Alaska Open-file Report 144 Assessment of Thermal Springs Sites Aleutian Arc, Atka Island to Becherof Lake -- Preliminary Results and Evaluation

Motyka, R. J.; Moorman,; Liss, S. A.

doi:10.2172/897401

Cited by 3 publications

(4 citation statements)

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“…This is a typical coexistence of seismic parameters for gas-saturated rocks [31,32,38], as they behave as a sponge having very low bulk elastic parameters [39]. This hypothesis is supported by the existence of several hydrothermal fields in the caldera area [17], which match this anomaly of low Vp/Vs ratio. At greater depth, the relationships between the P and S wave parameters turn out to be opposite beneath the Kliuchef and the Atka Caldera, at 3 km depth, we observe a prominent high Vp, low Vs and very high Vp/Vs ratio, which is similar to the structure beneath Korovin at the same depth.…”

Section: Discussionmentioning

confidence: 61%

“…They are associated with steam vents, thermal springs, mud pots and small explosive crater lakes. The mean temperature of the geothermal reservoir beneath this area is 169 • C, which is the lowest among other sources on Atka [17]. Thermal areas on the southwestern slope of the Kliuchef volcano lie at higher elevation (600-1000 m a.s.l.…”

Section: Discussionmentioning

confidence: 82%

“…The highest thermal site of the Kliuchef volcano is located below the Milky River glacier, which covers the summit of the volcano. According to Motyka et al [17], all hot sources in northeastern Atka contain sulfate-rich chlorine-poor waters, which may indicate that shallow meteoric water is heated by deeper boiling hot-water system associated with the magma sources, releasing steam, hydrogen sulfide and other gases. However, they do not present an accurate estimate for the ratio between the deep and shallow fluid sources.…”

Section: Discussionmentioning

confidence: 99%

“…Another active volcano of the AVC, Mount Kliuchef (1460 m) is located within the caldera and is composed of basalt-to-dacite lava flows and pyroclasts [15,16]. The southern and western flanks of Kliuchef are presently marked by active thermal fields and hot springs (yellow fields in Figure 1c) [17]. Konia is another predominantly dacitic stratovolcano between Korovin and Kliuchef having a smaller size.…”

Section: Introductionmentioning

confidence: 99%

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Magma Chambers and Meteoric Fluid Flows Beneath the Atka Volcanic Complex (Aleutian Islands) Inferred from Local Earthquake Tomography

2020

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Atka is a subduction-related volcanic island located in the central part of Aleutian Arc. The northeastern part of this island forms the Atka Volcanic Complex (AVC), which is built as a relict shield volcano of a circular shape overlain by several active and extinct volcanic vents of different ages. During the past few decades, two active volcanoes within AVC—Korovin and Kliuchef—demonstrated mostly phreatic eruptions and intensive fumarolic activity. We have created the first tomographic model of the crust beneath AVC with the use of data of eight permanent stations of the Alaskan Volcanological Observatory operated in the time period from 2004 to 2017 that included arrival times of the P and S waves from local seismicity. Based on a series of checkerboard tests, we have demonstrated fair vertical and horizontal resolution of the model down to ~6 km depth. Beneath the Korovin and Kliuchef volcanoes, we have revealed two isolated anomalies of high Vp/Vs with values exceeding 2, which represent separate magma chambers that are responsible for magmatic eruptions of these two volcanoes. In shallow layers down to 2–3 km deep, we observe an alternation of zones with low and high values of the Vp/Vs ratio, which are likely associated with the circulation of meteoric fluids in the uppermost crust. Moderately high Vp/Vs anomalies indicate zones of meteoric water penetration down to the ground. On the other hand, the very low values of Vp/Vs reaching 1.5 depict the areas where meteoric water reached the hot magma reservoir and transformed into steam. On the surface, these zones coincide with the distributions of fumaroles. The outflow of these steam currents from active vents of Korovin and Kliuchef led to episodic phreatic eruptions, sometimes synchronous.

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Section: Discussionmentioning

confidence: 61%

Section: Discussionmentioning

confidence: 82%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Magma Chambers and Meteoric Fluid Flows Beneath the Atka Volcanic Complex (Aleutian Islands) Inferred from Local Earthquake Tomography

2020

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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

Schaefer

Scott

Evans

et al. 2008

Geochem Geophys Geosyst

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[1] 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 Â 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 sulfur content. 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.

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References on Alaska and adjacent regions cited in The geology of Alaska

Weathers¹,

Plafker²

1998

Open-File Report

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Alaska Open-file Report 144 Assessment of Thermal Springs Sites Aleutian Arc, Atka Island to Becherof Lake -- Preliminary Results and Evaluation

Cited by 3 publications

References 0 publications

Magma Chambers and Meteoric Fluid Flows Beneath the Atka Volcanic Complex (Aleutian Islands) Inferred from Local Earthquake Tomography

Magma Chambers and Meteoric Fluid Flows Beneath the Atka Volcanic Complex (Aleutian Islands) Inferred from Local Earthquake Tomography

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

References on Alaska and adjacent regions cited in The geology of Alaska

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