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Robert G. McGimsey

Publications and source records attributed to Robert G. McGimsey.

At least 37 records · Page 2Linked to original sources
USGS2010

Emission of SO 2 , CO 2 , and H 2 S from Augustine Volcano, 2002-2008: Chapter 26 in The 2006 eruption of Augustine Volcano, Alaska

Airborne surveillance of gas emissions from Augustine Volcano and other Cook Inlet volcanoes began in 1990 to identify baseline emission levels during noneruptive conditions. Gas measurements at Augustine for SO 2 , CO 2 , and H 2 S showed essentially no evidence of anomalous degassing through spring 2005. Neither did a measurement on May 10, 2005, right after the onset of low level seismicity and inflation. The following measurement, on December 20, 2005, showed Augustine to be degassing about 600 metric tons per day (t/d) of SO 2 , and by January 4, 2006, only 7 days before the first explosive event, SO 2 emissions had climbed to ten times that amount. Maximum emission rates measured during the subsequent eruption were: 8,930 t/d SO 2 (February 24, 2006), 1,800 t/d CO 2 (March 9, 2006), and 4.3 t/d H 2 S (January 19, 2006). In total, 45 measurements for SO 2 were made from December 2005 through the end of 2008, with 19 each for CO 2 and H 2 S during the same period. Molar CO 2 /SO 2 ratios averaged about 1.6. In general, SO 2 emissions appeared to increase during inflation of the volcanic edifice, whereas CO 2 emissions were at their highest during the period of deflation associated with the vigorous effusive phase of the eruption in March. High SO 2 was probably associated with degassing of shallow magma, whereas high CO 2 likely reflected deep (>4 km) magma recharge of the sub-volcanic plumbing system, For the 2005–6 period, the volcano released a total of about 1.5×10 6 tons of CO 2 to the atmosphere, a level similar to the annual output of a medium-sized natural-gas-fired powerplant. Augustine also emitted about 8×10 5 tons of SO 2 , similar to that produced by the 1976 and 1986 eruptions of the volcano.

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USGS2010

Timing, distribution, and volume of proximal products of the 2006 eruption of Augustine Volcano: Chapter 8 in The 2006 eruption of Augustine Volcano, Alaska

During and after the 2006 eruption of Augustine Volcano, we compiled a geologic map and chronology of new lava and flowage deposits using observational flights, oblique and aerial photography, infrared imaging, satellite data, and field investigations. After approximately 6 months of precursory activity, the explosive phase of the eruption commenced with two explosions on January 11, 2006 (events 1 and 2) that produced snow-rich avalanches; little or no juvenile magma was erupted. Seismicity suggests that a small lava dome may have extruded on January 12, but, if so, it was subsequently destroyed. A series of six explosions on January 13–14 (events 3–8) produced widespread but thin (0–30 cm) pyroclastic-current deposits on the upper flanks above 300 m altitude and lobate, 0.5- to 2-m-thick pyroclastic flows that traveled down most flanks of the volcano. Between January 14 and 17, a smooth lava lobe formed in the east half of the roughly 400-m-wide summit crater and was only partially covered by later deposits. An explosion on January 17 (event 9) opened a crater in the new lava dome and produced a ballistic fall deposit and pyroclastic flow on the southwest flank. During the interval from January 17 to 27, a rubbly lava dome effused. On January 27, explosive event 10 generated a pyroclastic current that left a deposit, rich in dense clasts, on the north-northwest flank. Immediately following the pyroclastic current, a voluminous 4.7-km-long pyroclastic flow swept down the north flank. Three more explosive blasts on January 27 and 28 produced unknown but likely minor on-island deposits. The cumulative volume of erupted material from the explosive phase, including domes, flows, and fall deposits (Wallace and others, this volume), was 30×10 6 m 3 dense-rock equivalent (DRE). The continuous phase of the eruption (January 28 through February 10) began with a 4-day period of nearly continuous block-and-ash flows, which deposited small individual flow lobes that cumulatively formed fans to the north and northeast of the summit. A single larger pyroclastic flow on January 30 formed a braided deposit on the northwest flank. Roughly 9×10 6 m 3 (DRE) of magma erupted during this period. Around February 2, the magma flux rate waned and a northward lava flow effused and reached a length of approximately 900 m by February 10. Approximately 11×10 6 m 3 (DRE) of magma erupted during the second half of the continuous phase. After a 23-day hiatus, lava effusion recommenced in early March (the effusive phase) and was accompanied by frequent (but volumetrically minor) block-and-ash flows. From March 7 to 14, extrusion increased markedly; two blocky lava-flow lobes, each tens of meters thick, moved down the north and northeast flank of the volcano; and a new summit lava dome grew to be ~70 m taller than the pre-2006 summit. This phase produced 26×10 6 m 3 (DRE) of lava. Active effusion had ceased about March 16, but, in April and May, three gravitational collapses from the west margin of the north lava flow produced additional block-and-ash flows. The basic sequence of the 2006 eruption closely matches that of eruptions in 1976 and 1986.

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USGS2010

Timing, distribution, and character of tephra fall from the 2005-2006 eruption of Augustine Volcano: Chaper 9 in The 2006 eruption of Augustine Volcano

The 2005–6 eruption of Augustine Volcano produced tephra-fall deposits during each of four eruptive phases. Late in the precursory phase (December 2005), small phreatic explosions produced small-volume, localized, mostly nonjuvenile tephra. The greatest volume of tephra was produced during the explosive phase (January 11–28, 2006) when 13 discrete Vulcanian explosions generated ash plumes between 4 and 14 km above mean sea level (asl). A succession of juvenile tephra with compositions from low-silica to high-silica andesite is consistent with the eruption of two distinct magmas, represented also by a low-silica andesite lava dome (January 13–16) followed by a high-silica andesite lave dome (January 17–27). On-island deposits of lapilli to coarse ash originated from discrete vent explosions, whereas fine-grained, massive deposits were elutriated from pyroclastic flows and rock falls. During the continuous phase (January 28–February 10, 2006), steady growth and subsequent collapses of a high-silica andesite lava dome caused continuous low-level ash emissions and resulting fine elutriate ash deposits. The emplacement of a summit lava dome and lava flows of low-silica andesite during the effusive phase (March 3–16, 2006) resulted in localized, fine-grained elutriated ash deposits from small block-and-ash flows off the steep-sided lava flows. Mixing of two end-member magmas (low-silica and highsilica andesite) is evidenced by the overall similarities between tephra-fall and contemporaneous lava-dome and flow lithologies and by the chemical heterogeneity of matrix glass compositions of coarse lapilli and glass shards in the ash-size fraction throughout the 2005–6 eruption. A total mass of 2.2×10 10 kg of tephra fell (bulk volume of 2.2×10 7 m 3 and DRE volume of 8.5×10 6 m 3 ) during the explosive phase, as calculated by extrapolation of mass data from a single Vulcanian blast on January 17. Total tephra-fall volume for the 2005–6 eruption is about an order of magnitude smaller than other historical eruptions from Augustine Volcano. Ash plumes of short duration and small volume caused no more than minor amounts (≤1 mm) of ash to fall on villages and towns in the lower Cook Inlet region, and thus little hazard was posed to local communities. The bulk of the ash fell into Cook Inlet. Monitoring by the Alaska Volcano Observatory during the eruption helped to prevent hazardous encounters of ash and aircraft.

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USGS2008

2006 volcanic activity in Alaska, Kamchatka, and the Kurile Islands: Summary of events and response of the Alaska Volcano Observatory

The Alaska Volcano Observatory (AVO) responded to eruptions, possible eruptions, and volcanic unrest at or near nine separate volcanic centers in Alaska during 2006. A significant explosive eruption at Augustine Volcano in Cook Inlet marked the first eruption within several hundred kilometers of principal population centers in Alaska since 1992. Glaciated Fourpeaked Mountain, a volcano thought to have been inactive in the Holocene, produced a phreatic eruption in the fall of 2006 and continued to emit copious amounts of volcanic gas into 2007. AVO staff also participated in hazard communication and monitoring of multiple eruptions at seven volcanoes in Russia as part of its collaborative role in the Kamchatka and Sakhalin Volcanic Eruption Response Teams.

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USGS2007

Preliminary volcano-hazard assessment for the Tanaga volcanic cluster, Tanaga Island, Alaska

Summary of Volcano Hazards at Tanaga Volcanic Cluster The Tanaga volcanic cluster lies on the northwest part of Tanaga Island, about 100 kilometers west of Adak, Alaska, and 2,025 kilometers southwest of Anchorage, Alaska. The cluster consists of three volcanoes-from west to east, they are Sajaka, Tanaga, and Takawangha. All three volcanoes have erupted in the last 1,000 years, producing lava flows and tephra (ash) deposits. A much less frequent, but potentially more hazardous phenomenon, is volcanic edifice collapse into the sea, which likely happens only on a timescale of every few thousands of years, at most. Parts of the volcanic bedrock near Takawangha have been altered by hydrothermal activity and are prone to slope failure, but such events only present a local hazard. Given the volcanic cluster's remote location, the primary hazard from the Tanaga volcanoes is airborne ash that could affect aircraft. In this report, we summarize the major volcanic hazards associated with the Tanaga volcanic cluster.

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USGS2006

Geothermal disruption of summit glaciers at Mount Spurr Volcano, 2004-6: An unusual manifestation of volcanic unrest

Mount Spurr, a 3,374-m-high stratovolcano in the Cook Inlet region of Alaska, showed signs of volcanic unrest beginning in 2004 and lasting through 2006. These signs included increases in heat flow, seismicity, and gas flux, which we interpret as the results of a magmatic intrusion in mid-2004. In response, debris-laden meltwater beneath the glacier in Mount Spurr's geothermally active summit basin accumulated as the overlying snow and ice melted. As heat output increased, the icecap subsided into a growing cavity over a meltwater lake, similar to that observed during subglacial volcanic activity in Iceland. An ice plug collapsed into the lake sometime between June 20 and July 8, 2004, forming an ice cauldron that continued to grow in diameter during 2004 and 2005. A freefall of ice and snow into the lake likely caused a mixture of water and debris to be displaced rapidly upward and outward along preexisting englacial and, possibly, subglacial pathways leading away and downslope from the summit basin. Where these pathways intersected crevasses or other weak points in the sloping icefield, the mixture debouched onto the surface, producing dark, fluid debris flows. In summer 2004, the occurrence of two sets of debris flows separated in time by as long as a week suggests two pulses of summit ice collapse, each producing a surge of water and debris from the lake. A single debris flow was also emplaced on May 2, 2005. This event, which was captured by a Web camera, occurred simultaneously with a lake-level drop of ~15 m. To the east of the ice cauldron, a spillway that fed the debris flows has apparently maintained a relatively constant lake level for months at a time. Aerial photographs show that the spillway is in the direction of a breach in the summit crater. Melting of snow and ice at the summit has continued through 2006, with a total meltwater volume of ~5.4 million m3 as of March 2006.

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USGS2005

2001 volcanic activity in Alaska and Kamchatka: Summary of events and response of the Alaska Volcano Observatory

The Alaska Volcano Observatory (AVO) monitors the more than 40 historically active volcanoes of the Aleutian Arc. Of these, 22 are monitored with short-period seismic instrument networks as of the end of 2001. The AVO core monitoring program also includes daily analysis of satellite imagery, observation overflights, compilation of pilot reports and reports from local residents and mariners. In 2001, AVO responded to eruptive activity or suspected volcanic activity at or near 8 volcanic centers; Snowy and Kukak of the Kamai Group, Pavlof, Frosty, Shishaldin, Makushin, Okmok, Cleveland, and Great Sitkin volcanoes. In addition to responding to eruptive activity at Alaskan volcanoes, AVO assisted in the dissemination of information for the Kamchatka Volcanic Eruption Response Team (KVERT) regarding the 2001 activity of 5 Russian volcanoes—Sheveluch, Klyuchevskoy, Bezymianny, Karymsky, and Avachinsky volcanoes. Due to prevailing wind directions, erupting Kamchatkan and Alaskan volcanoes pose a serious threat to aircraft in the North Pacific.

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USGS2005

2003 volcanic activity in Alaska and Kamchatka: Summary of events and response of the Alaska Volcano Observatory

The Alaska Volcano Observatory (AVO) monitors the more than 40 historically active volcanoes of the Aleutian Arc. Of these, 24 were considered monitored in real time with short-period seismic instrument networks as of the end of 2003. The AVO core monitoring program also includes daily analysis of satellite imagery, observation over flights, and compilation of pilot reports and reports from local residents and mariners. In 2003, AVO responded to eruptive activity or suspected volcanic activity at or near 10 volcanic centers: Wrangell, Redoubt, Iliamna, Augustine, Mageik, Veniaminof, Pavlof, Emmons Lake (Hague), Shishaldin, and Akutan volcanoes. In addition to responding to eruptive activity at Alaska volcanoes, AVO assisted in the dissemination of information for the Kamchatka Volcanic Eruption Response Team (KVERT) about the 2003 activity of 6 Russian volcanoes: Sheveluch, Klyuchevskoy, Bezymianny, Karymsky, Alaid, and Chikurachki volcanoes. Due to prevailing wind directions, erupting Kamchatkan, Kurile Island, and Alaskan volcanoes pose a serious potential threat to aircraft in the North Pacific.

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USGS2005

Argon geochronology of late Pleistocene to Holocene Westdahl volcano, Unimak Island, Alaska

High-precision 40Ar/39Ar geochronology of selected lavas from Westdahl Volcano places time constraints on several key prehistoric eruptive phases of this large active volcano. A dike cutting old pyroclastic-flow and associated lahar deposits from a precursor volcano yields an age of 1,654+/-11 k.y., dating this precursor volcano as older than early Pleistocene. A total of 11 geographically distributed lavas with ages ranging from 47+/-14 to 127+/-2 k.y. date construction of the Westdahl volcanic center. Lava flows cut by an apparent caldera-rim structure yielded ages of 81+/-5 and 121+/-8 k.y., placing a maximum date of 81 ka on caldera formation. Late Pleistocene and Holocene lavas fill the caldera, but most of them are obscured by the large summit icecap.

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USGS2004

The Alaska Volcano Observatory - Expanded monitoring of volcanoes yields results

Recent explosive eruptions at some of Alaska's 52 historically active volcanoes have significantly affected air traffic over the North Pacific, as well as Alaska's oil, power, and fishing industries and local communities. Since its founding in the late 1980s, the Alaska Volcano Observatory (AVO) has installed new monitoring networks and used satellite data to track activity at Alaska's volcanoes, providing timely warnings and monitoring of frequent eruptions to the aviation industry and the general public. To minimize impacts from future eruptions, scientists at AVO continue to assess volcano hazards and to expand monitoring networks.

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USGS2004

1999 Volcanic activity in Alaska and Kamchatka: Summary of events and response of the Alaska Volcano Observatory

The Alaska Volcano Observatory (AVO) monitors 41 historically active volcanoes along the Aleutian Arc. Twenty are seismically monitored and for the rest, the AVO monitoring program relies mainly on daily analysis of satellite images, pilot reports, and observations of local residents and ship's crews. In 1999, AVO responded to eruptive activity or suspect volcanic activity at 7 volcanic centers: Wrangell, Shrub mud volcano, Iliamna, Veniaminof, Pavlof, Shishaldin, and Vsevidof volcanoes. Of these, in 1999, AVO had real-time, continuously recording seismic networks at Iliamna, and Shishaldin. The phrase “suspect volcanic activity” (SVA), used to characterize several responses, is an eruption report or report of unusual activity that is subsequently determined to be normal or enhanced fumarolic activity, weather-related phenomena, or a non-volcanic event. In addition to responding to eruptive activity at Alaska volcanoes, AVO also disseminated information for the Kamchatkan Volcanic Eruption Response Team (KVERT) about the 1999 activity of four Russian volcanoes: Sheveluch, Klyuchevskoy, Bezimianny, and Karymsky volcanoes.

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USGS2002

Volcanoes of the Alaska Peninsula and Aleutian Islands, Alaska: selected photographs

This CD-ROM contains 97 digital images of volcanoes along the Aleutian volcanic arc in Alaska. Perspectives include distant aerial shots, ground views of volcanic products and processes, and dramatic views of eruptions in progress. Each image is stored as a .PCD file in five resolutions. Brief captions, a location map, and glossary are included.

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USGS2001

Volcanoes of the Wrangell Mountains and Cook Inlet region, Alaska: selected photographs

Alaska is home to more than 40 active volcanoes, many of which have erupted violently and repeatedly in the last 200 years. This CD-ROM contains 97 digitized color 35-mm images which represent a small fraction of thousands of photographs taken by Alaska Volcano Observatory scientists, other researchers, and private citizens. The photographs were selected to portray Alaska's volcanoes, to document recent eruptive activity, and to illustrate the range of volcanic phenomena observed in Alaska. These images are for use by the interested public, multimedia producers, desktop publishers, and the high-end printing industry. The digital images are stored in the 'images' folder and can be read across Macintosh, Windows, DOS, OS/2, SGI, and UNIX platforms with applications that can read JPG (JPEG - Joint Photographic Experts Group format) or PCD (Kodak's PhotoCD (YCC) format) files. Throughout this publication, the image numbers match among the file names, figure captions, thumbnail labels, and other references. Also included on this CD-ROM are Windows and Macintosh viewers and engines for keyword searches (Adobe Acrobat Reader with Search). At the time of this publication, Kodak's policy on the distribution of color-management files is still unresolved, and so none is included on this CD-ROM. However, using the Universal Ektachrome or Universal Kodachrome transforms found in your software will provide excellent color. In addition to PhotoCD (PCD) files, this CD-ROM contains large (14.2'x19.5') and small (4'x6') screen-resolution (72 dots per inch; dpi) images in JPEG format. These undergo downsizing and compression relative to the PhotoCD images.

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USGS2001

Areal distribution, thickness, mass, volume, and grain size of tephra-fall deposits from the 1992 eruptions of Crater Peak vent, Mt. Spurr Volcano, Alaska

The Crater Peak flank vent of Mount Spurr volcano erupted June 27, August 18, and September 16-17, 1992. The three eruptions were similar in intensity (vulcanian to subplinian eruption columns reaching up to 14 km Above Sea Level) and duration (3.5 to 4.0 hours) and produced tephra-fall deposits (12, 14, 15 x 10 6 m 3 Dense Rock Equivalent [DRE]) discernible up to 1,000 km downwind. The June 27 ash cloud traveled north over the rugged, ice- and snow-covered Alaska Range. The August 18 ash cloud was carried southeastward over Anchorage, across Prince William Sound, and down the southeastern shoreline of the Gulf of Alaska. The September 16-17 ash plume was directed eastward over the Talkeetna and Wrangell mountains and into the Yukon Territory of Canada. Over 50 mass-per-unit-area (MPUA) samples were collected for each of the latter two fall deposits at distances ranging from about 2 km to 370 km downwind from the volcano. Only 10 (mostly proximal) samples were collected for the June fall deposit due to inaccessible terrain and funding constraints. MPUA data were plotted and contoured (isomass lines) to graphically display the distribution of each fall deposit. For the August and September eruptions, fallout was concentrated along a narrow (30 to 50 km wide) belt. The fallout was most concentrated (100,000 to greater than 250,000 g/m 2 ) within about 80 km of the volcano. Secondary maxima occur at 200 km (2,620 g/m 2 ) and 300 km (4,659 g/m 2 ), respectively, down axis for the August and September deposits. The maxima contain bimodal grain size distributions (with peaks at 88.4 and 22.1 microns) indicating aggregation within the ash cloud. Combined tephra-volume for the 1992 Mount Spurr eruptions (41 x 10 6 m 3 DRE) is comparable to that (tephra-fall only) of the 1989-90 eruptions of nearby Redoubt volcano (31-49 x 10 6 m 3 DRE).

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