Valley Caldera Research Articles

Rotaphone-D, A New Model of Six-Degree-of-Freedom Seismic Sensor: Description and Performance

Abstract A new model of the Rotaphone-D short-period seismic sensor with six degrees of freedom is introduced. The basis of the instrument is horizontal and vertical geophones in a special paired arrangement. The instrument is designed for simultaneous and collocated measurements of rotational and translational components of ground motion. The basic principle of measurement is briefly described. Careful calibration is necessary for this type of measurement, which has two parts: a preliminary calibration based on laboratory measurements of the characteristics of the individual geophones, and a subsequent in situ calibration, which takes into account the actual physical conditions during field measurements and is performed during the processing of the measured data. The effect of the calibration is demonstrated by specific laboratory tests. The laboratory tests have confirmed the correct functioning of the instrument. The frequency range of Rotaphone-D is from 2 to 80 Hz and is therefore optimal for monitoring local seismicity. The instrument was subsequently used in field measurements during two several-month measurement campaigns in California, United States. Examples of six-component records from two sites—The Geysers and Long Valley Caldera—are presented and briefly interpreted from a seismological perspective. Basic instrument parameters are given. The instrument is lightweight, portable, easy to install, and offers several interesting applications, which are briefly discussed. Six-component measurements (translational and rotational) have become a powerful tool, especially in volcanic seismology and in monitoring induced seismicity.

Gradient-based joint inversion of point-source moment tensor and station-specific time-shifts

SUMMARY The misalignment of the observation and predicted waveforms in regional moment tensor inversion is mainly due to seismic models’ incomplete representation of the Earth's heterogeneities. Current moment tensor inversion techniques, allowing station-specific time-shifts to account for the model error, are computationally expensive. Here, we propose a gradient-based method to jointly invert moment-tensor parameters, centroid depth and unknown station-specific time-shifts utilizing the modern functionalities in deep learning frameworks. A $L_2^2$ misfit function between predicted synthetic and time-shifted observed seismograms is defined in the spectral domain, which is differentiable to all unknowns. The inverse problem is solved by minimizing the misfit function with a gradient descent algorithm. The method's feasibility, robustness and scalability are demonstrated using synthetic experiments and real earthquake data in the Long Valley Caldera, California. This work presents an example of fresh opportunities to apply advanced computational infrastructures developed in deep learning to geophysical problems.

Geologically-derived nitrogen and phosphorus as a source of riverine nutrients

The role of geological-derived nitrogen (N) and phosphorus (P) as sources of riverine nutrients was investigated in the Long Valley caldera of eastern California. Stream and spring waters were collected during the biologically-critical summer dry season when spring water/ground water inputs comprised >90% of streamflow. Samples were collected above and below major spring water inputs and irrigated pastures grazed by beef cattle to isolate the effects of spring waters versus cattle grazing as potential sources of riverine N and P. Inputs of N and P from geologic materials were identified as the primary source of elevated nutrient concentrations throughout the study area. Nitrogen, in the form of NO3–N (0.11–0.33 ​mg/L), originated from the slightly-thermal, shallow aquifer subsystem that intersected lacustrine/fluvial materials incorporating nitrogen-bearing geologic materials. Phosphorus, as PO4–P (0.132–0.255 ​mg/L), originated from both the shallow and deeper (thermal) groundwater systems and was attributed to its rapid release from weathering of the volcanic deposits. Grazing activities generated no discernible increases in mineral N or TP loads when comparing streamflow above and below grazed locations. There was a substantial loss of NO3–N during flood irrigation of pastures that was attributed to denitrification and/or vegetation uptake, with a corresponding increase of dissolved organic nitrogen ascribed to leaching of plant and/or fecal materials. This study demonstrates that geologically-derived nutrients (N and P) from volcanic terrains can be an important source of stream water nutrients. Results of this study are consistent with our previous results in volcanic areas of northern California and highlight that geologically-derived nutrients are often overlooked as a source of riverine nutrients and can have a profound effect on aquatic ecosystems.

An upper-crust lid over the Long Valley magma chamber.

Geophysical characterization of calderas is fundamental in assessing their potential for future catastrophic volcanic eruptions. The mechanism behind the unrest of Long Valley Caldera in California remains highly debated, with recent periods of uplift and seismicity driven either by the release of aqueous fluids from the magma chamber or by the intrusion of magma into the upper crust. We use distributed acoustic sensing data recorded along a 100-kilometer fiber-optic cable traversing the caldera to image its subsurface structure. Our images highlight a definite separation between the shallow hydrothermal system and the large magma chamber located at ~12-kilometer depth. The combination of the geological evidence with our results shows how fluids exsolved through second boiling provide the source of the observed uplift and seismicity.

Ages of the granitic basement of Long Valley Caldera, California, USA, and siting of the Quaternary granite-rhyolite pluton

The leucogranitic crystal-mush pluton beneath the iconic Long Valley Caldera, California, USA, released >820 km3 of crystal-poor Pleistocene rhyolite, which was hosted by numerous Mesozoic granitic plutons, only a few of which had been dated until now. Reported here are U-Pb zircon ages, determined by sensitive high-resolution ion microprobe−reverse geometry (SHRIMP-RG), for 11 circumcaldera granitoids, all of them either Triassic or Cretaceous. Growth of the 35-km-wide Quaternary rhyolite-leucogranite plutonic reservoir was fostered by collocation of (1) a dense swath of late Pliocene basaltic vents, (2) a left-stepping extensional reentrant in the rangefront fault zone of the Sierra Nevada batholith, and (3) a sharp offset of the Proterozoic continental margin as represented by the Sr-isotope 0.706 line. We further consider whether the basement architecture of as many as 26 separate Triassic and Cretaceous plutons and intervening septa and pendants of Paleozoic metasedimentary rocks influenced siting of the Quaternary pluton and whether the ragged margin of Proterozoic lithosphere helped to focus asthenospheric edge upwelling that intensified crustal melting and intrusion in both the Triassic and the Quaternary.

A complex patchwork of magma bodies that fed the Bishop Tuff supereruption (Long Valley Caldera, CA, United States): Evidence from matrix glass major and trace-element compositions

The geologic record reveals events in which enormous volumes (100–1000s of km3) of magma were erupted in a matter of days to months. Yet, the architecture of magmatic systems that feed supereruptions can only be investigated through the study of ancient systems. For more than 40 years, the Bishop Tuff (Long Valley, California) has been the archetypal example of a single, zoned magma body that fed a supereruption. Early-erupted material is pyroxene-free and crystal poor (< 20 wt%), presumably erupted from the upper parts of the magma body; late-erupted material is orthopyroxene and clinopyroxene-bearing, commonly more crystal rich (up to 30 wt% crystals), and presumably tapped magma from the lower portions of the magma body. Fe-Ti oxide compositions suggest higher crystallization temperatures for late-erupted magmas (as high as 820°C) than for early-erupted magmas (as low as 700°C). Pressures derived from major-element compositions of glass inclusions were used to suggest an alternative model of lateral juxtaposition of two main magma bodies—each one feeding early-erupted and late-erupted units. Yet, this interpretation has proven controversial. We present a large dataset of matrix glass compositions for 227 pumice clasts that span the stratigraphy of the deposit. We calculate crystallization pressures based on major-element glass compositions using rhyolite-MELTS geobarometry and crystallization temperatures based on Zr in glass using zircon-saturation geothermometry. Additionally, we apply the same methods to 1,538 major-element and 615 trace-element analyses from a dataset from the literature. The results overwhelmingly demonstrate that the variations in crystallization temperature and pressure are not consistent with vertical stratification of a single magma body. All crystallization pressures and temperatures are very similar, with modes of ∼150 MPa and ∼730°C. Our results support lateral juxtaposition of three main magma bodies. Magmas represented by smaller stratigraphic units crystallized at similar pressures as the main bodies, which suggests coexistence of larger and smaller magma bodies at the time of eruption. We compare our findings with results for other very large eruptions and supereruptions. We argue that supereruptions typically mobilize a complex patchwork of magma bodies that reside within specific levels of the crust. These eruptions reveal the architecture of the crust during moments of high abundance of eruptible magma, revealing crustal states that differ from what is inferred for magmatic systems currently present on Earth.

Geolocalization of Large-Scale DAS Channels Using a GPS-Tracked Moving Vehicle

Abstract Geolocalization of distributed acoustic sensing (DAS) array channels represents a crucial step whenever the technology is deployed in the field. Commonly, the geolocalization is performed using point-wise active-source experiments, known as tap tests, conducted in the vicinity of the recording fiber. However, these controlled-source experiments are time consuming and greatly diminish the ability to promptly deploy such systems, especially for large-scale DAS experiments. We present a geolocalization methodology for DAS instrumentation that relies on seismic signals generated by a geotracked vehicle. We demonstrate the efficacy of our workflow by geolocating the channels of two DAS systems recording data on dark fibers stretching approximately 100 km within the Long Valley caldera area in eastern California. Our procedure permits the prompt calibration of DAS channel locations for seismic-related applications such as seismic hazard assessment, urban-noise monitoring, wavespeed inversion, and earthquake engineering. We share the developed set of codes along with a tutorial guiding users through the entire mapping process.

Seasonal and Multiyear Changes in CO2Degassing at Mammoth Mountain Explained by Solid‐Earth‐Driven Fault Valving

AbstractChanges in CO2emissions from volcanoes may evidence volcanic unrest. We use a multiyear time series of CO2flux collected at the Horseshoe Lake Tree Kill area on Mammoth Mountain, CA, to understand processes that cause variations in flux from this system. Seasonal variations are systematically lowest during the winter months and reach maximum values during the summer season. A persistent ∼20% reduction in CO2flux occurred during the Spring of 2017, coincident with the emergence of the area from drought and earthquake swarms in Long Valley Caldera. We used continuous GNSS measurements to calculate seasonal strains and stresses across the Mammoth Mountain area, and resolved resultant stresses onto the Mammoth Mountain Fault, which appears to facilitate gas transport to the surface. The normal stress changes are consistent with seasonal and multiyear changes in CO2flux, suggesting that fault valving by solid earth processes can alter surface gas fluxes.

The Composition and Growth Mechanism of Coexisting 4M2 and 4A8 Biotite Polytypes from Rhyolite of Long Valley Caldera, California

AbstractPolytypism is common in micas, and the frequency of polytype occurrence is believed to be related closely to the crystallization conditions and chemical compositions of the corresponding fluids and melts. Coexisting multiple standard and complex/disordered polytypes in igneous rocks generally reflect a complicated magma evolution history. The purpose of the current study was to clarify the origin of coexisting biotite polytypes and their growth mechanism. Micro-X-ray diffraction (μXRD) and transmission electron microscopy (TEM) were used to investigate Fe-rich biotite phenocrysts in rhyolite from the Long Valley Caldera, California, USA. The μXRD analyses characterized various polytypes, and TEM observations revealed that common polytypes (e.g. 1M, 2M1, and 3T) and rare polytypes (e.g. 4M2 and 4A8) coexist within biotite monocrystals. The two 4-layer polytypes of Fe-rich biotite, 4M2 and 4A8, were identified via selected-area electron diffraction (SAED) and high-resolution scanning transmission electron microscopy (HRSTEM) at the atomic resolution, with unique stacking sequences ([0222] for 4M2 and [0022¯] for 4A8). Energy-dispersive X-ray spectroscopy (EDS) results showed differences in their chemical compositions, especially Fe and K. The 4A8 polytype is reported for the first time. The present study suggested that environmental changes, such as rapid cooling and inhomogeneous compositional distribution, led to chemical and structural oscillations and complex nucleation of the two 4-layer polytypes. Screw dislocations producing spiral growth enhance polytype stability and form ordered long-period/complex polytypes. These results are useful to understand the origin of long-period/complex polytypes and the intergrowths of diverse polytypes formed in non-equilibrium crystallization environments.

Fe3+/FeT ratios of amphiboles determined by high spatial resolution single-crystal synchrotron Mössbauer spectroscopy

Abstract The Fe3+/FeT ratios (Fe3+/[Fe2++Fe3+]) in minerals can be used to understand their crystallization and post-crystallization conditions. However, as natural minerals are often zoned and contain inclusions, bulk techniques, e.g., wet chemistry, may not provide accurate Fe3+/FeT values for a single phase of interest. We determined Fe3+/FeT ratios of amphiboles in different crystallographic orientations by single-crystal synchrotron Mössbauer spectroscopy (SMS) in energy and time domain modes from four volcanic localities (Long Valley Caldera, Mount St. Helens, Lassen Volcanic Center, U.S.A., and Mt. Pinatubo, Philippines). The high spatial resolution (as low as 12 × 12 μm spot size) and standard-free nature of SMS allow the detection of intra-grain compositional heterogeneities in Fe3+/FeT with relatively low uncertainties. We combine SMS with major element compositions, water contents, and hydrogen isotope compositions to document the Fe3+/FeT ratios as a function of mineral composition and post-crystallization dehydrogenation. Spectra were fitted with up to five distinct sites: ferrous iron on M(1), M(2), M(3), and ferric iron on M(2) and M(3), consistent with X-ray diffraction studies on single crystals of amphibole. The Fe3+/FeT ratios range from 0.14 ± 0.03 (Long Valley Caldera), 0.51 to 0.63 ± 0.02 (representing intra-grain heterogeneities, Mount St. Helens) to 0.86 ± 0.03 (Lassen Volcanic Center). The latter grain experienced post-crystallization dehydrogenation, shown by its low water content (0.6 ± 0.05 wt%) and its elevated hydrogen isotope composition (δD = +25 ± 3‰ relative to SMOW). The Fe3+/FeT ratios of 0.62 ± 0.01 and 0.20 ± 0.01 of two Mt. Pinatubo grains correlate with high-Al2O3 cores and low-Al2O3 rims and smaller phenocrysts in the sample, respectively. This study shows that SMS is capable of distinguishing two different domains with dissimilar Fe3+/FeT values formed under different crystallization conditions, demonstrating that SMS in combination with major element, water, and hydrogen isotope compositions allows the interpretation of amphibole Fe3+/FeT ratios in the context of crystallization and post-crystallization processes.

Toward Improving Point‐Source Moment‐Tensor Inference by Incorporating 1D Earth Model's Uncertainty: Implications for the Long Valley Caldera Earthquakes

AbstractTo infer seismic moment tensor (MT) of moderate earthquakes at regional scales, seismologists typically simulate waveforms using available structural models of the Earth to match the observed seismograms. This procedure is known as waveform seismic MT inversion. However, the seismic data are noisy, and the Earth model is inevitably different from the actual structure of the Earth; hence, there is a discrepancy between the predicted and the observed waveforms. This discrepancy arises from the noise in the data and imperfections in theoretical predictions, stemming most significantly from the Earth model. This study introduces structural uncertainty, estimated empirically, and referred to as “theory uncertainty,” as part of the combined covariance matrix. In the synthetic setting, we first show through a series of synthetic experiments that the structural uncertainty plays a critical role in retrieving MT solutions, especially for short‐period waveforms. The method is then benchmarked against the waveforms of non‐double‐couple earthquakes in Long Valley Caldera, California. We confirm the highly isotropic nature of the source in a pilot event but find a non‐negligible CLVD component that was overlooked in past studies ignoring the uncertainty in Earth model. Thus, careful consideration of the Earth model's uncertainty as part of the MT inversion schemes will be necessary for future applications to better understand the complicated physics of earthquake sources.

Origin of Compositional Gradients with Temperature in the High-SiO2 Rhyolite Portion of the Bishop Tuff: Constraints on Mineral–Melt–Fluid Reactions in the Parental Mush

Abstract The Bishop Tuff (BT), erupted from the Long Valley caldera in California, displays two types of geochemical gradients with temperature: one is related to magma mixing, whereas the other is found in the high-SiO2 rhyolite portion of the Bishop Tuff and is characterized by twofold or lower concentration variations in minor and trace elements that are strongly correlated with temperature. It is proposed that the latter zonation, which preceded phenocryst growth, developed as a result of mineral–melt partitioning between interstitial melt and surrounding crystals in a parental mush, from which variable melt fractions were segregated. To test this hypothesis, trends of increasing vs decreasing element concentrations with temperature (as a proxy for melt fraction), obtained from published data on single-clast pumice samples from the high-SiO2 rhyolite portion of the Bishop Tuff, were used to infer their relative degrees of incompatibility vs compatibility between crystals and melt in the parental mush. Relative compatibility values (RCVi) for all elements i, defined as the concentration slope with temperature divided by average concentration, are shown to be linearly correlated with their respective bulk partition coefficients (bulk Di). Mineral–melt partition coefficients from the literature were used to constrain the average stoichiometry of the crystallization/melting reaction in the parental mush: 32 % quartz + 34 % plagioclase + 31 % K-feldspar + 1·60 % biotite + 0·42 % titanomagnetite + 0·34 % ilmenite + 0·093 % allanite + 0·024 % zircon + 0·025 % apatite = 100 % liquid. The proportions of tectosilicates in the reaction (i.e. location of eutectic) are consistent with depths of melt segregation of ~400–550 MPa and an activity of H2O of ~0·4–0·6. Temperatures of <770–780 °C are constrained by allanite in the reaction. Evidence that a fluid phase was present in the parental mush is seen in the decreasing versus increasing H2O and CO2 contents with temperature in the segregated interstitial melt that formed the high-SiO2 rhyolite portion of the Bishop Tuff. The presence of an excess fluid phase, which strongly partitions CO2 relative to the melt, is required to explain the compatible behavior of CO2, whereas the fluid abundance must have been low to explain the incompatible behavior of H2O. Calculated degassing paths for interstitial melts, which segregated from the parental mush and ascended to shallower depths to grow phenocrysts, match published volatile analyses in quartz-hosted melt inclusions and constrain fluid abundances in the mush to be ≤1 wt%. The source of volatiles in the parental mush, irrespective of whether it formed by crystallization or partial melting, must have been primarily from associated basalts, as granitoid crust is too volatile poor. Approximately twice as much basalt as rhyolite is needed to provide the requisite volatiles. The determination of bulk Di for several elements gives the bulk composition of the parental leucogranitic mush and shows that it is distinct from Mesozoic Sierran arc granitoids, as expected. Collectively, the results from this study provide new constraints for models of the complex, multi-stage processes throughout the Plio-Quaternary, involving both mantle-derived basalt and pre-existing crust, that led to the origin of the parental body to the Bishop Tuff.

A New Analysis of Caldera Unrest through the Integration of Geophysical Data and FEM Modeling: The Long Valley Caldera Case Study

The Long Valley Caldera, located at the eastern edge of the Sierra Nevada range in California, has been in a state of unrest since the late 1970s. Seismic, gravity and geodetic data strongly suggest that the source of unrest is an intrusion beneath the caldera resurgent dome. However, it is not clear yet if the main contribution to the deformation comes from pulses of ascending high-pressure hydrothermal fluids or low viscosity magmatic melts. To characterize the nature of the intrusion, we developed a 3D finite element model which includes topography and crust heterogeneities. We first performed joint numerical inversions of uplift and Electronic Distance Measurement baseline length change data, collected during the period 1985–1999, to infer the deformation-source size, position, and overpressure. Successively, we used this information to refine the source overpressure estimation, compute the gravity potential and infer the intrusion density from the inversion of deformation and gravity data collected in 1982–1998. The deformation source is located beneath the resurgent dome, at a depth of 7.5 ± 0.5 km and a volume change of 0.21 ± 0.04 km3. We assumed a rhyolite compressibility of 0.026 ± 0.0011 GPa−1 (volume fraction of water between 0% and 30%) and estimated a reservoir compressibility of 0.147 ± 0.037 GPa−1. We obtained a density of 1856 ± 72 kg/m3. This density is consistent with a rhyolite melt, with 20% to 30% of dissolved hydrothermal fluids.

Basal nucleation and the prevalence of ascending swarms in Long Valley caldera.

Earthquake swarms are ubiquitous in volcanic systems, being manifestations of underlying nontectonic processes such as magma intrusions or volatile fluid transport. The Long Valley caldera, California, is one such setting where episodic earthquake swarms and persistent uplift suggest the presence of active magmatism. We quantify the long-term spatial and temporal characteristics of seismicity in the region using cluster analysis on a 25-year high-resolution earthquake catalog derived using leading-edge deep-learning algorithms. Our results show that earthquake swarms beneath the caldera exhibit enlarged families with statistically significant tendency for upward migration patterns. The ascending swarms tend to nucleate at the base of the seismogenic zone with a spatial footprint that is laterally constrained by the southern rim of the caldera. We suggest that these swarms are driven by the transport of volatile-rich fluids released from deep volcanic processes. The observations highlight the potential for extreme spatial segmentation of earthquake triggering processes in magmatic systems.

The 2011-2019 Long Valley Caldera inflation: New insights from separation of superimposed geodetic signals and 3D modeling

Increasingly accurate, and spatio-temporally dense, measurements of Earth surface movements enable us to identify multiple deformation patterns and highlight the need to properly characterize the related source processes. This is particularly important in tectonically active areas, where deformation measurement is crucial for monitoring ongoing processes and assessing future hazard. Long Valley Caldera, California, USA, is a volcanic area where frequent episodes of unrest involve inflation and increased seismicity. Ground- and satellite-based instruments show that volcanic inflation renewed in 2011, and is continuing as of early 2021. Additionally, Long Valley Caldera is affected by the large, but spatially and temporally variable, amounts of precipitation falling on the adjacent Sierra Nevada Range.The density and long duration of deformation measurements at Long Valley Caldera provide an excellent collection of data to decompose time-series and separate multiple superimposed deformation sources. We analyze Global Navigation Satellite System (GNSS) time-series and apply variational Bayesian Independent Component Analysis (vbICA) decomposition method to isolate inflation-related signals from other processes. We show that hydrological forcing causes significant horizontal and vertical deformation at different temporal (seasonal and multiyear) and spatial (few to hundreds of km) scales that cannot be ignored while analyzing and modeling the tectonic signal. Focusing on the last inflation episode, we then improve on prior simplistic models of the inflation reservoir by including heterogeneous subsurface material properties and topography. Our results suggest the persistence and stability of the reservoir (prolate ellipsoid at about 8 km beneath the resurgent dome) and indicate a 40-50% reduction of the inflation rate after about 3 years from the inflation onset. The onset of the reduced inflation rate corresponded in time with the occurrence of a strong seismic swarm in the Caldera, but also to the temporal variation of climatic conditions in the area.

Temperatures and water contents of Long Valley, CA basalts: Application of olivine–melt thermometry and hygrometry at the liquidus

The Plio-Quaternary Long Valley (LV) basalts, derived from subduction-modified lithosphere, are found in close proximity to the Long Valley caldera in California, from which hydrous high-SiO2 rhyolites were erupted, including the climactic Bishop Tuff (>600 km3). To better understand the processes by which the influx of basalts into the crustal column beneath Long Valley caldera led to the generation of voluminous high-SiO2 rhyolite, it is necessary to determine the range of temperatures and water contents of the LV basalts. In this study, olivine–melt thermometry and hygrometry are applied to several, high-MgO (~7–10 wt%) LV basalts which contain phenocrysts of olivine and clinopyroxene, many of which display diffusion-limited, rapid-growth textures. Histograms of analyzed olivine compositions display a continuous, unimodal population in each sample. When the most Mg-rich olivine in each sample is paired with a liquid composition that matches that for the whole-rock (and a Fe3+/FeT ratio of 0.24), Fe2+−MgKD (olivine–melt) values of 0.32–0.36 are obtained, consistent with preservation of the first olivine composition to crystallize near the liquidus due to rapid phenocryst growth during ascent. Both a Mg- and Ni-based olivine–melt thermometer from the literature, calibrated on the same experimental dataset, were applied to the most Mg-rich olivine paired with the whole-rock melt composition. Because the Ni-thermometer is independent of water content, it provides the actual temperature at the onset of olivine crystallization in each of the LV basalts (1198–1053 °C), whereas the Mg-thermometer gives the temperature under anhydrous conditions and thus allows ∆T (= TMg–TNi = depression of liquidus due to water) to be obtained. The average ∆T for all samples is 86 (±27) °C, which literature models show is consistent with an average melt water content of ~4.3 (±1.5) wt%.

The Economic Effects of Volcanic Alerts-A Case Study of High-Threat U.S. Volcanoes.

A common concern about volcanic unrest is that the communication of information about increasing volcanic alert levels (VALs) to the public could cause serious social and economic impacts even if an eruption does not occur. To test this statement, this study examined housing prices and business patterns from 1974-2016 in volcanic regions with "very-high" threat designations from the U.S. Geological Survey (USGS)-Long Valley Caldera (LVC), CA (caldera); Mount St. Helens (MSH), Washington (stratovolcano); and Kīlauea, Hawai'i (shield volcano). To compare economic trends in nonvolcanic regions that are economically dependent on tourism, Steamboat Springs, CO, served as a control as it is a ski-tourism community much like Mammoth Lakes in LVC. Autoregressive distributed lag (ARDL) models predicted that housing prices were negatively affected by VALs at LVC from 1982-1983 and 1991-1997. While VALs associated with unrest and eruptions included in this study both had short-term indirect effects on housing prices and business indicators (e.g., number of establishments, employment, and salary), these notifications were not strong predictors of long-term economic trends. Our findings suggest that these indirect effects result from both eruptions with higher level VALs and from unrest involving lower-level VAL notifications that communicate a change in volcanic activity but do not indicate that an eruption is imminent or underway. This provides evidence concerning a systemic issue in disaster resilience. While disaster relief is provided by the U.S. federal government for direct impacts associated with disaster events that result in presidential major disaster declarations, there is limited or no assistance for indirect effects to businesses and homeowners that may follow volcanic unrest with no resulting direct physical losses. The fact that periods of volcanic unrest preceding eruption are often protracted in comparison to precursory periods for other hazardous events (e.g., earthquakes, hurricanes, flooding) makes the issue of indirect effects particularly important in regions susceptible to volcanic activity.

A Novel Multidisciplinary Approach for the Thermo‐Rheological Study of Volcanic Areas: The Case Study of Long Valley Caldera

AbstractWe propose a novel multidisciplinary approach to image the thermo‐rheological stratification beneath active volcanic areas, such as Long Valley Caldera (LVC). We performed a thermal fluid dynamic model via optimization procedure of the thermal conditions of the crust. We characterize the topology of the hot magmatic bodies and the hot fluid circulation (the permeable fault‐zones), using both a novel imaging of the a and b parameters of the Gutenberg‐Richter law and an innovative procedure analysis of P‐wave tomographic models. The optimization procedure provides the permeability of a reservoir (5.0 × 10−14 m2) and of the fault‐zone (5.0 · 10−14 – 1.0 × 10−13 m2), as well as the temperature of the magma body (750–800°C). The imaging of the rheological properties of the crust indicates that the brittle/ductile transition occurs about 5 km b.s.l. depth, beneath the resurgent dome. There are again deeper brittle conditions about 15 km b.s.l., agreeing with the previous observations. The comparison between the conductive and the conductive‐convective heat transfer models highlights that the deeper fluid circulation efficiently cools the volumes above the magmatic body, transferring the heat to the shallow geothermal system. This process has a significant impact on the rheological properties of the upper crust as the migration of the B/D transition. Our findings show an active magmatic system (6–10 km deep) and confirm that LVC is a long‐life silicic caldera system.

Builders, tenants, and squatters: the origins of genetic material in modern stromatolites.

Micro-organisms have long been implicated in the construction of stromatolites. Yet, establishing a microbial role in modern stromatolite growth via molecular analysis is not always straightforward because DNA in stromatolites can have multiple origins. For example, the genomic material could represent the microbes responsible for the construction of the stromatolite (i.e., "builders"), microbes that inhabited the structure after it was built (i.e., "tenants"), or microbes/organic matter that were passively incorporated after construction from the water column or later diagenetic fluids (i.e., "squatters"). Disentangling the role of micro-organisms in stromatolite construction, already difficult in modern systems, becomes more difficult as organic signatures degrade, and their context is obscured. To evaluate our ability to accurately decipher the role of micro-organisms in stromatolite formation in geologically recent settings, 16/18S SSU rRNA gene sequences were analyzed from three systems where the context of growth was well understood: (a) an actively growing stromatolite from a silicic hot spring in Yellowstone National Park, Wyoming, where the construction of the structure is controlled by cyanobacteria; (b) a mixed carbonate and silica precipitate from Little Hot Creek, a hot spring in the Long Valley Caldera of California that has both abiogenic and biogenic components to accretion; and (c) a near-modern lacustrine carbonate stromatolite from Walker Lake, Nevada that is likely abiogenic. In all cases, the largest percentage of recovered DNA sequences, especially when focused on the deeper portions of the structures, belonged to either the tenant or squatter communities, not the actual builders. Once removed from their environmental context, correct interpretation of biology's role in stromatolite morphogenesis was difficult. Because high-throughput genomic analysis may easily lead to incorrect assumptions even in these modern and near-modern structures, caution must be exercised when interpreting micro-organismal involvement in the construction of accretionary structures throughout the rock record.

Multi-hazard perceptions at Long Valley Caldera, California, USA

Caldera systems such as Long Valley Caldera, California; Taupo, New Zealand; and Campi Flegrei, Italy, experience centuries to millennia without eruption, but have the potential for large eruptions. This raises questions about how local residents' behavioral responses to these low-probability high-consequence events differ from their responses to events, such as wildfires and earthquakes, that have higher probabilities. To examine this issue, a multi-hazard mail survey of 229 households explored perceptions of—and responses to—volcano, earthquake and wildfire hazards in the Long Valley Volcanic Region. Response efficacy was the only significant predictor of emergency preparedness, which suggests that hazard managers can increase household emergency preparedness by emphasizing this attribute of protective actions. In addition to response efficacy, expected personal consequences, hazard intrusiveness, and affective responses were all significantly related to information seeking. This indicates that hazard managers can also increase households’ information seeking about local hazards and appropriate protective actions by communicating the certainty and severity of hazard impacts (thus increasing expected personal consequences) and that they communicate this information repeatedly (thus increasing hazard intrusiveness) to produce significant emotional involvement (thus increasing affective response).