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R. G. McGimsey

Publications and source records attributed to R. G. McGimsey.

17 recordsLinked to original sources
USGS2016

Geologic map of the Valdez D-1 and D-2 quadrangles (Mount Wrangell Volcano), Alaska

Geologic Note Mount Wrangell (elev. 4,317 m) is the youngest and only active volcano in the Oligocene to Holocene-aged Wrangell volcanic field that extends from beyond the Alaska-Yukon border northwest through the Wrangell Mountains to the Copper River Basin. The volcano is a very large (900 km 3 ) broad shield containing an ice-filled, nonexplosive, collapse caldera measuring 3.2 by 5.6 kilometers. Three known craters, the West, North, and East occur along the north and west margins of the caldera; the caldera is open to the southeast. The volcano is best exposed on its southwest flank (this map area) where a number of deep glaciated canyons cut through hundreds of meters of shield lava flows creating routes for younger, valley-filling lava flows. The shield extends north into the Gulkana A-1 quadrangle, northeast into the Nabesna A-6 quadrangle, and east into the McCarthy quadrangle where it is almost entirely covered by ice. The present extent of the Mount Wrangell shield showing the entire caldera and locations of the three summit craters is depicted in figure 1. Mount Wrangell was built rapidly beginning about 650 ka by the outpourings of hundreds of voluminous lava flows from a vent, or vents, apparently in the present summit area. By 200 ka to 300 ka, activity waned and only an occasional lava flow coursed down the glacially carved valleys radiating from the summit or flowed over the upper summit area above the heads of the glacial valleys. The youngest dated valley-fill lava flow is approximately 25,000 years old; one or two undated flows may be younger. In historical times there have been several reports of lava flows issuing from the summit area. The most reliable and convincing of these were two independent observations from Copper Center, Alaska on September 3, 1899 that described great earth movements (the 1899 Yakutat Bay earthquake) followed by an eruption at Mount Wrangell’s summit, consisting of vigorous ash emission and flowing lava on the volcano’s northwest flank. This eruptive activity apparently continued for several years after the earthquake, as a photo taken around 1901–02 shows a large part of Mount Wrangell’s summit blanketed by ash. During this study, no evidence of young lava flows in the region were found, although it is very possible that a small-volume flow could be entirely hidden by snow and ice in the 100 years since the event. However, abundant juvenile andesitic pumice was found on the upper Chetaslina Glacier, strongly supporting a very young pyroclastic eruption. In addition to the 1899–1902 eruptions there have been accounts of strong ash-producing activity on at least four different occasions: 1912, July 3, 1921, April 6, 1930, and February 20, 1982. Of these, the 1921 activity was the most spectacular, and possibly erupted from the northeast side of the summit caldera. Present activity is limited to fumaroles in North and West Crater at the summit, at the summit ridge near East Crater, and at two localities at an elevation of 3,657 m on the southwest flank. The summit fumaroles frequently give rise to visible steam plumes, and occasionally sporadic explosive phreatic activity in North and West Crater will put a thin dusting of ash on the summit ice. This study was directed toward Mount Wrangell volcano and the older Wrangell volcanic field rocks that underlie the volcano. These older lavas include the Chetaslina lavas (867 ka–1,650 ka) and a basaltic andesite–dacite center (1,590 ka–1,640 ka) whose source areas are not well defined. Older Paleozoic and Mesozoic sedimentary, igneous, and metamorphic rocks of the Wrangellia terrane underlie the entire Wrangell volcanic field.

Alaska↗
USGS2009

Diffuse gas emissions at the Ukinrek Maars, Alaska: Implications for magmatic degassing and volcanic monitoring

Diffuse CO2 efflux near the Ukinrek Maars, two small volcanic craters that formed in 1977 in a remote part of the Alaska Peninsula, was investigated using accumulation chamber measurements. High CO2 efflux, in many places exceeding 1000 g m−2 d−1, was found in conspicuous zones of plant damage or kill that cover 30,000–50,000 m2 in area. Total diffuse CO2 emission was estimated at 21–44 t d−1. Gas vents 3-km away at The Gas Rocks produce 0.5 t d−1 of CO2 that probably derives from the Ukinrek Maars basalt based on similar δ13C values (∼−6‰), 3He/4He ratios (5.9–7.2 RA), and CO2/3He ratios (1–2 × 109) in the two areas. A lower 3He/4He ratio (2.7 RA) and much higher CO2/3He ratio (9 × 1010) in gas from the nearest arc-front volcanic center (Mount Peulik/Ugashik) provide a useful comparison. The large diffuse CO2 emission at Ukinrek has important implications for magmatic degassing, subsurface gas transport, and local toxicity hazards. Gas–water–rock interactions play a major role in the location, magnitude and chemistry of the emissions.

Alaska↗
USGS2008

The 2005 catastrophic acid crater lake drainage, lahar, and acidic aerosol formation at Mount Chiginagak volcano, Alaska, USA: Field observations and preliminary water and vegetation chemistry results

A mass of snow and ice 400-m-wide and 105-m-thick began melting in the summit crater of Mount Chiginagak volcano sometime between November 2004 and early May 2005, presumably owing to increased heat flux from the hydrothermal system, or possibly from magma intrusion and degassing. In early May 2005, an estimated 3.8??10 6 m 3 of sulfurous, clay-rich debris and acidic water, with an accompanying acidic aerosol component, exited the crater through a tunnel at the base of a glacier that breaches the south crater rim. Over 27 km downstream, the acidic waters of the flood inundated an important salmon spawning drainage, acidifying Mother Goose Lake from surface to depth (approximately 0.5 km 3 in volume at a pH of 2.9 to 3.1), killing all aquatic life, and preventing the annual salmon run. Over 2 months later, crater lake water sampled 8 km downstream of the outlet after considerable dilution from glacial meltwater was a weak sulfuric acid solution (pH = 3.2, SO 4 = 504 mg/L, Cl = 53.6 mg/L, and F = 7.92 mg/L). The acid flood waters caused severe vegetation damage, including plant death and leaf kill along the flood path. The crater lake drainage was accompanied by an ambioructic flow of acidic aerosols that followed the flood path, contributing to defoliation and necrotic leaf damage to vegetation in a 29 km 2 area along and above affected streams, in areas to heights of over 150 m above stream level. Moss species killed in the event contained high levels of sulfur, indicating extremely elevated atmospheric sulfurcontent. The most abundant airborne phytotoxic constituent was likely sulfuric acid aerosols that were generated during the catastrophic partial crater lake drainage event. Two mechanisms of acidic aerosol formation are proposed: (1) generation of aerosol mist through turbulent flow of acidic water and (2) catastrophic gas exsolution. This previously undocumented phenomenon of simultaneous vegetationdamaging acidic aerosols accompanying drainage of an acidic crater lake has important implications for the study of hazards associated with active volcanic crater lakes. Copyright 2008 by the American Geophysical Union.

Geochemistry, Geophysics, Geosystems↗
USGS2008

Atmospheric contribution of gas emissions from Augustine volcano, Alaska during the 2006 eruption

Airborne surveillance of gas emissions from Augustine for SO 2 , CO 2 and H 2 S showed no evidence of anomalous degassing from 1990 through May 2005. By December 20, 2005, Augustine was degassing 660 td −1 of SO 2 , and ten times that by January 4, 2006. The highest SO 2 emission rate measured during the 2006 eruption was 8650 td −1 (March 1); for CO 2 , 13000 td −1 (March 9), and H 2 S, 8 td −1 (January 19). Thirty‐four SO 2 measurements were made from December 2005 through 2006, with 9 each for CO 2 and H 2 S. Augustine released 1 × 10 6 tonnes of CO 2 to the atmosphere during 2006, a level similar to the output of a medium‐sized natural gas‐fired power plant, and thus was not a significant contributor of greenhouse gas to the atmosphere compared to anthropogenic sources. Augustine released about 5 × 10 5 tonnes of SO 2 during 2006, similar to that released in 1976 and 1986.

Alaska↗
USGS2008

2005 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 eruptive activity or suspected volcanic activity at or near 16 volcanoes in Alaska during 2005, including the high profile precursory activity associated with the 2005–06 eruption of Augustine Volcano. AVO continues to participate in distributing information about eruptive activity on the Kamchatka Peninsula, Russia, and in the Kurile Islands of the Russian Far East, in conjunction with the Kamchatkan Volcanic Eruption Response Team (KVERT) and the Sakhalin Volcanic Eruption Response Team (SVERT), respectively. In 2005, AVO helped broadcast alerts about activity at 8 Russian volcanoes. The most serious hazard posed from volcanic eruptions in Alaska, Kamchatka, or the Kurile Islands is the placement of ash into the atmosphere at altitudes traversed by jet aircraft along the North Pacific and Russian Trans East air routes. AVO, KVERT, and SVERT work collaboratively with the National Weather Service, Federal Aviation Administration, and the Volcanic Ash Advisory Centers to provide timely warnings of volcanic eruptions and the production and movement of ash clouds.

Alaska, Kamchatka↗
USGS1998

Catalog of the historically active volcanoes of Alaska

Alaska hosts within its borders over 80 major volcanic centers that have erupted during Holocene time (< 10,000 years). At least 29 of these volcanic centers (table 1) had historical eruptions and 12 additional volcanic centers may have had historical eruptions. Historical in Alaska generally means the period since 1760 when explorers, travelers, and inhabitants kept written records. These 41 volcanic centers have been the source for >265 eruptions reported from Alaska volcanoes. With the exception of Wrangell volcano, all the centers are in, or near, the Aleutian volcanic arc, which extends 2500 km from Hayes volcano 145 km west of Anchorage in the Alaska-Aleutian Range to Buldir Island in the western Aleutian Islands (fig. 1). The volcanic arc, a subduction-related feature associated with underthrusting of the Pacific plate beneath the North American plate is divided between oceanic island arc and continental margin segments, the boundary occurring at about 165° W longitude (fig. 1). An additional 7 volcanic centers in the Aleutian arc (table 2; fig. 1 A) have active fumarole fields but no reported historical eruptions. This report discusses the location, physiography and structure, eruptive history, and geology of those volcanoes in Alaska that have experienced one or more eruptions that have been recorded in the written history (i.e., in historical time). It is part of the group of catalogs entitled Catalogue of Active Volcanoes of the World published beginning in 1951 under the auspices of the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI). A knowledge of the information contained in such catalogs aids in understanding the type and scale of activity that might be expected during a particular eruption, the hazards the eruption may pose, and even the prediction of eruptions. The catalog will thus be of value not only to the inhabitants of Alaska but to government agencies concerned with emergency response, air traffic operations, and weather, as well as to industry and scientists. The combination of the hazard posed by volcanic ash to jet aircraft and the heavy use of international air routes located parallel to, and on either side of, the Aleutian volcanic arc means that even remote volcanoes in Alaska now pose significant hazards to life and property. Although this report is concerned with historical eruptions from Alaskan volcanoes, other volcanoes in Alaska have erupted in the past 10,000 years and might therefore be expected to erupt again. Several Holocene volcanic centers in the Aleutian arc have no reported historical activity. Elsewhere in Alaska the Bering Sea basalt fields cover large areas of the Yukon Delta, Seward Peninsula, and several of the islands of the Bering Sea. Holocene centers also occur in the Wrangell Mountains and in isolated occurrences in the interior and southeastern Alaska. Eruptions from these centers have occurred within the past several hundred years but none were transcribed in the written record. Moodie and others (1992), however, report oral traditions among the Northern Athapaskan Indians of the southwestern Yukon Territory that may record the second and younger deposition of the White River Ash circa A.D. 720. This lobe of the White River Ash was deposited during the paroxysmal eruption of Churchill volcano in the Wrangell Mountains of eastcentral Alaska (McGimsey and others, 1992; Richter and others, 1995).

Alaska↗
USGS1996

A catastrophic flood caused by drainage of a caldera lake at Aniakchak Volcano, Alaska, and implications for volcanic hazards assessment

Aniakchak caldera, located on the Alaska Peninsula of southwest Alaska, formerly contained a large lake (estimated volume 3.7 × 10 9 m 3 ) that rapidly drained as a result of failure of the caldera rim sometime after ca. 3400 yr B.P. The peak discharge of the resulting flood was estimated using three methods: (1) flow-competence equations, (2) step-backwater modeling, and (3) a dam-break model. The results of the dam-break model indicate that the peak discharge at the breach in the caldera rim was at least 7.7 × 10 4 m 3 s −1 , and the maximum possible discharge was ≈1.1 × 10 6 m 3 s −1 . Flow-competence estimates of discharge, based on the largest boulders transported by the flood, indicate that the peak discharge values, which were a few kilometers downstream of the breach, ranged from 6.4 × 10 5 to 4.8 × 10 6 m 3 s −1 . Similar but less variable results were obtained by step-backwater modeling. Finally, discharge estimates based on regression equations relating peak discharge to the volume and depth of the impounded water, although limited by constraining assumptions, provide results within the range of values determined by the other methods. The discovery and documentation of a flood, caused by the failure of the caldera rim at Aniakchak caldera, underscore the significance and associated hydrologic hazards of potential large floods at other lake-filled calderas.

Geological Society of America Bulletin↗
USGS1994

Emission rates of sulfur dioxide and carbon dioxide from Redoubt Volcano, Alaska during the 1989-1990 eruptions

Airborne measurements of sulfur dioxide emission rates in the gas plume emitted from fumaroles in the summit crater of Redoubt Volcano were started on March 20, 1990 using the COSPEC method. During the latter half of the period of intermittent dome growth and destruction, between March 20 and mid-June 1990, sulfur dioxide emission rates ranged from approximately 1250 to 5850 t/d, rates notably higher than for other convergent-plate boundary volcanoes during periods of active dome growth. Emission rates following the end of dome growth from late June 1990 through May 1991 decreased steadily to less than 75 t/d. The largest mass of sulfur dioxide was released during the period of explosive vent clearing when explosive degassing on December 14-15 injected at least 175,000 ?? 50,000 tonnes of SO2 into the atmosphere. Following the explosive eruptions of December 1989, Redoubt Volcano entered a period of intermittent dome growth from late December 1989 to mid-June 1990 during which Redoubt emitted a total mass of SO2 ranging from 572,000 ?? 90,000 tonnes to 680,000 ?? 90,000 tonnes. From mid-June 1990 through May 1991, the volcano was in a state of posteruption degassing into the troposphere, producing approximately 183,000 ?? 50,000 tonnes of SO2. We estimate that Redoubt Volcano released a minimum mass of sulfur dioxide of approximately 930,000 tonnes. While COSPEC data were not obtained frequently enough to enable their use in eruption prediction, SO2 emission rates clearly indicated a consistent decline in emission rates between March through October 1990 and a continued low level of emission rates through the first half of 1991. Values from consecutive daily measurements of sulfur dioxide emission rates spanning the March 23, 1990 eruption decreased in the three days prior to eruption. That decrease was coincident with a several-fold increase in the frequency of shallow seismic events, suggesting partial sealing of the magma conduit to gas loss that resulted in pressurization of the shallow magma system and an increase in earthquake activity. Unlike the short-term SO2 decrease in March 1990, the long-term decrease of sulfur dioxide emission rates from March 1990 through May 1991 was coincident with low rates of seismic energy release and was interpreted to reflect gradual depressurization of the shallow magma reservoir. The long-term declines in seismic energy release and in SO2 emission rates led AVO scientists to conclude on April 19, 1991 that the potential for further eruptive activity from Redoubt Volcano had diminished, and on this basis, the level of concern color code for the volcano was changed from code yellow (Volcano is restless; earthquake activity is elevated; activity may include extrusion of lava) to code green (Volcano is in its normal 'dormant' state). ?? 1994.

Journal of Volcanology and Geothermal Research↗
USGS1994

Character, mass, distribution, and origin of tephra-fall deposits of the 1989-1990 eruption of redoubt volcano, south-central Alaska

The 1989-1990 eruption of Redoubt Volcano spawned about 20 areally significant tephra-fall deposits between December 14, 1989 and April 26, 1990. Tephra plumes rose to altitudes of 7 to more than 10 km and were carried mainly northward and eastward by prevailing winds, where they substantially impacted air travel, commerce, and other activities. In comparison to notable eruptions of the recent past, the Redoubt events produced a modest amount of tephra-fall deposits - 6 ?? 107 to 5 ?? 1010 kg for individual events and a total volume (dense-rock equivalent) of about 3-5 ?? 107 m3 of andesite and dacite. Two contrasting tephra types were generated by these events. Pumiceous tephra-fall deposits of December 14 and 15 were followed on December 16 and all later events by fine-grained lithic-crystal tephra deposits, much of which fell as particle aggregates. The change in the character of the tephra-fall deposits reflects their fundamentally different modes of origin. The pumiceous deposits were produced by magmatically driven explosions. The finegrained lithic-crystal deposits were generated by two processes. Hydrovolcanic vent explosions generated tephrafall deposits of December 16 and 19. Such explosions continued as a tephra source, but apparently with diminishing importance, during events of January and February. Ash clouds of lithic pyroclastic flows generated by collapse of actively growing lava domes probably contributed to tephra-fall deposits of all events from January 2 to April 26, and were the sole source of tephra fall for at least the last 4 deposits. ?? 1994.

Journal of Volcanology and Geothermal Research↗
USGS1981

The late-Neoglacial histories of the Agassiz and Jackson glaciers, Glacier National Park, Montana.

Twenty-one tree-ring stations, totaling 116 trees, were sampled at various localities within the forest trimlines fronting the Agassiz and Jackson glaciers, Glacier National Park, Montana. Tree ages within these zones became progressively younger from the region of the maximum late-Neoglacial position to the bases of the bedrock slopes on which these glaciers are now confined. The age of the oldest tree plus 15 yr was used to estimate the date of glacier withdrawal from a given station. It was found that both the Agassiz and Jackson glaciers began to retreat from their maximum late-Neoglacial positions about 1860. Hence, Matthes's (1940) estimate of glacial advances culminating about 1850 to 1855 for many glaciers in the western United States seems reasonable for the Glacier National Park region. Retreat rates, derived from the tree-ring data, appear to have been modest (<7 m yr -1 ) until about 1910 when they increased reaching more than 40 m yr -1 for the Agassiz Glacier between 1917 and 1926. Retreat rates after the late 1920s could not be monitored by tree-ring analysis as both glaciers had retreated onto bare bedrock dip slopes. However, from various literature descriptions and National Park Service records, both glaciers experienced rapid retreat (>100 m yr -1 ) from this time until 1932. In addition, while the Agassiz Glacier was monitored by the National Park Service (1932 to 1942) retreat continued at a rapid rate (>90 m yr -1 ). This period of rapid retreat corresponds with a period of above-average summer temperatures and decreased precipitation in the climatic record of the region. Since the mid-1940s the retreat rate of both glaciers has slowed markedly.

Montana↗