We have analyzed trace elements in two types of hydrothermal precipitates using the Los Alamos Nuclear Microprobe. Chlorites and epidotes in basalt were analyzed from the Samail Ophiolite of Oman. Sulfide and sulfate minerals were analyzed from samples of active chimney walls from 21/degree/N. East Pacific Rise. These samples are ideal for our study because of the extensive background information available on processes and component characteristics. Initial results indicate significant differences in mobile trace elements between chlorites associated with and those distinctly separate from major stockwork flow zones, consistent with greater water-rock reaction within stockworks. Trace element concentrations across chimney walls also exhibit distinctive patterns which can be correlated with mineral/chemical zonation and possible also with variations in elemental source. 9 refs., 2 figs., 1 tab.

Erosion, hydrothermal activity, and magmatism at volcanoes can cause large and unex-pected mass wasting events. Large fluidized debris flows have occurred within the past 6000 yr at Mount Adams, Washington, and present a hazard to communities down-stream. In August 2017, we began a pilot experiment to investigate the potential of infra-sound arrays for detecting and tracking debris flows at Mount Adams. We deployed a telemetered four-element infrasound array (BEAR, 85 m aperture), similar to 11 km from a geo-logically unstable area where mass wasting has repeatedly originated. We present a pre-liminary analysis of BEAR data, representing a survey of the ambient infrasound and noise environment at this quiescent stratovolcano. Array processing reveals near continu-ous and persistent infrasound signals arriving from the direction of Mount Adams, which we hypothesize are fluvial sounds from the steep drainages on the southwest flank. We interpret observed fluctuations in the detectability of these signals as resulting from a combination of (1) wind-noise variations at the array, (2) changes in local infrasound propagation conditions associated with atmospheric boundary layer variability, and (3) changing water flow speeds and volumes in the channels due to freezing, thawing, and precipitation events. Suspected mass movement events during the study period are small (volumes < 10(5) m(3) and durations <2 min), with one of five visually confirmed events detected infrasonically at BEAR. We locate this small event, which satellite imagery suggests was a glacial avalanche, using three additional temporary arrays oper-ating for five days in August 2018. Events large enough to threaten downstream com-munities would likely produce stronger infrasonic signals detectable at BEAR. In complement to recent literature demonstrating the potential for infrasonic detection of volcano mass movements (Allstadt et al., 2018), this study highlights the practical and computational challenges involved in identifying signals of interest in the expected noisy background environment of volcanic topography and drainages.

Decades of exploration for venting sites along spreading ridge crests have produced global datasets that yield estimated mean site spacings of similar to 12-220 km. This conclusion demands that sites where hydrothermal fluid leaks from the seafloor are improbably rare along the 66 000 km global ridge system, despite the high bulk permeability of ridge crest axes. However, to date, exploration methods have neither reliably detected plumes from isolated low-temperature, particle-poor, diffuse sources, nor differentiated individual, closely spaced (clustered within a few kilometers) sites of any kind. Here we describe a much lower mean discharge spacing of 3-20 km, revealed by towing real-time oxidation-reduction-potential and optical sensors continuously along four fast- and intermediate-rate (>55 mm/yr) spreading ridge sections totaling 1470 km length. This closer spacing reflects both discovery of isolated sites discharging particle-poor plumes (25% of all sites) and improved discrimination (at a spatial resolution of similar to 1 km) among clustered discrete and diffuse sources. Consequently, the number of active vent sites on fast and intermediate-rate spreading ridges may be at least a factor of 3-6 higher than now presumed. This increase provides new quantitative constraints for models of seafloor processes such as dispersal of fauna among seafloor and crustal chemosynthetic habitats, biogeochemical impacts of diffuse venting, and spatial patterns of hydrothermal discharge. (C) 2016 Elsevier B.V. All rights reserved.

Numerous field, laboratory, and modeling studies have explored the flows of fluid, heat, and solutes during seafloor hydrothermal circulation, but it has been challenging to determine transport rates and flow directions within natural systems. Here we present results from the first cross-hole tracer experiment in the upper oceanic crust, using four subseafloor borehole observatories equipped with autonomous samplers to track the transport of a dissolved tracer (sulfur hexafluoride, SF6) injected into a ridge-flank hydrothermal system. During the first three years after tracer injection, SF6 was transported both north and south through the basaltic aquifer. The observed tracer transport rate of ∼2–3 m/day is orders of magnitude greater than bulk rates of flow inferred from thermal and chemical observations and calculated with coupled fluid-heat flow simulations. Taken together, these results suggest that the effective porosity of the upper volcanic crust through which much tracer was transported is <1%, with fluid flowing rapidly along a few well-connected channels. This is consistent with the heterogeneous (layered, faulted, and/or fractured) nature of the volcanic upper oceanic crust.

Processes that occur within and across the oceanic crust—in particular along mid‐ocean ridges and oceanic spreading centers—play a huge role in the dynamics of the Earth. The largest fluxes of heat and material between the Earth's mantle, crust, and seawater occur via magmatic, tectonic, and hydrothermal processes along oceanic spreading centers and their vast flanks. Roughly two thirds of the Earth's surface is accreted through magmatic and tectonic processes along mid‐ocean ridges, and subduction of this ocean crust in turn influences mantle compositions. Exchange of elements between ocean crust and seawater strongly influences seawater compositions and leaves a geologic record of fluid‐rock reactions in altered ocean crust. Some of these reactions contribute energy to microbial activity of a largely unexplored biosphere. The dynamics of ridge and ocean crustal processes therefore have enormous implications for thermal, chemical, and biological exchanges between the solid Earth and the hydrosphere.

Journal of MicroscopyVolume 236, Issue 1 p. 5-10 An improved method for nanogold in situ hybridization visualized with environmental scanning electron microscopy C.J. EHRHARDT, C.J. EHRHARDT Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106, U.S.A.Search for more papers by this authorR.M. HAYMON, R.M. HAYMON Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106, U.S.A.Search for more papers by this authorS.M. SIEVERT, S.M. SIEVERT Biology Department, Woods Hole Oceanographic Institute, Woods Hole, MA 02543, U.S.A.Search for more papers by this authorP.A. HOLDEN, P.A. HOLDEN Donald Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara CA 93106, U.S.A.Search for more papers by this author C.J. EHRHARDT, C.J. EHRHARDT Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106, U.S.A.Search for more papers by this authorR.M. HAYMON, R.M. HAYMON Department of Earth Science, University of California Santa Barbara, Santa Barbara, CA 93106, U.S.A.Search for more papers by this authorS.M. SIEVERT, S.M. SIEVERT Biology Department, Woods Hole Oceanographic Institute, Woods Hole, MA 02543, U.S.A.Search for more papers by this authorP.A. HOLDEN, P.A. HOLDEN Donald Bren School of Environmental Science and Management, University of California Santa Barbara, Santa Barbara CA 93106, U.S.A.Search for more papers by this author First published: 21 September 2009 https://doi.org/10.1111/j.1365-2818.2009.03207.xCitations: 9 C.J. Ehrhardt. Tel: +1 (805) 893-3718; fax: +1 (805) 893-2314; e-mail: [email protected] Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume236, Issue1October 2009Pages 5-10 RelatedInformation

The global mid-ocean ridge system generates two-thirds of the solid earth surface and produces more than half of the annual volcanic volume erupted on the earth. Active volcanic, hydrothermal, and structural processes mainly transpire within the first few million years of seafloor spreading, on the crest and young flanks of the mid-ocean ridge. In this active zone little sediment has yet accumulated, and only a thin crustal layer separates the oceans from the mantle. This young crust directly mediates extensive thermal, chemical, and biological exchanges between the hydrosphere and solid earth, releasing nearly half of the total oceanic hydrothermal heat flux. Yet the impact of these vast exchanges through young ocean crust remains poorly known, and include inorganic and organic carbon fluxes that may be important to earth's climate and biosphere. Although it was recognized more than 30 years ago that young ocean crust processes play a major role in the earth system, study of these processes has been impeded by insufficient access to the third dimension. Attempts to drill young ocean crust have been rare, and were stymied in the 1990's by stalled development of necessary drilling technology. Successful IODP drilling into older volcanic basement has greatly influenced mid-ocean ridge studies, but also has underscored the need for in situ measurement and samples from young ocean crust. New hard rock drilling tools and approaches have been developed by others as well as by IODP. Independent efforts to monitor hydrothermal and volcanic activity and the recent results of extensive seafloor mapping and seismic imaging offer logistical and scientific benefits. With a renewed commitment to engineering, integration of new tools, adequate support for scientists, and a general commitment to ocean crustal drilling, scientists are now poised to test many of the hypotheses in ocean ridge research through drilling of young ocean crust.

To explore effects of hot spots on mid‐ocean ridge hydrothermal systems, we conducted nested sonar, hydrothermal plume, and near‐bottom photographic surveys along the portion of the Galápagos Spreading Center (GSC) influenced by the Galápagos hot spot, from longitude 95°–89.5°W. We report the first active high‐temperature black smokers to be found on the GSC, at longitudes 94°4.5′W and 91°56.2′–54.3′W; describe two areas of recently inactive smokers, at longitudes 91°23.4′–23.7′W and 91°13.8′W; and document an older inactive site, at longitude 90°33.4′W. All imaged vents issue either from dike‐induced fissures along linear axial volcanic ridges and collapses or from a caldera. Magmatic control of hydrothermal systems also is revealed by spatial clustering of plumes within the topographically elevated middles of volcanic ridge segments with inferred centralized melt supply. In searched areas, smokers are more typical than diffuse flow vents, but total GSC plume incidence is half of that expected from the spreading rate. Why? Dike‐fed fissures provide permeable pathways for efficient hydrothermal extraction of magmatic heat, but cones without calderas do not. Among many point‐source cones surveyed, only the two with calderas had detectable plumes. Possibly, dominance of point‐source over linear‐source melt delivery on the GSC decreases plume incidence. Also, similar maturities of observed vents and their host lava flows indicate that hydrothermally active volcanic segments along the western GSC are contemporaneously in a waning phase of volcanic‐hydrothermal activity. Perhaps ridge/hot spot interaction produces melt pulses that drive near‐synchronous volcanic‐hydrothermal activity on the volcanic segments spanning the hot spot. During active periods, hydrothermally active dike‐fed fissures and calderas may be more abundant than we currently observe.

The Galápagos Spreading Center (GSC) at 89°–95°W exhibits large gradients in magma supply at a relatively constant intermediate spreading rate, making this area an ideal natural laboratory to study the effects of magma supply on volcanism at seafloor spreading ridges. Prior work shows that the GSC develops from axial valley to shallow axial rise and a shallow magma sill, much like a typical fast spreading ridge, as the contribution of the hot spot increases. The volcanic morphology varies with magma supply in a predictable manner that we divide into three terrains based on the characteristic style of volcanic emplacement and edifice construction within each terrain. The volcanic cone terrain comprises most of the GSC and is characterized by prominent volcanic cones within a >1 km wide and >100 m deep axial graben. Approaching the area of maximum mantle plume influence at 91°W, the GSC axis lies along an elevated axial rise split by a <1 km wide and <100 m deep axial graben, and the style of volcanism shifts to axial volcanic ridge terrain characterized by axis‐elongate, low‐relief ridges of pillow lava. The lava channel terrain comprises only one segment on either side of the maximum magma supply at 91°W, where sheet lava flows and lava channels are relatively widespread. A general lengthening of seafloor fissures with increasing magma supply suggests a greater tendency toward linear source eruptions, in agreement with the volcanic observations. These results suggest that magma supply rather than magma chamber depth or rate of tectonic extension is the primary influence on lava morphology, hence eruptive processes, at seafloor spreading ridges in general. In both the axial volcanic ridge and lava channel terrains, a single prominent volcanic cone exists within each volcanic segment, suggesting a segment‐centered magma focusing.

Karen L. Von Damm, a professor and world‐renowned researcher in marine geochemistry at the University of New Hampshire, passed away at her home in Durham on 15 August 2008, after having been diagnosed with liver cancer in April 2008. She was 53 years old.

The spatial density of hydrothermal activity along most mid‐ocean ridges is a robust linear function of spreading rate (or magmatic budget), but extreme crustal properties may alter this relationship. In 2005–2006 we tested the effect of thickened crust on hydrothermal activity using high‐resolution mapping of plumes overlying the hot spot–affected Galápagos Spreading Center from 95° to 89°42′W (∼560 km of ridge crest). Plume mapping discovered only two active, high‐temperature vent fields, subsequently confirmed by camera tows, though strong plume evidence indicated minor venting from at least six other locations. Total plume incidence (ph), the fraction of ridge crest overlain by significant plumes, was 0.11 ± 0.014, about half that expected for a non–hot spot mid‐ocean ridge with a similar magmatic budget. Plume distributions on the Galápagos Spreading Center were uncorrelated with abrupt variations in the depth of the along‐axis melt lens, so these variations are apparently not controlled by hydrothermal cooling differences. We also found no statistical difference (for a significance level of 0.05) in plume incidence between where the seismically imaged melt lens is shallow (2 ± 0.56 km, ph = 0.108 ± 0.045) and where it is deep (3.4 ± 0.7 km, ph = 0.121 ± 0.015). The Galápagos Spreading Center thus joins mid‐ocean ridges near the Iceland (Reykjanes Ridge), St. Paul‐Amsterdam (South East Indian Ridge), and Ascension (Mid‐Atlantic Ridge) hot spots as locations of anomalously scarce high‐temperature venting. This scarcity implies that convective cooling along hot spot–affected ridge sections occurs primarily by undetected diffuse flow or is permanently or episodically reduced compared to normal mid‐ocean ridges.

Little is known about the fluids or the microbial communities present within potentially vast hydrothermal reservoirs contained in still-hot volcanic ocean crust beneath the flanks of the mid-ocean ridge. During Alvin dives in 2002, organic material attached to basalt was collected at low, near-ambient temperatures from an abyssal hill fault scarp in 0.5 Ma lithosphere on the western ridge flank of the East Pacific Rise. Mineral analysis by X-ray diffractometry and scanning electron microscopy revealed high-temperature (> 110 degrees C) phases chalcopyrite (Cu(5)FeS(4)) and 1C pyrrhotite (Fe(1-x)S) within the fault scarp materials. A molecular survey of archaeal genes encoding 16S rRNA identified a diverse hyperthermophilic community, including groups within Crenarchaeota, Euryarchaeota, and Korarchaeota. We propose that the sulfide, metals and archaeal communities originated within a basalt-hosted subseafloor hydrothermal habitat beneath the East Pacific Rise ridge flank and were transported to the seafloor during a recent episode of hydrothermal venting from the abyssal hill fault. Additionally, inferred metabolisms from the fault scarp community suggest that an ecologically unique high-temperature archaeal biosphere may thrive beneath the young East Pacific Rise ridge flank and that abyssal hill fault scarps may present new opportunities for sampling for this largely unexplored microbial habitat.