pumice fall deposit, in centimeters. Big Fox Creek Sand Bay Crater rim 26 0 5 MILES Note: All areas of Great Sitkin Island are susceptible to ash fall. 0 5 KILOMETERS CONTOUR INTERVAL 1000 FEET HOLOCENE ERUPTIONS TIMING OF VOLCANIC ACTIVITY EVIDENCE Lahar deposits in Sitkin and Akuyan Creek valleys <280 yr B.P. Pyroclastic-flow deposits in Glacier Creek valley Pumice lapilli tephra deposits Lahar deposits in Sitkin Creek valley 550-700 yr B.P. Crater Pumice lapilli tephra deposits Shaded area shows zone Quaternary lava flows most likely to receive ash Lahar deposits in Sitkin Creek valley fall during future eruptions Present edifice 1150-1300 yr B.P. of Great Sitkin Volcano. Tertiary volcanic rocks Pumice lapilli tephra deposits 34-3700 yr B.P. Pumice lapilli tephra deposit (Sandwich ash?) 3600-4000 yr B.P. Pumice lapilli tephra deposit 5900-6600 yr B.P. Pumice lapilli tephra deposit Approximate area that could be affected by ash fallout during large 7300-7600 yr B.P. Pumice and lithic lapilli tephra deposit (Main ash?) eruptions of Great Sitkin Volcano. Ash clouds will move with the prevailing Lahar deposits in Sitkin Creek valley winds, which are generally westerly. 8400-8900 yr B.P. Pumice lapilli tephra deposits Pumiceous pyroclastic-flow deposits north of Sitkin Creek valley View of Great Sitkin Volcano from the north shore of Adak Island. >9500 yr B.P. Lahar deposits in Sitkin Creek valley o O n a b c l s o e r V v PRELIMINARY VOLCANO-HAZARD ASSESSMENT FOR GREAT SITKIN VOLCANO, ALASKA a a t k o s r by a l y A Christopher F. Waythomas, Thomas P. Miller, and Christopher J. Nye U S S G G G 2003 S D - U A F / G I - A.