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USGS2021

A petrological and conceptual model of Mayon volcano (Philippines) as an example of an open-vent volcano

Mayon is a basaltic andesitic, open-vent volcano characterized by persistent passive degassing from the summit at 2463 m above sea level. Mid-size (<0.1 km3) and mildly explosive eruptions and occasional phreatic eruptions have occurred approximately every 10 years for over a hundred years. Mayon’s plumbing system structure, processes, and time scales driving its eruptions are still not well-known, despite being the most active volcano in the Philippines. We investigated the petrology and geochemistry of its crystal-rich lavas (~50 vol% phenocrysts) from nine historical eruptions between 1928 and 2009 and propose a conceptual model of the processes and magmatic architecture that led to the eruptions. The whole-rock geochemistry and mineral assemblage (plagioclase + orthopyroxene + clinopyroxene + Fe-Ti oxide ± olivine) of the lavas have remained remarkably homogenous (54 wt% SiO2,~4 wt% MgO) from 1928 to 2009. However, electron microscope images and microprobe analyses of the phenocrysts and the existence of three types of glomerocrysts testify to a range of magmatic processes, including long-term magma residence, magma mixing, crystallization, volatile fluxing, and degassing. Multiple mineral-melt geothermobarometers suggest a relatively thermally buffered system at 1050±25 °C, with several magma residence zones, ranging from close to the surface, through reservoirs at ~4–5 km, and as deep as ~ 20 km. Diffusion chronometry on >200 orthopyroxene crystals reveal magma mixing timescales that range from a few days to about 65 years, but the majority are shorter than the decadal inter-eruptive repose period. This implies that magma intrusion at Mayon has been nearly continuous over the studied time period, with limited crystal recycling from one eruption to the next. The variety of plagioclase textures and zoning patterns reflect fluxing of volatiles from depth to shallower melts through which they eventually reach the atmosphere through an open conduit. The crystal-rich nature of the erupted magmas may have developed during each inter-eruptive period. We propose that Mayon has behaved over almost 100 years as a steady state system, with limited variations in eruption frequency, degassing flux, magma composition, and crystal content that are mainly determined by the amount and composition of deep magma and volatile input in the system. We explore how Mayon volcano’s processes and working model can be related to other open-vent mafic and water-rich systems such as Etna, Stromboli, Villarrica, or Llaima. Finally, our understanding of open-vent, persistently active volcanoes is rooted in historical observations, but volcano behavior can evolve over longer time frames. We speculate that these volcanoes produce specific plagioclase textures that can be used to identify similar volcanic behavior in the geologic record.

Mayon volcano↗

USGS2022

Towards real-time probabilistic ash deposition forecasting for New Zealand

Volcanic ashfall forecasts are highly dependent on eruption source parameters (ESPs) and synoptic weather conditions at the time and location of the eruption. In New Zealand, MetService and GNS Science have been jointly developing an ashfall forecast system that incorporates four-dimensional high-resolution numerical weather prediction (NWP) and ESPs into the HYSPLIT model, a state-of-the art hybrid Eulerian and Lagrangian dispersion model widely used for volcanic ash. However, these forecasts are based on discrete ESPs combined with a deterministic weather forecast and thus provide no information on output uncertainty. This shortcoming hinders stakeholder decision making, particularly near the geographical margin of forecasted ashfall and in areas with large gradients in forecasted ash deposition. Our study presents a new approach that incorporates uncertainty from both eruptive and meteorological inputs to deliver uncertainty in the model output. To this end, we developed probability density functions (PDFs) for three key ESPs (plume height, mass eruption rate, eruption duration) tailored to New Zealand’s volcanoes and combine them with NWP ensemble datasets to generate probabilistic ashfall forecasts using the HYSPLIT model. We show that the Latin Hypercube Sampling (LHS) technique can be used to representatively span this four-dimensional parameter space and allow us to add uncertainty quantification to rapid response forecast systems. For a case study of a hypothetical eruption at Tongariro, New Zealand we suggest that large parts of New Zealand’s North Island would not receive adequate warning for potential ashfall if uncertainties were not included in the forecasts. We also propose new probabilistic summary products to support public information and emergency responders decision making.

Journal of Applied Volcanology↗

USGS2026

Growth and erosion of volcanic islands since 1963 analyzed by multi-sensor satellite data and historical records

Most volcanic activity is taking place in the oceans. Depending on water depth, eruption recurrence times and volumes, a new island can form. The power of erosional forces, the type of erupted material and the efficiency of secondary processes determine the island’s lifetime. Since the famous eruption of Surtsey (Iceland) in 1963, at least another 23 volcanic islands have appeared. Some islands remained intact for years or decades, whereas others disappeared within just weeks or months. In this study, we analyzed satellite data to determine growth and erosion rates of the volcanic edifices related to these 24 islands. We combined multi-sensor (optical, thermal, radar) satellite data time series with information from literature and the Global Volcanism Program database. We developed a comprehensive dataset, including 19 parameters, on the islands’ lifetime, shape, area, volume, eruption style and duration, environmental conditions, development of sedimentary deposits, and the geomorphic evolution of the island over time. Our dataset is available in a database format. This database allows us to test eight hypotheses about factors influencing the islands’ lifetime. Our results show that instead of one single critical factor, a combination of different factors influences the life history of volcanic islands. For instance, we show that larger islands do not necessarily live longer. The mechanical properties of the eruption products affect the island’s structural integrity. Irrespective of the material, a minimum initial area of around 50,000 m 2 seems to be a reasonable threshold to give the island a chance to exist longer.

Bulletin of Volcanology↗

USGS2026

Between quiescence and crisis: Hawaiian Volcano Observatory communication and response strategies on the Island of Hawaiʻi

Over the past two centuries, eruptions of Mauna Loa volcano have damaged infrastructure and destroyed several communities on the Island of Hawaiʻi. Future eruptions will impact existing population centers and critical infrastructure, which continue to grow each year. The U.S. Geological Survey Hawaiian Volcano Observatory has developed and practiced methods to promote eruption preparedness in communities on the Island of Hawaiʻi, particularly over the past three decades during which Mauna Loa was quiescent while Kīlauea volcano erupted frequently. Here, we summarize the observatory’s efforts to increase awareness of hazards associated with Hawaiian volcanoes and describe how lessons learned during responses to past volcanic crises on Kīlauea were applied prior to and during the 2022 Mauna Loa eruption, highlighting new response communication challenges encountered during the event. Additionally, we identify potential avenues for future communication/outreach on the Island of Hawaiʻi, such as expanding efforts in communities located in high-hazard areas and striving to be more culturally and linguistically inclusive in our communication techniques.

Hawaii↗

USGS2015

Geomorphic consequences of volcanic eruptions in Alaska: A review

Eruptions of Alaska volcanoes have significant and sometimes profound geomorphic consequences on surrounding landscapes and ecosystems. The effects of eruptions on the landscape can range from complete burial of surface vegetation and preexisting topography to subtle, short-term perturbations of geomorphic and ecological systems. In some cases, an eruption will allow for new landscapes to form in response to the accumulation and erosion of recently deposited volcaniclastic material. In other cases, the geomorphic response to a major eruptive event may set in motion a series of landscape changes that could take centuries to millennia to be realized. The effects of volcanic eruptions on the landscape and how these effects influence surface processes has not been a specific focus of most studies concerned with the physical volcanology of Alaska volcanoes. Thus, what is needed is a review of eruptive activity in Alaska in the context of how this activity influences the geomorphology of affected areas. To illustrate the relationship between geomorphology and volcanic activity in Alaska, several eruptions and their geomorphic impacts will be reviewed. These eruptions include the 1912 Novarupta–Katmai eruption, the 1989–1990 and 2009 eruptions of Redoubt volcano, the 2008 eruption of Kasatochi volcano, and the recent historical eruptions of Pavlof volcano. The geomorphic consequences of eruptive activity associated with these eruptions are described, and where possible, information about surface processes, rates of landscape change, and the temporal and spatial scale of impacts are discussed. A common feature of volcanoes in Alaska is their extensive cover of glacier ice, seasonal snow, or both. As a result, the generation of meltwater and a variety of sediment–water mass flows, including debris-flow lahars, hyperconcentrated-flow lahars, and sediment-laden water floods, are typical outcomes of most types of eruptive activity. Occasionally, such flows can be quite large, with flow volumes in the range of 10 7 –10 9 m 3 . A review of the lahars generated during the 2009 eruption of Redoubt volcano will illustrate the geomorphic impacts of lahars on stream channels and riparian habitat. Although much work is needed to develop a comprehensive understanding of the geomorphic consequences of volcanic activity in Alaska, this review provides a synthesis of some of the best-studied eruptions and perhaps will serve as a starting point for future work on this topic.

Alaska↗

USGS2022

Evidence for near-source nonlinear propagation of volcano infrasound from Strombolian explosions at Yasur Volcano, Vanuatu

Volcanic eruption source parameters may be estimated from acoustic pressure recordings dominant at infrasonic frequencies (< 20 Hz), yet uncertainties may be high due in part to poorly understood propagation dynamics. Linear acoustic propagation of volcano infrasound is commonly assumed, but nonlinear processes such as wave steepening may distort waveforms and obscure the sourcing process in recorded waveforms. Here we use a previously developed frequency-domain nonlinearity indicator to quantify spectral changes due to nonlinear propagation primarily in 80 signals from explosions at Yasur Volcano, Vanuatu. We find evidence for ≤ "> ≤ ≤ 10 −3 dB/m spectral energy transfer in the band 3–9 Hz for signals with amplitude on the order of several hundred Pa at 200–400 m range. The clarity of the nonlinear spectral signature increases with waveform amplitude, suggesting stronger nonlinear changes for greater source pressures. We observe similar results in application to synthetics generated through finite-difference wavefield simulations of nonlinear propagation, although limitations of the model complicate direct comparison to the observations. Our results provide quantitative evidence for nonlinear propagation that confirms previous interpretations made on the basis of qualitative observations of asymmetric waveforms.

Bulletin of Volcanology↗

USGS2025

The ghost plume phenomenon and its impact on zenith-facing remote sensing measurements of volcanic SO2 emission rates

A large source of error in SO 2 emission rates derived from mobile Differential Optical Absorption Spectroscopy (DOAS) of volcanic gas plumes is the uncertainty in atmospheric light paths between the sun and the instrument, particularly under non-ideal atmospheric conditions, such as the presence of low clouds. DOAS instruments measure the SO 2 column density along the effective light path, so changes to that pathway directly affect the measured SO 2 signal. Due to complex radiative transfer mechanisms when a cloud is between the DOAS viewing position and a volcanic plume, measured plumes can appear spatially offset from their true location, a phenomenon informally referred to as “ghost plumes.” In addition to the appearance of ghost plumes, DOAS measurements recorded in non-ideal conditions have poorly characterized errors and are often discarded, limiting the data available to characterize volcanic degassing. In this study we simulate the radiative transfer associated with zenith-facing mobile DOAS traverses using the McArtim radiative transfer model for scenarios when there is a cloud layer between the instrument and the volcanic plume. In total, 217 permutations of atmospheric optical conditions are considered with varying cloud opacities (AOD = 0, 1, 2, 4, 8, 20), plume opacities (AOD = 0, 1, 2, 4, 8), solar zenith angles (SZA = 1°, 30°, 60°), and cloud thicknesses (200, 400, 800 m). We first develop objective criteria for selecting SO 2 baseline absorption levels and plume spatial extents. The simulated plume traverses are then integrated to obtain the SO 2 cross-sectional burdens which, after multiplication with the wind speed, yield SO 2 emission rates. We find large modification in the shape of the modeled cross-sectional burdens even under translucent (low AOD) cloud conditions in our modeled scenarios. Despite modification of the plume shape, the presence of a low cloud layer is typically not a large source of error in the SO 2 cross-sectional burden or emission rate obtained from zenith-facing DOAS traverses. We find that all measured cross-sectional burdens simulated using an aerosol-free plume in the above conditions and SZA ≤ 30° are within ±25% of the true value.

Journal of Volcanology and Goethermal Research↗

USGS2006

The morphology and evolution of the Stromboli 2002-2003 lava flow field--An example of a basaltic flow field emplaced on a steep slope

The use of a hand-held thermal camera during the 2002–2003 Stromboli effusive eruption proved essential in tracking the development of flow field structures and in measuring related eruption parameters, such as the number of active vents and flow lengths. The steep underlying slope on which the flow field was emplaced resulted in a characteristic flow field morphology. This comprised a proximal shield, where flow stacking and inflation caused piling up of lava on the relatively flat ground of the vent zone, that fed a medial–distal lava flow field. This zone was characterized by the formation of lava tubes and tumuli forming a complex network of tumuli and flows linked by tubes. Most of the flow field was emplaced on extremely steep slopes and this had two effects. It caused flows to slide, as well as flow, and flow fronts to fail frequently, persistent flow front crumbling resulted in the production of an extensive debris field. Channel-fed flows were also characterized by development of excavated debris levees in this zone (Calvari et al. 2005). Collapse of lava flow fronts and inflation of the upper proximal lava shield made volume calculation very difficult. Comparison of the final field volume with that expecta by integrating the lava effusion rates through time suggests a loss of ~70% erupted lava by flow front crumbling and accumulation as debris flows below sea level. Derived relationships between effusion rate, flow length, and number of active vents showed systematic and correlated variations with time where spreading of volume between numerous flows caused an otherwise good correlation between effusion rate, flow length to break down. Observations collected during this eruption are useful in helping to understand lava flow processes on steep slopes, as well as in interpreting old lava–debris sequences found in other steep-sided volcanoes subject to effusive activity.

Stromboli, Sicily, Tyrrhenian Sea↗

USGS1993

Development of the 1990 Kalapana Flow Field, Kilauea Volcano, Hawaii

The 1990 Kalapana flow field is a complex patchwork of tube-fed pahoehoe flows erupted from the Kupaianaha vent at a low effusion rate (approximately 3.5 m3/s). These flows accumulated over an 11-month period on the coastal plain of Kilauea Volcano, where the pre-eruption slope angle was less than 2??. the composite field thickened by the addition of new flows to its surface, as well as by inflation of these flows and flows emplaced earlier. Two major flow types were identified during the development of the flow field: large primary flows and smaller breakouts that extruded from inflated primary flows. Primary flows advanced more quickly and covered new land at a much higher rate than breakouts. The cumulative area covered by breakouts exceeded that of primary flows, although breakouts frequently covered areas already buried by recent flows. Lava tubes established within primary flows were longer-lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply; tubes within breakouts were never reoccupied once the supply was interrupted. During intervals of steady supply from the vent, the daily areal coverage by lava in Kalapana was constant, whereas the forward advance of the flows was sporadic. This implies that planimetric area, rather than flow length, provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes. ?? 1993 Springer-Verlag.

Bulletin of Volcanology↗

USGS2025

Monitoring lava lake fluctuations and crater refilling with continuous laser rangefinders

The U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) has developed a new method to continuously monitor lava lake elevations. Since 2018, HVO has stationed a laser rangefinder on Kīlauea’s caldera rim. The instrument automatically measures lava lake elevation each second, with centimeter accuracy. A stream of elevation data flows to HVO’s database and public website, contributing a valuable channel to HVO’s volcano monitoring network. The data display is intuitive for users, providing essential information with a new level of clarity. HVO has used this method to track Kīlauea’s changing lava lake elevations over a series of eruptions, and the time series data show several volcanic processes: crater refilling, gas pistoning, lava lake surface behavior, and endogenous crater floor uplift. This technique is versatile, nimble, and easy to use. Continuous laser rangefinders may also prove useful for tracking lava lakes elsewhere, and for monitoring other hazards such as growing lava domes and debris flows.

Hawaii↗

USGS2017

Revised tephra volumes for Cascade Range volcanoes

Isopach maps from tephra eruptions from Mount St. Helens were reported in Carey et al. (1995) and for tephra eruptions from Glacier Peak in Gardner et al. (1998). For exponential thinning, the isopach data only define a single slope on a log thickness versus square root of area plot. Carey et al. (1995) proposed a model that was used to estimate a second slope, and volumes were presented in both studies using this model. A study by Sulpizio (2005) for estimating the second slope and square root of area where the lines intersect involves a systematic analysis of many eruptions to provide correlation equations. The purpose of this paper is to recalculate the volumes of Cascades eruptions and compare results from the two methods. In order to gain some perspective on the methods for estimating the second slope, we use data for thickness versus distance beyond the last isopach that are available for some of the larger eruptions in the Cascades. The thickness versus square root of area method is extended to thickness versus distance by developing an approximate relation between the two assuming elliptical isopachs with the source at one of the foci. Based on the comparisons made between the Carey et al. (1995) and Sulpizio (2005) methods, it is felt that the later method provides a better estimate of the second slope. For Mount St. Helens, the estimates of total volume using the Sulpizio (2005) method are generally smaller than those using the Carey et al. (1995) method. For the volume estimates of Carey et al. (1995), the volume of the May 18, 1980, eruption of Mount St. Helens is smaller than six of the eight previous eruptions. With the new volumes using the Sulpizio (2005) method, the 1980 eruption is smaller in volume than the upper end of the range for only three of the layers (Wn, Ye, and Yn) and is the same size as layer We. Thus the 1980 eruption becomes representative of the mid-range of volumes rather than being in the lower range.

Cascade Range volcanoes↗

USGS2022

Rock alteration mapping in and around fossil shallow intrusions at Mt. Ruapehu New Zealand with laboratory and aerial hyperspectral imaging

Diagnostic absorption features in hyperspectral data can be used to identify a specific mineral or mineral associations. However, it is unknown how accurate hyperspectral mapping can be for identifying alteration mineral compositions at the resolution required to describe structures such as fossil intrusions, or whether it can accurately quantify the alteration present. This study compared petrographic observation with visible, near-infrared (VNIR), and shortwave infrared (SWIR) hyperspectral remote sensing at laboratory- (centimetre-scale) and aerial- (metre-scale) scales to characterise the abundance of surface hydrothermal rock alteration in and around a shallow fossil intrusion on Pinnacle Ridge, Mt. Ruapehu, New Zealand. We classified a high-resolution aerial hyperspectral image to develop a new surface alteration map using Spectral Angle Mapper (SAM) algorithm. The petrographic thin-section and the laboratory and aerial hyperspectral imaging revealed a spectrum of hydrous alteration phases as indicated by the presence of an absorption feature at 2207 nm. Moderate correlation exists between the depth of the absorption feature at 2207 nm and the point counting-derived alteration percent values, indicating reliability of laboratory-based hyperspectral analytical methods. In contrast, aerial hyperspectral data failed to provide any clear correlations to field-mapped alteration using a band-depth approach, and we interpret this due to ‘oversampling’ of surface (supergene) alteration, spectral mixing, and sensor limitations (e.g., bandwidth, signal-to-noise ratio). The hyperspectral image-derived alteration map, created using supervised image classification, can loosely be translated to a geotechnical map where porosity and permeability play a major role in localizing hydrothermal fluid flow and the formation of alteration mineral associations.

Mt. Ruapehu↗

USGS2005

Real-time measurement of volcanic SO 2 emissions: Validation of a new UV correlation spectrometer (FLYSPEC)

A miniaturized, lightweight and low-cost UV correlation spectrometer, the FLYSPEC, has been developed as an alternative for the COSPEC, which has long been the mainstay for monitoring volcanic sulfur dioxide fluxes. Field experiments have been conducted with the FLYSPEC at diverse volcanic systems, including Masaya (Nicaragua), Poás (Costa Rica), Stromboli, Etna and Vulcano (Italy), Villarica (Chile) and Kilauea (USA). We present here those validation measurements that were made simultaneously with COSPEC at Kilauea between March 2002 and February 2003. These experiments, with source emission rates that ranged from 95 to 1,560 t d −1 , showed statistically identical results from both instruments. SO 2 path-concentrations ranged from 0 to >1,000 ppm-m with average correlation coefficients greater than r 2 =0.946. The small size and low cost create the opportunity for FLYSPEC to be used in novel deployment modes that have the potential to revolutionize the manner in which volcanic and industrial monitoring is performed.

Bulletin of Volcanology↗

USGS2016

Dimmuborgir: a rootless shield complex in northern Iceland

The origin of Dimmuborgir, a shield-like volcanic structure within the Younger Laxá lava flow field near Lake Mývatn, in northern Iceland, has long been questioned. New airborne laser mapping (light detection and ranging (LiDAR)), combined with ground-penetrating radar results and a detailed field study, suggests that Dimmuborgir is a complex of at least two overlapping rootless shields fed by lava erupting from the nearby Lúdentarborgir crater row. This model builds upon previous explanations for the formation of Dimmuborgir and is consistent with observations of rootless shield development at Kīlauea Volcano, Hawaii. The larger rootless shields at Dimmuborgir, 1–1.5 km in diameter, elliptical in plan view, &sim;30 m in height, and each with a 500-m-wide summit depression, were capable of storing as much as 2–3 × 10 6 m 3 of lava. They were fed by lava which descended 30–60 m in lava tubes along a distance of 3 km from the crater row. The height difference generated pressure sufficient to build rootless shields at Dimmuborgir in a timescale of weeks. The main summit depressions, inferred to be drained lava ponds, could have emptied via a 30-m-wide × 5-m-deep channel, with estimated effusion rates of 0.7–7 m 3 s −1 and minimum flow durations of 5–50 days. We argue that the pillars for which Dimmuborgir is famed are remnants of lava pond rims, at various stages of disintegration that formed during pond drainage.

Bulletin of Volcanology↗

USGS2013

A statistical analysis of the global historical volcanic fatalities record

A new database of volcanic fatalities is presented and analysed, covering the period 1600 to 2010 AD. Data are from four sources: the Smithsonian Institution, Witham (2005), CRED EM-DAT and Munich RE. The data were combined and formatted, with a weighted average fatality figure used where more than one source reports an event; the former two databases were weighted twice as strongly as the latter two. More fatal incidents are contained within our database than similar previous works; approximately 46% of the fatal incidents are listed in only one of the four sources, and fewer than 10% are in all four. 278,880 fatalities are recorded in the database, resultant from 533 fatal incidents. The fatality count is dominated by a handful of disasters, though the majority of fatal incidents have caused fewer than ten fatalities. Number and empirical probability of fatalities are broadly correlated with VEI, but are more strongly influenced by population density around volcanoes and the occurrence and extent of lahars (mudflows) and pyroclastic density currents, which have caused 50% of fatalities. Indonesia, the Philippines, and the West Indies dominate the spatial distribution of fatalities, and there is some negative correlation between regional development and number of fatalities. With the largest disasters removed, over 90% of fatalities occurred between 5 km and 30 km from volcanoes, though the most devastating eruptions impacted far beyond these distances. A new measure, the Volcano Fatality Index, is defined to explore temporal changes in societal vulnerability to volcanic hazards. The measure incorporates population growth and recording improvements with the fatality data, and shows prima facie evidence that vulnerability to volcanic hazards has fallen during the last two centuries. Results and interpretations are limited in scope by the underlying fatalities data, which are affected by under-recording, uncertainty, and bias. Attempts have been made to estimate the extent of these issues, and to remove their effects where possible. The data analysed here are provided as supplementary material. An updated version of the Smithsonian fatality database fully integrated with this database will be publicly available in the near future and subsequently incorporate new data.

Journal of Applied Volcanology↗

USGS2022

Revisiting the depth distribution of seismicity before and after the 2004–2008 eruption of Mount St. Helens

Hypocenter estimation at active volcanoes improves our understanding of their magmatic systems and indicates changing conditions at depth for continuously monitored volcanoes. The most active volcano in the Cascades Range, Mount St. Helens, has a multi-decadal earthquake catalog and it shows an apparent change in the depth distribution of seismicity before and after the 2004–2008 dome-building eruption and unrest sequence. We use two new resources to evaluate the accuracy of hypocenters and consequently the change in depth distribution of seismicity before and after the 2004–2008 eruption. First, we deployed a dense array of 136 three-component nodal seismographs for one month in 2017, including sub-arrays on the newly extruded dome and crater floor. Second, for events recorded during this month, we located their hypocenters using a three-dimensional (3D) wavefront-tracking location solver and a recently developed tomography model derived from active and passive source data. The relocated hypocenters are generally shallower and more concentrated beneath the crater compared to their catalog locations. The mean hypocenter movement from catalog locations is 2.86 km, with an averaged depth shift of 2.53 km upward. Comparison between 2017 hypocenters located using all of the available phase picks and those located using only the catalog picks from the permanent network suggests the improved hypocenters mostly resulted from the location solver and the 3D velocity model, with smaller changes due to the dense three-component array. Applying the same hypocenter estimation method to phase picks for all events from 1997 to 2004 and 2008–2021, we found a concentration of seismicity between sea level and ~ 1 km above it before and after the 2004–2008 eruption. The new results suggest that the seismogenic structure in the shallow magmatic system quickly re-equilibrated to its earlier state after the dome-building eruption.

Washington↗

USGS2001

Time-variation of hydrothermal discharge at selected sites in the Western United States: Implications for monitoring

We compiled time series of hydrothermal discharge consisting of 3593 chloride- or heat-flux measurements from 24 sites in the Yellowstone region, the northern Oregon Cascades, Lassen Volcanic National Park and vicinity, and Long Valley, California. At all of these sites the hydrothermal phenomena are believed to be as yet unaffected by human activity, though much of the data collection was driven by mandates to collect environmental-baseline data in acticipation of geothermal development. The time series average 19 years in length and some of the Yellowstone sites have been monitored intermittently for over 30 years. Many sites show strong seasonality but few show clear long-term trends, and at most sites statistically significant decadal-scale trends are absent. Thus, the data provide robust estimates of advective heat flow ranging from ~130 MW in the north-central Oregon Cascades to ~6100 MW in the Yellowstone region, and also document Yellowstone hydrothermal chloride and arsenic fluxes of 1740 and 15-20 g/s, respectively. The discharge time series show little sensitivity to regional tectonic events such as earthquakes or inflation/deflation cycles. Most long-term monitoring to date has focused on high-chloride springs and low-temperature fumaroles. The relative stability of these features suggests that discharge measurements done as part of volcano-monitoring programs should focus instead on high-temperature fumaroles, which may be more immediately linked to the magmatic heat source.

Journal of Volcanology and Geothermal Research↗

USGS2014

Pyroclast/snow interactions and thermally driven slurry formation. Part 1: Theory for monodisperse grain beds

Lahars are often produced as pyroclastic flows move over snow. This phenomenon involves a complicated interplay of mechanical and thermal processes that need to be separated to get at the fundamental physics. The thermal physics of pyroclast/snow interactions form the focus of this paper. A theoretical model is developed of heat- and mass transfer at the interface between a layer of uniformly sized pyroclasts and an underlying bed of snow, for the case in which there is no relative shear motion between pyroclasts and snow. A microscale view of the interface is required to properly specify boundary conditions. The physical model leads to the prediction that the upward flux of water vapor - which depends upon emplacement temperature, pyroclast grain size, pyroclast-layer thickness, and snow permeability - is sometimes sufficient to fluidize the pyroclasts. Uniform fluidization is usually unstable to bubble formation, which leads to vigorous convection of the pyroclasts themselves. Thus, predicted threshold conditions for fluidization are tantamount to predicted thresholds for particle convection. Such predictions are quantitatively in good agreement with results of experiments described in part 2 of this paper. Because particle convection commonly causes scour of the snow bed and transformation of the pyroclast layer to a slurry, there exists a 'thermal scour' process for generating lahars from pyroclastic flows moving over snow regardless of the possible role of mechanical scour.

Bulletin of Volcanology↗