Newberry Volcano Research Articles

De-risking superhot EGS development through 3D play fairway analysis: Methodology development and application at Newberry Volcano, Oregon, USA

The DErisking Exploration for multiple geothermal Plays in magmatic ENvironments (DEEPEN) project aims to de-risk exploration of geothermal plays in magmatic systems, with a focus on superhot and supercritical geothermal systems. This article presents advancements in geoscientific assessment of superhot enhanced geothermal system (EGS) resources as part of the DEEPEN project, particularly in exploration and identification of these systems. While there exists a general consensus on key components of conventional hydrothermal systems, there has not been a prior consensus on such components for EGS, let alone superhot EGS. The DEEPEN project identified these key components for superhot EGS plays, and used them to modify the traditional geothermal play fairway analysis (PFA) approach to identify favorable areas in superhot EGS plays in 3D. This was done through modeling both favorability and uncertainty separately for each key component of a superhot EGS play, incorporating diverse 3D geoscientific datasets, including geologic features, models produced from direct observations, single inversions, and joint inversions. The PFA is applied to Newberry Volcano as a form of validation. The results appear to validate the methodology, aligning with expectations derived from conceptual modeling, and highlighting the area targeted for EGS stimulation well NWG 55-29 as favorable, and suggesting potential additional areas worthy of exploration at Newberry.

Contrasting magmatic evolutions of the Three Sister Volcanoes reflect increased heat flow, crustal melting and silicic magmatism in the Central Oregon Cascade Arc

The Three Sisters stretch, one of the most magmatically active segments of the Oregon Cascade Arc, includes the Three Sisters volcanoes proper (North, Middle and South) as well as the shields and cinder cones of the Mount Bachelor Chain and McKenzie Pass. The Three Sisters record a magmatic transition from fundamentally basaltic andesitic activity in older North Sister products to more diverse activity at Middle Sister, and unusually silicic activity in a Cascade volcano, including rhyolite lava, at South Sister.North Sister magmas reflect magmatic evolution of basaltic andesite through crystal fractionation, mostly of olivine, and incorporation of crustal melts. Middle Sister, although mostly composed of basaltic andesite and andesite, produced dacitic magma through assimilation fractional crystallization processes involving incorporation of silicic melts. South Sister developed a subjacent magma chamber under the southern half of the volcano, where andesitic magmas evolved, dominantly through fractional crystallization, to dacite and rhyolite. A prominent compositional gap at South Sister between dacite and rhyolite and depletion of middle and heavy rare earth elements in rhyolite suggest that amphibole was prominently involved in fractionation processes involving separation of silicic magma from a gabbroic or amphibolitic crystal mush. Silicic magma eventually formed a stagnant cap in the system, where it evolved through small scale fractional crystallization. Rhyolite magma was finally heated to elevated temperatures prior to eruption, presumably through influx of less evolved magma into the base of the stagnant silicic cap and was erupted in late rhyolite lava of Rock Mesa and the Devil's Hill Chain.South Sister lies along strike of the Northwest Rift of Newberry Volcano, which forms the northwestern terminus of the High Lava Plains trend of south-central Oregon. The increased magmatic activity of the Three Sisters stretch and unusual abundance of silicic products, including rhyolite, of South Sister may reflect the arrival and intersection of the High Plains magmatic anomaly with the Cascade Arc.

Geochemistry and fluxes of gases from hydrothermal features at Newberry Volcano, Oregon, USA

We present the chemical and isotopic compositions of gases and fluxes of CO2 from the hydrothermal features of Newberry Volcano, a large composite volcano located in Oregon's Cascade Range with a summit caldera that hosts two lakes, Paulina and East Lakes. Gas samples were collected from 1982 to 2021 from Paulina Hot Springs (PHS) on the shore of Paulina Lake, East Lake Hot Springs (ELHS) on the shore of East Lake, and Obsidian Flow Gas Seep (OFGS), an area of diffuse gas emissions. Surveys of CO2 flux were conducted in 2020 at OFGS (1400 m2) and East Lake (4.1 km2). Gases from all three sites were CO2-rich (≥79 mol% in dry gas) but showed considerable compositional variability over time due to interaction with ground and surface water. An increase in H2S concentrations and decline in CO2/H2S ratios in ELHS gases coincided with a drop in East Lake water level from 1999 to 2021. ELHS and OFGS gases were high in CH4 relative to PHS and the δ13C of CH4 values for ELHS gases (−72.2 and − 63.6 ‰) reflected a predominantly biogenic origin. The dominant source of N2 and Ar in PHS, ELHS, and OFGS samples was likely groundwater. Helium isotopic ratios (6.47 to 8.02 Rc/Ra) support a persistent source of magmatic He beneath Newberry caldera and consistently high values measured at OFGS and PHS relative to ELHS suggest distinct fluid flow paths from depth to the surface features. The δ13C of CO2 and CO2/3He values (−8.9 to −5.35 ‰ and 1.3 × 109 to 4.6 × 1010, respectively) measured in gases reflect contributions of CO2 from both mantle and crustal sources. Measured CO2 fluxes at OFGS and East Lake ranged from 1 to 8808 and < 1 to 364 g m−2 d−1, respectively. A CO2 emission rate of 0.5 t d−1 was calculated for OFGS. The CO2 emission rate estimated for East Lake was 30 t d−1 and when compared to prior estimates, reflects steady-state lake degassing. An enhanced geochemical monitoring plan, including annual sampling of gases at ELHS, OFGS, and PHS for geochemical analysis, installation of a continuous lake-level monitoring station at East Lake, and annual CO2 flux surveys at OFGS, would provide valuable background data and insights into any precursor volcanic activity. Integrating geochemical data with data from the real-time seismic and GPS network at Newberry Volcano could better resolve and interpret potential changes in its magma-hydrothermal system.

The pivotal role of Vulcanian activity in ending the explosive phase of rhyolitic eruptions: the case of the Big Obsidian Flow eruption (Newberry Volcano, USA)

The pivotal role of Vulcanian activity in ending the explosive phase of rhyolitic eruptions: the case of the Big Obsidian Flow eruption (Newberry Volcano, USA)

Filling critical gaps in the space-time record of High Lava Plains and co-Columbia River Basalt Group rhyolite volcanism

Miocene rhyolitic volcanism of eastern Oregon, USA, can be divided into two main episodes. Mantle plume upwelling is thought to have generated Columbia River Basalt Group (CRBG) lavas and coeval &amp;gt;16.5−15 Ma silicic volcanism trending north−south from northeast Oregon to northern Nevada. Rhyolite volcanism of the 12−0 Ma High Lava Plains province has been ascribed to either buoyancy-driven westward plume spreading or to slab rollback and mantle convection spanning from southeast Oregon to Newberry Volcano to the west. The apparent ca. 15−12 Ma eruptive hiatus suggests that rhyolites of these provinces were a product of separate processes, yet this gap was based on incomplete data. The lack of data on ∼33 of the total ∼50 rhyolitic eruptive centers in the area where the two provinces overlap (117−119°W, 43−44°N) yields only tenuous relationships between these two provinces. We acquired 40Ar/39Ar ages for 29 previously unanalyzed rhyolite centers that confirm the existence of a rhyolitic eruptive episode concurrent with CRBG flood basalt volcanism. Rhyolite eruptions gradually initiated at ca. 17.5 Ma, and our new ages indicate that peak intensity of the first eruptive episode occurred between 16.3 Ma and 14.4 Ma. We refine the ca. 15−12 Ma rhyolitic eruptive hiatus to 14.4−12.1 Ma, where strong recommencement of rhyolite eruptions began with Beatys Butte at 12.05 Ma. We find two prominent fluxes in rhyolitic eruptive activity after 12.1 Ma as opposed to one continuous, age-progressive trend, at 12.1−9.6 Ma and 7.7−5.1 Ma, which are separated by an ∼2 m.y. period of decreased rhyolite volcanism. Rhyolite eruptions were scarce after 5.1 Ma, at which point most eruptions were associated with Newberry Volcano. Periodicity of rhyolite volcanism along the High Lava Plains demands more punctuated basalt inputs than what continuous partial melting from west-spreading plume material should generate. Our new data suggest that regional rhyolite eruptions are a series of episodic events related to the arrival and storage of mafic mantle magmas. Paucity in rhyolite eruptions from 14.4 Ma to 12.1 Ma is related to decreased flux of CRBG flood basalt magmas at ca. 15 Ma. Strong recommencement of rhyolite volcanism at 12.1 Ma is related to continued Northwest Basin and Range extension and a peak rotation rate of Siletzia affecting regional lithosphere weakened by CRBG volcanism. Waning rhyolitic eruptive activity from ca. 9.6 Ma to 7.7 Ma reflects a regional transition in the primary mode of accommodation of extension from Northwest Basin and Range normal faulting to extension and shearing of the Brothers Fault Zone. Rhyolite volcanism between 7.7 Ma and 5.1 Ma was driven by continued regional extension in an area less affected by CRBG magmatism. Post-5.1 Ma rhyolite eruptions occurred within crust not influenced by CRBG magmatism but impacted by both regional extension and the Cascadia subduction zone.

Constraining Magma Reservoir Conditions by Integrating Thermodynamic Petrological Models and Bulk Resistivity From Magnetotellurics

AbstractMagnetotelluric (MT) data image the bulk resistivity of the subsurface which can be used to infer magma reservoir conditions beneath volcanoes. The bulk resistivity of magma depends primarily on the melt volume fraction, temperature, and water content. These variables are coupled thermodynamically, yet mixing relations for bulk resistivity implicitly treat them as independent. Here, we use a parameterization of the rhyolite‐MELTS thermodynamic model to constrain relationships between melt fraction, temperature, dissolved water content and bulk resistivity for rhyolitic magmas. This method results in MT interpretations which are (a) thermodynamically consistent at near‐equilibrium conditions, (b) independent of temperature and water content estimates derived from erupted products, and (c) able to consider saturated melts containing a volatile (i.e., aqueous fluid) phase. The utility of the method is demonstrated with three case studies of silicic systems: Mono Basin, Newberry volcano and the Laguna del Maule Volcanic Field (LdMVF). The moderately conductive feature at Mono Basin can be explained by under‐saturated partial melt (6–15 vol%) at &lt;775°C, indicating relatively stable magma storage conditions since the last eruption. However, a relatively resistive feature at Newberry Volcano requires lower temperatures (&lt;750°C) than previous estimates, suggesting that the system has cooled since the last eruption. A conductive feature at the LdMVF cannot be explained by saturated or under‐saturated rhyolitic melt and requires additional conductive phases. These results demonstrate the potential of this new method to reduce uncertainty in MT interpretations and highlight the need for additional coupling strategies between petrology, geophysics, and thermo‐mechanical models to better understand magmatic systems.

Extensive hybridization of mafic and silicic magmas at the confluence of the Cascade Arc and High Lava Plains: The Newberry Volcano of Central Oregon

Newberry volcano lies at the intersection of the north-south trending Cascade Arc with the margin of the High Lava Plains trend. Newberry is unusual as a Cascade volcano in that it is dominantly basaltic and geochemically bimodal between basalt and silicic rocks. The youngest calc-alkaline mafic to intermediate lavas of Newberry Volcano have major and trace element characteristics consistent with up to 35–40 wt% mixing and hybridization of an evolved tholeiitic basalt with silicic magmas similar to that present as domes and flows within the caldera of the volcano. This unusual extensive hybridization is the combined result of voluminous influx of basaltic magma into the crust, fractionation within subvolcanic chambers, anatexsis of crustal rocks to produce silicic magmas, superheating of these silicic magmas, and complex interaction of mafic and silicic magma within the substructure of the volcano and especially within a dike swarm underlying the northwest rift of the volcano.The most primitive basaltic rocks of the volcano include both tholeiitic and calc-alkaline varieties derived from melting of variously subduction-influenced lithospheric mantle at depth. The evolved tholeiitic end member of mixing within the Northwest Rift was produced by fractionation of a primitive tholeiitic parent. This evolved tholeiite mixed substantially with at least two silicic magmas to generate the calc-alkaline intermediate rocks of the Northwest Rift of the volcano.

Numerical Analysis of Enhanced Conductive Deep Borehole Heat Exchangers

Geothermal energy is a reliable and mature energy source, but it represents less than 1% of the total renewable energy mix. While the enhanced geothermal system (EGS) concept faces technical validation challenges and suffers from public acceptance issues, the development of unconventional deep-well designs can help to improve their efficiency and reliability. Modelling single-EGS-well designs is key to assessing their long-term thermal performances, particularly in unconventional geological settings. Numerical results obtained with the T2WELL/EOS1 code have been validated with available experimental data from a deep borehole heat exchanger (DBHE), where a temperature of 358 ∘C has been measured at a depth of 1962 m. Based on a calibrated model, the thermal performances of two enhanced thermal conductive DBHEs with graphite were compared for high geothermal gradients. The analysis highlights the potential recovery of a variable fraction of vapour. Graphite used along the well appears to be the most suitable solution to enhance the thermal output by 5 to 8% when compared to conventional wells. The theoretical implementation of such well in the Newberry volcano field was investigated with a single and doublet DBHE. The findings provide a robust methodology to assess alternative engineering solutions to current geothermal practices.

Volcanic carbon cycling in East Lake, Newberry Volcano, Oregon, USA

Abstract The carbon cycle in East Lake (Newberry Volcano, Oregon, USA) is fueled by volcanic CO2 inputs with traces of Hg and H2S. The CO2 dissolves in deep lake waters and is removed in shallow waters through largely diffusive surface degassing and photosynthesis. Escaping gas and photosynthate have low δ13C values, leading to δ13C(DIC) (DIC—dissolved inorganic carbon) as high as +5.7‰ in surface waters, well above the common global lake range. A steep δ13C depth gradient is further established by respiration and absorption of light volcanic CO2 in bottom waters. The seasonal CO2 degassing starts at &amp;gt;100 t CO2/day after ice melting in the spring and declines to ∼40 t/day in late summer, degassing ∼11,700 t CO2/yr. Thus, volcano monitoring through gas fluxes from crater lakes should consider lacustrine processes that modulate the volcanic gas output over time. The flux contribution of a bubbling CO2 “hotspot” increased from 20% to &amp;gt;90% of the lake-wide CO2 flux from 2015 to 2019 CE, followed by a “toxic gas alert” in July 2020. East Lake is an active volcanic lake with a “geogenic” ecosystem driven primarily by hydrothermal inputs.

Modelling an unconventional closed-loop deep borehole heat exchanger (DBHE): sensitivity analysis on the Newberry volcanic setting

Alternative (unconventional) deep geothermal designs are needed to provide a secure and efficient geothermal energy supply. An in-depth sensitivity analysis was investigated considering a deep borehole closed-loop heat exchanger (DBHE) to overcome the current limitations of deep EGS. A T2Well/EOS1 model previously calibrated on an experimental DBHE in Hawaii was adapted to the current NWG 55-29 well at the Newberry volcano site in Central Oregon. A sensitivity analysis was carried out, including parameters such as the working fluid mass flow rate, the casing and cement thermal properties, and the wellbore radii dimensions. The results conclude the highest energy flow rate to be 1.5 MW, after an annulus radii increase and an imposed mass flow rate of 5 kg/s. At 3 kg/s, the DBHE yielded an energy flow rate a factor of 3.5 lower than the NWG 55-29 conventional design. Despite this loss, the sensitivity analysis allows an assessment of the key thermodynamics within the wellbore and provides a valuable insight into how heat is lost/gained throughout the system. This analysis was performed under the assumption of subcritical conditions, and could aid the development of unconventional designs within future EGS work like the Newberry Deep Drilling Project (NDDP). Requirements for further software development are briefly discussed, which would facilitate the modelling of unconventional geothermal wells in supercritical systems to support EGS projects that could extend to deeper depths.

Composition of Magma and Characteristics of the Hydrothermal System of Newberry Volcano, Oregon, From Magnetotellurics

AbstractWe use 3‐D magnetotellurics to improve our understanding of the structure and magma composition of Newberry Volcano in Oregon, USA. Newberry is a broad shield volcano with a summit caldera and strongly bimodal magmatism. Newberry has long been the subject of geothermal exploration research, but that work has focused on the volcano's west flank, leaving the caldera largely unstudied with geophysical methods until recently. Our modeling shows a relatively resistive magma reservoir of approximately 50 Ωm. Our work builds upon recent seismic models and petrological analysis to interpret Newberry's magma reservoir as a dry rhyolite with 8–11% partial melt, which matches the seismically determined melt fraction. Finding the conditions within the magma reservoir that allow the resistivity and seismic analysis to come to the same melt fraction helps us narrow down the magma temperature and composition. From this we infer a dry rhyolitic magma at 850 °C. We also image a prominent vertical conductive anomaly along the south rim below the vent that produced the most recent eruption. The anomaly extends from magma reservoir depths of 3 km to 1 km below the surface where it disperses into the caldera fill. We interpret this as the main conduit for magmatic fluids to reach Newberry's hydrothermal system. Other features that our model shows include higher conductivity along the caldera rim and a resistive older pluton on the west flank.

Microseismic Focal Mechanisms and Implications for Changes in Stress during the 2014 Newberry EGS Stimulation

Abstract We adapt the relative polarity method from Shelly et al. (2016) to compute focal mechanisms for microearthquakes associated with the 2014 hydroshearing stimulation at the Newberry volcano geothermal site. We focus the analysis on events relocated by Aguiar and Myers (2018), who report that six event clusters predominantly comprise the 2014 sequence. Data quality allows focal mechanism analysis for four of the six event clusters. We use Hardebeck and Shearer (2002, 2003; hereafter HASH) to compute focal mechanisms based on first‐motion polarities and S/P amplitude ratios. We manually determine P‐ and S‐wave polarities for a well‐recorded reference event in each cluster, then use waveform cross correlation to determine whether recordings of other events in the cluster are the same or reversed polarity at each network station. Most waveform polarities are consistent with the affiliated reference event, indicating similar focal mechanisms within each cluster. The deeper clusters are east–west‐striking normal faults, whereas the shallower clusters, close to the top of the open‐hole section of the borehole, are strike slip with east–west motion. Regional studies and prestimulation borehole breakouts find the maximum stress direction is vertical and maximum horizontal stress is approximately north–south. Fault geometry and focal mechanisms of microseismicity during the stimulation suggest that increased pressure from fluid injection predominantly caused changes in horizontal stress, consistent with predictions from numerical studies of stress change caused by fluid injection. At shallow depths, where previous studies suggest the difference between vertical and horizontal stress is lowest, injection appears to have rotated the direction of maximum stress from vertical to horizontal, resulting in strike‐slip motion. At greater depth, vertical stress continued to be the dominant direction during the stimulation, but fault orientation indicates either reactivation of pre‐existing fractures or rotation of the direction of maximum horizontal stress from approximately north–south to east–west.

The Newberry Deep Drilling Project (NDDP) workshop

Abstract. The important scientific questions that will form the basis of a full proposal to drill a deep well to the ductile–brittle transition zone (T&gt;400 ∘C) at Newberry Volcano, central Oregon state, USA, were discussed during an International Continental Drilling Program (ICDP) sponsored workshop held at the Oregon State University-Cascades campus in Bend, Oregon, from 10 to 13 September 2017. Newberry Volcano is one of the largest geothermal heat reservoirs in the USA and has been extensively studied for the last 40 years. The Newberry Deep Drilling Project (NDDP) will be located at an idle geothermal exploration well, NWG 46-16, drilled in 2008, 3500 m deep and 340–374 ∘C at bottom, which will be deepened another 1000 to 1300 m to reach 500 ∘C. The workshop concluded by setting ambitious goals for the NDDP: (1) test the enhanced geothermal system (EGS) above the critical point of water, (2) collect samples of rocks within the brittle–ductile transition, (3) investigate volcanic hazards, (4) study magmatic geomechanics, (5) calibrate geophysical imaging techniques, and (6) test technology for drilling, well completion, and geophysical monitoring in a very high-temperature environment. Based on these recommendations, a full drilling proposal was submitted in January 2018 to the ICDP for deepening an existing well. The next steps will be to continue building a team with project, technology, and investment partners to make the NDDP a reality.

Microseismic Event Relocation Based on PageRank Linkage at the Newberry Volcano Geothermal Site

Microseismic Event Relocation Based on PageRank Linkage at the Newberry Volcano Geothermal Site

Bubble deformation in magma under transient flow conditions

We investigate the transient behavior of bubble deformation in magma. Previous studies have used the relationships between capillary number and equilibrium shape for a single bubble under either steady simple shear or steady pure shear to estimate strain rates in pyroclasts and to calculate bubble shapes in a conduit flow. We developed a deformation model for a bubble by adjusting the empirical functions used in an existing model for a droplet to fit experimental data for bubble deformation. The modified model was used to calculate transient large deformations of a single bubble in arbitrary shear flows. In this paper, we demonstrate the significance of the modified model through two different applications. Firstly, using this model, we are able to simulate the entire history of the evolution of bubble shapes in a time dependent flow using the computational code, Conflow. In this simulation, we further include the effect of gas expansion on the bubble shape. From this simulation, we show that bubble deformation in conduit flow is controlled by the history of both capillary number and strain. Secondly, by using this model to analyze bubble shapes observed in natural magma samples, we are able to better estimate the strain rates and deformation durations. We apply this model to certain transient features in the relationship between bubble shape and radius in the published data of obsidian clasts from Newberry Volcano and estimate a deformation duration of 2.7–4.0 min.

Origin of Primitive Tholeiitic and Calc‐Alkaline Basalts at Newberry Volcano, Oregon

AbstractMajor and trace element and radiogenic isotopic characteristics of primitive mafic Pleistocene and Holocene lavas from Newberry Volcano, Oregon, define two groups. The first consists of dry tholeiitic high‐alumina olivine basalts that are slightly enriched in highly incompatible elements. The second group consists of calc‐alkaline basalts that contained 2–4 wt % H2O prior to eruption and shows strong enrichment in the light rare earth elements, Ba, and Sr, and deficits in Nb, Ta, Hf, and Zr. The tholeiitic basalts reflect 6–11% anhydrous adiabatic decompression melting of spinel peridotite. The calc‐alkaline basalts derived from compositionally distinct sources with strong LIL enrichment and relative depletion in HFSE, but with Sr, Nd, Hf, and Pb isotopic composition only slightly distinct from the sources of the tholeiitic magmas. Radiogenic Os correlates with LREE enrichment in the calc‐alkaline magmas, which indicates that their source materials include a contribution from a mafic component that was melted in the garnet stability field. The calc‐alkaline magmas were derived by melting of peridotite metasomatized by a fluid/melt that originated by melting of a mixture of the sediment plus MORB basalt/mantle in the underlying subducting oceanic plate. While the trace element characteristics of the calc‐alkaline magmas were determined by the subduction component, their isotopic characteristics were modified during transit through the mantle by interaction with the highly magmatically processed mantle wedge beneath Newberry Volcano that, without the slab component, serves as the source of the tholeiitic magmas.

Autocorrelation of the Seismic Wavefield at Newberry Volcano: Reflections From the Magmatic and Geothermal Systems

AbstractWe show that seismic autocorrelations provide new depth constraints on upper crustal magmatic systems. Autocorrelations of both ambient noise recorded on seismometers and geophones and teleseismic earthquake coda recorded on seismometers elucidate the structure of Newberry Volcano. These autocorrelations result in the two‐way, body wave Green's function beneath a station. Within the caldera, a reproducible, coherent P wave reflection is inferred to come from the top of a magma body at ~2.5 km depth and maps with the lateral extent of an anomalously low‐velocity body imaged tomographically. On the west flank of the volcano, a reflection that deepens with distance from the caldera is inferred to result from a temperature‐dependent change in metamorphic facies and may map the thermal structure of the edifice. Our results show that the autocorrelation of diffuse seismic energy reconstructs reflections from seismically sharp boundaries associated with the upper crustal magmatic structure.

Volcano geodesy in the Cascade arc, USA

Experience during historical time throughout the Cascade arc and the lack of deep-seated deformation prior to the two most recent eruptions of Mount St. Helens might lead one to infer that Cascade volcanoes are generally quiescent and, specifically, show no signs of geodetic change until they are about to erupt. Several decades of geodetic data, however, tell a different story. Ground- and space-based deformation studies have identified surface displacements at five of the 13 major Cascade arc volcanoes that lie in the USA (Mount Baker, Mount St. Helens, South Sister, Medicine Lake, and Lassen volcanic center). No deformation has been detected at five volcanoes (Mount Rainier, Mount Hood, Newberry Volcano, Crater Lake, and Mount Shasta), and there are not sufficient data at the remaining three (Glacier Peak, Mount Adams, and Mount Jefferson) for a rigorous assessment. In addition, gravity change has been measured at two of the three locations where surveys have been repeated (Mount St. Helens and Mount Baker show changes, while South Sister does not). Broad deformation patterns associated with heavily forested and ice-clad Cascade volcanoes are generally characterized by low displacement rates, in the range of millimeters to a few centimeters per year, and are overprinted by larger tectonic motions of several centimeters per year. Continuous GPS is therefore the best means of tracking temporal changes in deformation of Cascade volcanoes and also for characterizing tectonic signals so that they may be distinguished from volcanic sources. Better spatial resolution of volcano deformation can be obtained through the use of campaign GPS, semipermanent GPS, and interferometric synthetic aperture radar observations, which leverage the accumulation of displacements over time to improve signal to noise. Deformation source mechanisms in the Cascades are diverse and include magma accumulation and withdrawal, post-emplacement cooling of recent volcanic deposits, magmatic-tectonic interactions, and loss of volatiles plus densification of magma. The Cascade Range thus offers an outstanding opportunity for investigating a wide range of volcanic processes. Indeed, there may be areas of geodetic change that have yet to be discovered, and there is good potential for addressing a number of important questions about how arc volcanoes work before, during, and after eruptions by continuing geodetic research in the Cascade Range.

A tale of two lakes: the Newberry Volcano twin crater lakes, Oregon, USA

Abstract Newberry Volcano in Oregon, USA, has two small crater lakes inside its caldera: East Lake and Paulina Lake. The 50–80 m deep lakes differ in morphology, water chemistry and sediment composition, although separated only by a narrow volcanic ridge. East Lake is a terminal lake with gaseous geothermal inputs, whereas Paulina Lake has an outlet (Paulina Creek) and subaqueous, high-alkalinity hot springs. The sediment in both lakes is organic-rich and mainly consists of diatom frustules (SiO 2 ) with some volcanic ash, accumulating at sedimentation rates of 1.5–2 mm a −1 ( 210 Pb dated). In Paulina Lake the sediment has up to 14% Fe 2 O 3 of hydrothermal origin and 250 ppm As. Sediment in East Lake is Fe-poor but has up to 4 ppm Hg, and fish are also Hg-rich. Both lakes host productive ecosystems, with primary producers using geothermal CO 2 , P and Si, and nitrogen fixed by cyanobacteria ( Nostoc sp.). Water budgets and water residence times were calculated from stable isotope budgets. East Lake has a steep vertical δ 13 C (dissolved inorganic carbon, DIC) gradient, with surface δ 13 C values of up to 5.5‰, largely due to diffusional CO 2 losses and photosynthetic carbon withdrawal. Paulina Lake is better mixed, has a lower organic productivity and limited surface CO 2 evasion; its δ 13 C (DIC) gradient is small. We theorize that the lakes are fed by different geothermal components as a result of phase separation below East Lake. The gas component (CO 2 , H 2 S, Hg) enters East Lake, as indicated by the rising bubble trains in the lake. A residual fluid, depleted in Hg but rich in Si, Fe, carbonate, P and As, enters Paulina Lake. The presence of highly toxic components and the gas-charging of East Lake present natural hazards, which may change when new volcanic activity is initiated, and thus should be monitored.

A loess record of pre-Late Wisconsin glacial outburst flooding, Pleistocene paleoenvironment, and Irvingtonian fauna from the Rulo site, southeastern Washington, USA

Worldwide, loess-paleosol sequences are archives of terrestrial Quaternary paleoenvironment data. The Rulo site is a newly described site in the Palouse loess of southeastern Washington State, USA. The site reveals a 19m thick deposit of loess and flood sediment, preserving a total of 30m of reconstructed stratigraphic section. Five unconformity-bound sequences of sediment are exposed at the site, the lowest two of which have yielded fossil remains, including the first reported occurrence of flat-headed peccary (Platygonus compressus) in northwestern North America. The unconformities, two diamicts bearing extrabasinal clasts, and a number of clastic dikes provide evidence for pre-Wisconsin glacial outburst floods in southeastern Washington. More than a dozen paleosols are preserved at the site. These soils are relatively unweathered and therefore primarily record periods of slow sedimentation accumulation in the Palouse, rather than changes in weathering rates. A paleosol near the base of the sequence is unusually weathered for Palouse paleosols, and records a period of increased weathering during the Middle Pleistocene. All units above the sand are normal paleomagnetic polarity; additional age control is provided by a tephra in the upper third of the sequence that matches a ca. 220ka tephra from Newberry Volcano, and by stratigraphic correlation of later units to other sites in the Palouse. The Rulo site adds to the record of Irvingtonian fauna in North America, and supports accumulating evidence for pre-Late Wisconsin glacial outburst floods in the Pacific Northwest.