Geology topics

Christopher J. Nye

Publications and source records attributed to Christopher J. Nye.

12 recordsLinked to original sources

USGS2023

Geologic map of Okmok Volcano

The geologic map and description of map units presented here cover approximately 880 km2 of northeastern Umnak Island, Aleutian Islands, Alaska. This report focuses on Okmok Volcano and its eruptive products and updates the mid-20th-century geologic map of Byers (1959). Mapped deposits reflect the state of the volcano just prior to the 2008 eruption. Published information about other portions of Umnak Island geology, including Mount Recheshnoi and Mount Vsevidof, can be found in Byers (1959). The 2008 eruption and its deposits are described in Larsen and others (2009, 2013, 2015). Okmok Volcano is one of 54 historically active volcanoes in the Alaska–Aleutian volcanic arc that stretches across southern mainland Alaska and the Aleutian Islands (fig. 1; Wood and Kienle, 1990; Miller and others, 1998; Cameron and others, 2020). The highest point of the modern Okmok Caldera is along the caldera’s northern rim, 967 m in elevation, and formally named “Mount Okmok” (U.S. Board on Geographic Names, www.usgs.gov/core-science-systems/ngp/boardon-geographic-names/domestic-names). Okmok Volcano dominates the northeastern portion of Umnak Island, which is 100 km southwest of Unalaska/Dutch Harbor and 1,400 km southwest of Anchorage (figs. 1, 2). The Port of Dutch Harbor on Unalaska Island produces the highest volume of seafood for any port in the United States (see fisheries.noaa.gov/resource/document/fisheries-united-states-2018-report). Unalaska city and the Port of Dutch Harbor have been impacted by ash fall and drifting ash clouds from Okmok Volcano’s explosive eruptions as recently as 2008. Holocene and late Pleistocene volcanic rocks and deposits of Okmok Volcano rest upon glaciated Tertiary volcanic and sedimentary rocks (Byers, 1959). The first geologic mapping expedition to Okmok Volcano was by the U.S. Geological Survey (USGS) after the 1945 eruption, largely in response to concerns about volcanic hazards to U.S. military activities in the Aleutians Islands (Byers and others, 1947, 1959; Byers and Brannock, 1949; Byers, 1955, 1959, 1961). The State of Alaska conducted further mapping and geochemical studies as part of its geothermal exploration program in the 1980s (Nye, 1983; Nye and Reid, 1986; Motyka and others, 1993). Additional modern geological work focused on Okmok Volcano and the rest of Umnak Island to address the geochemistry and origin of primary Aleutian arc magmas and subduction zone mass recycling (Marsh, 1982; Brophy and Marsh, 1986; Nye and Reid, 1986; Myers and Marsh, 1987; Miller and others, 1992; Fournelle and others, 1994; Kay and Kay, 1994). In 1998, the Alaska Volcano Observatory (AVO) began a multi-year effort to expand geophysical monitoring in the central Aleutians Islands, including at Okmok Volcano. As part of this effort, AVO geologists from the University of Alaska Fairbanks Geophysical Institute (UAF/GI), the Alaska Division of Geological & Geophysical Surveys (DGGS), and USGS also began a renewed effort to document Okmok Volcano’s recent eruption products. The project started with reconnaissance fieldwork to document and sample products from the 1997 eruption within Okmok Caldera. This evolved into an effort to produce an updated geologic map of Okmok Volcano and gather more information about its eruptive history and hazards. Three significant eruptions occurred at Okmok Volcano in 1958, 1997, and 2008—after fieldwork had been conducted for the original 1:63,360-scale geologic map produced by Byers (1959)—resulting in new volcanic deposits not previously described. Okmok Volcano is one of the most frequently active volcanoes in the Aleutian volcanic arc. Seismic and geodetic monitoring indicate ongoing unrest at Okmok Volcano since at least 1997. Geodetic observations of inflation before and after the 1997 and 2008 eruptions indicate a nearly continuous input of new magma from a depth consistent with frequent eruptions of basalt and basaltic andesite magmas over the past 200 years (Larsen and others, 2013; Lu and others, 2000, 2003, 2005; Mann, 2002; Mann and others, 2002). To better understand the likelihood and character of future eruptions from Okmok Volcano, it is necessary to understand its past behavior, including eruptions since the first geologic map was published by Byers (1959).

Alaska↗

USGS2018

August 2008 eruption of Kasatochi volcano, Aleutian Islands, Alaska-resetting an Island Landscape

Kasatochi Island, the subaerial portion of a small volcano in the western Aleutian volcanic arc, erupted on 7-8 August 2008. Pyroclastic flows and surges swept the island repeatedly and buried most of it and the near-shore zone in decimeters to tens of meters of deposits. Several key seabird rookeries in taluses were rendered useless. The eruption lasted for about 24 hours and included two initial explosive pulses and pauses over a 6-hr period that produced ash-poor eruption clouds, a 10-hr period of continuous ash-rich emissions initiated by an explosive pulse and punctuated by two others, and a final 8-hr period of waning ash emissions. The deposits of the eruption include a basal muddy tephra that probably reflects initial eruptions through the shallow crater lake, a sequence of pumiceous and lithic-rich pyroclastic deposits produced by flow, surge, and fall processes during a period of energetic explosive eruption, and a fine-grained upper mantle of pyroclastic-fall and -surge deposits that probably reflects the waning eruptive stage as lake and ground water again gained access to the erupting magma. An eruption with similar impact on the island's environment had not occurred for at least several centuries. Since the 2008 eruption, the volcano has remained quiet other than emission of volcanic gases. Erosion and deposition are rapidly altering slopes and beaches. ?? 2010 Regents of the University of Colorado.

Alaska↗

USGS2017

Geology of Kasatochi Volcano, Aleutian Islands, Alaska

Kasatochi is a small, isolated island volcano in the center of the Aleutian Island chain. It consists of a roughly circular cone ~3 km in diameter with a lake-filled central crater that is 1.2 km in diameter and extends from the highest point on the island to sea level. The earliest unit recognized is a thick series of mid-Pleistocene glaciovolcanic deposits consisting of autobrecciated lava, lahars, and volumetrically minor lava masses that we believe to have been emplaced underneath a regional ice cap. This unit is unconformably overlain by several massive Holocene lavas, above which lies a thick sequence of latest- Holocene pyroclastic deposits likely deposited during the crater-forming eruption. The 2008 eruption enlarged the preexisting crater, and produced pyroclastic density currents, surges, and fall that blanketed the entire island except for steep, seaward-facing cliffs on the flanks and the crater wall. 2008 deposits initially extended the shoreline seaward by up to 500 m. Kasatochi lava and scoria are porphyritic basalt, basaltic andesite, and andesite, all of which bear trace-element evidence for prolonged crustal residence and equilibration with an amphibole-rich gabbroic residue. Lavas from individual effusive eruptions have limited compositional range, whereas juvenile scoriae from explosive eruptions span the majority of the compositional range of the entire volcano. 2008 pyroclastic deposits contain texturally diverse amphibole gabbro clasts and smaller, less abundant, plagioclase-free pyroxenitic and peridotitic cumulate inclusions. We infer that the gabbroic inclusions are from the margins of regions of crustal magma storage and evolution and that equilibration with the amphibole plays an important role in the evolution of mafic and intermediate magmas.

Alaska↗

USGS2014

Postglacial eruptive history, geochemistry, and recent seismicity of Aniakchak volcano, Alaska Peninsula

Aniakchak is a Pleistocene to Holocene composite volcano of the Alaska–Aleutian arc that suffered at least one caldera-forming eruption in postglacial time and last erupted in 1931. The oldest recognized postglacial eruption, Aniakchak I, produced andesite ignimbrite ca. 9,500–7,500 14 C yr B.P. Subsequently, a vent northeast of the summit issued dacite–rhyodacite magma ca. 7,000 14 C yr B.P. mainly as the Black Nose Pumice falls. The ca. 3,430 14 C yr B.P. Aniakchak II eruption produced rhyodacite plinian fall followed by rhyodacite and andesite ignimbrite extending ≥50 km to the Bering Sea and Pacific coasts and resulted in collapse of the 10-km-diameter caldera. Postcaldera vents are mainly on the caldera ring-fracture system. The earliest extruded small dacite domes into a deep caldera lake and a lava flow on the northwest flank. Three basaltic andesite–andesite tuff cones were constructed on the eastern caldera floor after catastrophic draining of the lake by ~200 m. Dacite–andesite magmas issued from Vent Mountain and Half Cone starting as early as ~1,000 years ago. Plinian eruption at Half Cone ~400 14 C yr B.P. yielded widespread dacite Pink and overlying andesite Brown Pumice fall deposits. Strombolian eruption of basaltic andesite built Blocky Cone after Half Cone and most Vent Mountain activity. The most recent eruption, in 1931, yielded dacite–rhyodacite tephra followed by relatively voluminous andesite tephra and ended with minor basaltic andesite. Current indications of an active magmatic system include high 3 He/ 4 He of CO 2 -rich gas at intracaldera Surprise Lake, InSAR pattern of caldera floor subsidence, and episodic seismicity. The majority of earthquakes are long-period (LP) events. Epicenters for 135 (2009–2012; M L ≤2.1) define a bow-tie pattern elongated parallel to plate convergence. Hypocenters identify events14–28 km below sea level (bsl), few events 7–14 km bsl beneath the caldera, and events <10 km bsl concentrated under Vent Mountain. Recent seismicity is consistent with long-lived mush in the quiet zone, from which magma escapes to be stored ephemerally to within ~2.5 km bsl. Future volcanic activity of Aniakchak could include hydromagmatic explosions, possibly followed by effusion or strombolian eruption of basaltic andesite to Plinian eruption of dacite. Another voluminous eruption, such as Aniakchak II, is considered unlikely in the near future.

Alaska↗

USGS2013

Andesites of the 2009 eruption of Redoubt Volcano, Alaska

Crystal-rich andesites that erupted from Redoubt Volcano in 2009 range from 57.5 to 62.5 wt.% SiO 2 and have phenocryst and phenocryst-melt relations consistent with staging in the upper crust. Early explosive products are low-silica andesites (LSA, < 58 wt.% SiO 2 ) that ascended from deeper crustal levels during or before the 6 months of precursory activity, but a broad subsequent succession to more evolved and cooler products, and predominantly effusive dome growth, are interpreted to result from progressive mobilization and mixing with differentiated magmas tapped from pre-2009 Redoubt intrusions at ~ 3–6 km depth. Initial explosions on March 23–28 ejected predominantly LSA with a uniform phenocryst assemblage of high-Al amphibole, ~ An 70 plagioclase, ortho- and clinopyroxene, FeTi oxides (890 to 960 °C), and traces of magmatic sulfide. Melt in the dominant microlite-poor LSA was compositionally uniform dacite (67–68 wt.% SiO 2 ) but ranged to rhyolite with greater microlite growth. Minor amounts of intermediate- to high-silica andesite (ISA, HSA; 59–62.5 wt.% SiO 2 ) also erupted during the early explosions and most carried rhyolitic melt (72–74 wt.% SiO 2 ). A lava dome grew following the initial tephra-producing events but was destroyed by an explosion on April 4. Ejecta from the April 4 explosion consists entirely of ISA and HSA, as does a subsequent lava dome that grew April 4–July 1; LSA was absent. Andesites from the April 4 event and from the final dome had pre-eruptive temperatures of 725–840 °C (FeTi oxides) and highly evolved matrix liquids (77–80 wt.% SiO 2 ), including in rare microlite-free pyroclasts. ISA has mixed populations of phenocrysts suggesting it is a hybrid between HSA and LSA. The last lavas from the 2009 eruption, effused May 1–July 1, are distinctly depleted in P 2 O 5 , consistent with low temperatures and high degrees of crystallization including apatite. Plagioclase–melt hygrometry and comparison to phase equilibrium experiments are consistent with pre-eruptive storage of all three magma types at 100–160 MPa (4–6 km depth), if they were close to H 2 O-saturation, coincident with the locus of shallow syn-eruptive seismicity. Deeper storage would be indicated if the magmas were CO 2 -rich. Relatively coarse-grained clinopyroxene-rich reaction rims on many LSA amphibole phenocrysts may result from slow ascent to, or storage at, depths shallow enough for the onset of appreciable H 2 O exsolution, consistent with pre-eruptive staging in the uppermost crust. We interpret that the 2009 LSA ascended from depth during the 8 or more months prior to the first eruption, but that the magma stalled and accumulated in the upper crust where its phenocryst rim and melt compositions were established. Ascent of LSA through stagnant mushy intrusions residual from earlier Redoubt activity mobilized differentiated magma pockets and interstitial liquids represented by HSA, and as LSA–HSA hybrids represented by ISA, that fed the subsequently erupted lava domes.

Alaska↗

USGS2011

The reawakening of Alaska's Augustine volcano

Augustine volcano, in south central Alaska, ended a 20-year period of repose on 11 January 2006 with 13 explosive eruptions in 20 days. Explosive activity shifted to a quieter effusion of lava in early February, forming a new summit lava dome and two short, blocky lava flows by late March (Figure 1). The eruption was heralded by eight months of increasing seismicity, deformation, gas emission, and small phreatic eruptions, the latter consisting of explosions of steam and debris caused by heating and expansion of groundwater due to an underlying heat source.

Alaska↗

USGS2010

The role of water in generating the calc-alkaline trend: New volatile data for aleutian magmas and a new tholeiitic index

The origin of tholeiitic (TH) versus calc-alkaline (CA) magmatic trends has long been debated. Part of the problem stems from the lack of a quantitative measure for the way in which a magma evolves. Recognizing that the salient feature in many TH–CA discrimination diagrams is enrichment in Fe during magma evolution, we have developed a quantitative index of Fe enrichment, the Tholeiitic Index (THI): THI = Fe 4 ·0 /Fe 8 ·0 , where Fe 4 ·0 is the average FeO* concentration of samples with 4 ± 1 wt % MgO, and Fe 8 ·0 is the average FeO* at 8 ± 1 wt % MgO. Magmas with THI > 1 have enriched in FeO* during differentiation from basalts to andesites and are tholeiitic; magmas with THI < 1 are calc-alkaline. Most subduction zone volcanism is CA, but to varying extents; the THI expresses the continuum of Fe enrichment observed in magmatic suites in all tectonic settings. To test various controls on the development of CA trends, we present new magmatic water measurements in melt inclusions from eight volcanoes from the Aleutian volcanic arc (Augustine, Emmons, Shishaldin, Akutan, Unalaska, Okmok, Seguam, and Korovin). Least degassed H 2 O contents vary from ∼2 wt % (Shishaldin) to >7 wt % (Augustine), spanning the global range in arc mafic magmas. Within the Aleutian data, H 2 O correlates negatively with THI, from strongly calc-alkaline (Augustine, THI = 0·65) to moderately tholeiitic (Shishaldin, THI = 1·16). The relationship between THI and magmatic water is maintained when data are included from additional arc volcanoes, back-arc basins, ocean islands, and mid-ocean ridge basalts (MORBs), supporting a dominant role of magmatic water in generating CA trends. An effective break between TH and CA trends occurs at ∼2 wt % H 2 O. Both pMELTs calculations and laboratory experiments demonstrate that the observed co-variation of H 2 O and THI in arcs can be generated by the effect of H 2 O on the suppression of plagioclase and the relative enhancement of Fe-oxides on the liquid line of descent. The full THI–H 2 O array requires an increase in fO 2 with H 2 O, from ≤FMQ (where FMQ is the fayalite–magnetite–quartz buffer) in MORB to ∼ΔFMQ +0·5 to +2 in arcs, consistent with inferences from measured Fe and S species in glasses and melt inclusions. A curve fit to the data, H 2 O (wt % ± 1·2) = exp[(1·26 – THI)/0·32], may provide a useful tool for estimating the H 2 O content of magmas that are inaccessible to melt inclusion study.

Journal of Petrology↗

USGS2007

Technical-information products for a National Volcano Early Warning System

Technical outreach — distinct from general-interest and K-12 educational outreach — for volcanic hazards is aimed at providing usable scientific information about potential or ongoing volcanic activity to public officials, businesses, and individuals in support of their response, preparedness, and mitigation efforts. Within the context of a National Volcano Early Warning System (NVEWS) (Ewert et al., 2005), technical outreach is a critical process, transferring the benefits of enhanced monitoring and hazards research to key constituents who have to initiate actions or make policy decisions to lessen the hazardous impact of volcanic activity. This report discusses recommendations of the Technical-Information Products Working Group convened in 2006 as part of the NVEWS planning process. The basic charge to the Working Group was to identify a web-based, volcanological "product line" for NVEWS to meet the specific hazard-information needs of technical users. Members of the Working Group were: Marianne Guffanti (Chair), USGS, Reston VA Steve Brantley, USGS, Hawaiian Volcano Observatory HI Peter Cervelli, USGS, Alaska Volcano Observatory, Anchorage AK Chris Nye, Division of Geological and Geophysical Surveys and Alaska Volcano Observatory, Fairbanks AK George Serafino, National Oceanic and Atmospheric Administration, Camp Springs MD Lee Siebert, Smithsonian Institution, Washington DC Dina Venezky, USGS, Volcano Hazards Team, Menlo Park CA Lisa Wald, USGS, Earthquake Hazards Program, Golden CO

Open-File Report↗

USGS2003

Preliminary volcano-hazard assessment for Great Sitkin Volcano, Alaska

Great Sitkin Volcano is a composite andesitic stratovolcano on Great Sitkin Island (51°05’ N latitude, 176°25’ W longitude), a small (14 x 16 km), circular volcanic island in the western Aleutian Islands of Alaska. Great Sitkin Island is located about 35 kilometers northeast of the community of Adak on Adak Island and 130 kilometers west of the community of Atka on Atka Island. Great Sitkin Volcano is an active volcano and has erupted at least eight times in the past 250 years (Miller and others, 1998). The most recent eruption in 1974 caused minor ash fall on the flanks of the volcano and resulted in the emplacement of a lava dome in the summit crater. The summit of the composite cone of Great Sitkin Volcano is 1,740 meters above sea level. The active crater is somewhat lower than the summit, and the highest point along its rim is about 1,460 meters above sea level. The crater is about 1,000 meters in diameter and is almost entirely filled by a lava dome emplaced in 1974. An area of active fumaroles, hot springs, and bubbling hot mud is present on the south flank of the volcano at the head of Big Fox Creek (see the map), and smaller ephemeral fumaroles and steam vents are present in the crater and around the crater rim. The flanking slopes of the volcano are gradual to steep and consist of variously weathered and vegetated blocky lava flows that formed during Pleistocene and Holocene eruptions. The modern edifice occupies a caldera structure that truncates an older sequence of lava flows and minor pyroclastic rocks on the east side of the volcano. The eastern sector of the volcano includes the remains of an ancestral volcano that was partially destroyed by a northwest-directed flank collapse. In winter, Great Sitkin Volcano is typically completely snow covered. Should explosive pyroclastic eruptions occur at this time, the snow would be a source of water for volcanic mudflows or lahars. In summer, much of the snowpack melts, leaving only a patchy distribution of snow on the volcano. Glacier ice is no longer present on the volcano or on other parts of Great Sitkin Island as previously reported by Simons and Mathewson (1955). Great Sitkin Island is presently uninhabited and is part of the Alaska Maritime National Wildlife Refuge, managed by the U.S. Fish and Wildlife Service.

Alaska↗

USGS2002

Preliminary volcano-hazard assessment for Kanaga Volcano, Alaska

Kanaga Volcano is a steep-sided, symmetrical, cone-shaped, 1307 meter high, andesitic stratovolcano on the north end of Kanaga Island (51°55’ N latitude, 177°10’ W longitude) in the western Aleutian Islands of Alaska. Kanaga Island is an elongated, low-relief (except for the volcano) island, located about 35 kilometers west of the community of Adak on Adak Island and is part of the Andreanof Islands Group of islands. Kanaga Volcano is one of the 41 historically active volcanoes in Alaska and has erupted numerous times in the past 11,000 years, including at least 10 eruptions in the past 250 years (Miller and others, 1998). The most recent eruption occurred in 1993-95 and caused minor ash fall on Adak Island and produced blocky aa lava flows that reached the sea on the northwest and west sides of the volcano (Neal and others, 1995). The summit of the volcano is characterized by a small, circular crater about 200 meters in diameter and 50-70 meters deep. Several active fumaroles are present in the crater and around the crater rim. The flanking slopes of the volcano are steep (20-30 degrees) and consist mainly of blocky, linear to spoonshaped lava flows that formed during eruptions of late Holocene age (about the past 3,000 years). The modern cone sits within a circular caldera structure that formed by large-scale collapse of a preexisting volcano. Evidence for eruptions of this preexisting volcano mainly consists of lava flows exposed along Kanaton Ridge, indicating that this former volcanic center was predominantly effusive in character. In winter (October-April), Kanaga Volcano may be covered by substantial amounts of snow that would be a source of water for lahars (volcanic mudflows). In summer, much of the snowpack melts, leaving only a patchy distribution of snow on the volcano. Glacier ice is not present on the volcano or on other parts of Kanaga Island. Kanaga Island is uninhabited and is part of the Alaska Maritime National Wildlife Refuge, managed by the U.S. Fish and Wildlife Service. The island is remote and often shrouded by clouds and fog. It can be reached only by boat, helicopter,or amphibiouslanding aircraft.

Alaska↗

USGS2001

Preliminary volcano-hazard assessment for Mount Spurr Volcano, Alaska

Mount Spurr volcano is an ice- and snow-covered stratovolcano complex located in the north-central Cook Inlet region about 100 kilometers west of Anchorage, Alaska. Mount Spurr volcano consists of a breached stratovolcano, a lava dome at the summit of Mount Spurr, and Crater Peak vent, a small stratocone on the south flank of Mount Spurr volcano. Historical eruptions of Crater Peak occurred in 1953 and 1992. These eruptions were relatively small but explosive, and they dispersed volcanic ash over areas of interior, south-central, and southeastern Alaska. Individual ash clouds produced by the 1992 eruption drifted east, north, and south. Within a few days of the eruption, the south-moving ash cloud was detected over the North Atlantic. Pyroclastic flows that descended the south flank of Crater Peak during both historical eruptions initiated volcanic-debris flows or lahars that formed temporary debris dams across the Chakachatna River, the principal drainage south of Crater Peak. Prehistoric eruptions of Crater Peak and Mount Spurr generated clouds of volcanic ash, pyroclastic flows, and lahars that extended to the volcano flanks and beyond. A flank collapse on the southeast side of Mount Spurr generated a large debris avalanche that flowed about 20 kilometers beyond the volcano into the Chakachatna River valley. The debris-avalanche deposit probably formed a large, temporary debris dam across the Chakachatna River. The distribution and thickness of volcanic-ash deposits from Mount Spurr volcano in the Cook Inlet region indicate that volcanic-ash clouds from most prehistoric eruptions were as voluminous as those produced by the 1953 and 1992 eruptions. Clouds of volcanic ash emitted from the active vent, Crater Peak, would be a major hazard to all aircraft using Ted Stevens Anchorage International Airport and other local airports and, depending on wind direction, could drift a considerable distance beyond the volcano. Ash fall from future eruptions could disrupt many types of economic and social activities, including oil and gas operations and shipping activities in the Cook Inlet area. Eruptions of Crater Peak could involve significant amounts of ice and snow that would lead to the formation of large lahars, formation of volcanic debris dams, and downstream flooding. The greatest hazards in order of importance are described below and shown on plate 1.

Alaska↗

USGS1990

The eruption of Redoubt Volcano, Alaska, December 14, 1989-August 31, 1990

No abstract available.

Alaska↗