Saint Helens Research Articles

Examining Infrasound Propagation at High Spatial Resolution Using a Nodal Seismic Array

AbstractInfrasound—acoustic waves in the atmosphere below 20 Hz—is a useful monitoring tool. Topography and atmospheric structure strongly control infrasound propagation, and at common source–receiver distances neither of these effects can be ignored when quantitative source constraints are sought. Detailed spatial measurements of the infrasound wavefield would inform propagation models and improve source estimates. However, the “large‐N” deployment strategy now well‐known in seismology has not yet been realized for infrasound studies. Here, we use the 900‐node seismic array from the 2014 Imaging Magma Under St. Helens (iMUSH) experiment as a proxy for a large‐N infrasound network, by leveraging acoustic–seismic coupled arrivals. The active‐source component of iMUSH consisted of 23 shallowly buried explosions around Mount Saint Helens volcano; these explosions produced epicentral infrasound recorded on the nodes. We find that the bulk presence of ground‐coupled infrasound on the nodes is controlled by wind noise and source–receiver distance, with observed arrivals for eight explosions. Explosions with the most extensive coupling produce complex spatial waveform patterns across the array. These patterns are related to both topographic and atmospheric propagation effects, as well as spatially variable site (coupling) effects. We compare our observations to simple topographic diffraction and high‐resolution wind advection models, and full‐wave numerical simulations. We find strong spatial correlations between (a) coupled arrival strength and modeled topographic obstruction and (b) coupled arrival time and along‐path winds. Our seismoacoustic analyses and results are applicable to other existing and future nodal seismic data sets and can expand the utility of such deployments.

Volcano Monitoring With Magnetic Measurements: A Simulation of Eruptions at Axial Seamount, Kīlauea, Bárðarbunga, and Mount Saint Helens

AbstractMonitoring of active volcanic systems is a challenging task due in part to the trade‐offs between collection of high‐quality data from multiple techniques and the high costs of acquiring such data. Here we show that magnetic data can be used to monitor volcanoes by producing similar data to gravimetric techniques at significantly lower cost. The premise of this technique is that magma and wall rock above the Curie temperature are magnetically “transparent,” but not stationary within the crust. Subsurface movements of magma can affect the crustal magnetic field measured at the surface. We construct highly simplified magnetic models of four volcanic systems: Mount Saint Helens (1980), Axial Seamount (2015–2020), Kīlauea (2018), and Bárðarbunga (2014). In all cases, observed or inferred changes to the magmatic system would have been detectable by modern magnetometers. Magnetic monitoring could become common practice at many volcanoes, particularly in developing nations with high volcanic risk.

The relationship between thermal spatial variability and mean temperature alters movement and population dynamics

AbstractThe importance of spatial and temporal environmental variation in shaping ecosystem dynamics is well appreciated, yet the ecological consequences of dynamic spatial variability, that is, the temporal patterning of spatial variation, remain unresolved. Here, we experimentally generate temporally fluctuating thermal environments that have either a negative, positive, or neutral relationship between the mean spatial environmental temperature and the degree of thermal spatial heterogeneity. We test the hypothesis that the timing of spatial variation relative to diel temperature cycles can meaningfully alter movement patterns and population dynamics, using the motile green algae Chlamydomonas reinhardtii. Our results indicate that C. reinhardtii individuals growing in environments with positive relationships between spatial variability and mean temperature show reduced population growth rates, more directed movement as indicated by a reduced turning angle, and decreased negative thermotaxis over time, relative to those growing in environments with a negative relationship between spatial variability and mean temperature. We additionally document substantial regional variation in the dynamics of natural spatial variability by collecting summer water temperature measurements from five ponds in the Mount Saint Helens watershed, WA, USA. Our results collectively suggest that the dynamics of spatial variation are an underappreciated but salient feature within the broader interwoven fabric of spatiotemporal variation.

Thermal storage conditions and origin of compositional diversity of plagioclase crystals in magmas from the 1980 and 2004-2005 eruptions of Mount Saint Helens

Abstract The thermal histories of upper crustal magma reservoirs place important constraints on the formation, evolution, and remobilization of crustal magmas, yet quantifying thermal histories remains challenging. We report new in-situ plagioclase trace-element data, Sr in plagioclase diffusion timescales, and plagioclase 238U-230Th-226Ra disequilibria data from Mount Saint Helens (MSH) 1980 cryptodome and 2004-2005 dacite domes to evaluate the thermal storage conditions and compositional diversity of recent MSH magmas. This approach allows us to more directly link the thermal (and therefore physical) conditions within the MSH magma reservoir to timescales of storage, thereby constraining the fraction of time 1980-2005 MSH magmas have spent in a mobile state. Plagioclase trace-element data and U-series characteristics reveal a compositionally heterogenous magmatic system beneath MSH and also require multi-stage plagioclase growth histories. The data also show that 2004-05 dacites contain a different plagioclase population relative to the 1980 cryptodome dacite, comprised of either a compositionally (and possibly temporally) distinct plagioclase component or composed of the same plagioclase components but in significantly different proportions. Discordant plagioclase 238U-230Th and 230Th-226Ra apparent ages require a mixture of young (likely eruption related) and old (>20-40 ka) plagioclase crystals in both 1980 and 2004-05 dacites. The low (230Th)/(232Th) in all measured 1980 and 2004-05 plagioclase requires a significant fraction (>10-30%) of the plagioclase to be old (>10s kyr). Maximum modeled Sr diffusion timescales at 750oC range from decades to centuries for both eruptions, with a maximum of ~600 years found in 1980 cryptodome plagioclase. However, partially equilibrated Sr in the innermost exposed parts of some crystals found in both 1980 and 2004-05 plagioclase indicate that a fraction (>20%) of plagioclase may have experienced a total of >10 kyrs at temperatures ≥750oC. Coupling Sr diffusion timescales with U-series measurements indicates that significant fraction (at least ~40%) of modeled MSH plagioclase spent <5% of their storage time at temperatures ≥750oC and thus in an easily mobilized rheological state. In contrast, the fraction of partially equilibrated plagioclase possibly spent >25-50% of their storage time at hotter conditions. Our data combined with data from other arc magmatic systems (e.g., Mt. Hood) imply that the process of remobilizing magma in arc systems towards successive eruptions requires thermally rejuvenating largely crystalline material, as opposed to sequential tapping of a persistent liquid-dominated magma body, even if successive eruptions are spaced closely in time (decades). In addition, rejuvenation events responsible for successive eruptions may sample spatially localized, but potentially overlapping, portions of the broader magma reservoir.

Geophysical Challenges for Future Satellite Gravity Missions: Assessing the Impact of MOCASS Mission

The GRACE/GRACE-FO satellites have observed large scale mass changes, contributing to the mass budget calculation of the hydro-and cryosphere. The scale of the observable mass changes must be in the order of 300 km or bigger to be resolved. Smaller scale glaciers and hydrologic basins significantly contribute to the closure of the water mass balance, but are not detected with the present spatial resolution of the satellite. The challenge of future satellite gravity missions is to fill this gap, providing higher temporal and spatial resolution. We assess the impact of a geodetic satellite mission carrying on board a cold atom interferometric gradiometer (MOCASS: Mass Observation with Cold Atom Sensors in Space) on the resolution of simulated geophysical phenomena, considering mass changes in the hydrosphere and cryosphere. Moreover, we consider mass redistributions due to seamounts and tectonic movements, belonging to the solid earth processes. The MOCASS type satellite is able to recover 50% smaller deglaciation rates over a mountain range as the High Mountains of Asia compared to GRACE, and to detect the mass of 60% of the cumulative number of glaciers, an improvement respect to GRACE which detects less than 20% in the same area. For seamounts a significantly smaller mass eruption could be detected with respect to GRACE, reaching a level of mass detection of a submarine basalt eruption of 1.6 109 m3. This mass corresponds to the eruption of Mount Saint Helens. The simulations demonstrate that a MOCASS type mission would significantly improve the resolution of mass changes respect to existing geodetic satellite missions.

Decoding pyroclastic density current flow direction and shear conditions in the flow boundary zone via particle-fabric analysis

One of the greatest challenges in volcanology is extracting information from volcanic deposits that inform the conditions at the time of emplacement. Here we explore particle-shape fabric within samples from the column-collapse pyroclastic density current (PDC) deposits generated by the 18 May 1980 eruption of Mt. Saint Helens (MSH). Particle shape-fabric is the mutual alignment of particles within a sample, which is dependent on shearing conditions at the time of deposition. Here, particle shape-fabric is used to address the following hypotheses: (1) particle shape-fabric will align with bulk flow direction estimates made by previous studies, while resolving fine scale flow direction variations; (2) samples extracted from PDC deposits immediately above a basal contact will show higher extents of fabric development (i.e. clast alignment) relative to samples extracted well above the contact; and (3) samples extracted from cross-stratified deposits will have higher extents of fabric development relative to samples extracted from the massive facies. We find that fabric orientations approximate previous flow direction interpretations of general flow, from south to north, and channelization due to paleo-topography. Furthermore, shape-fabric records flow interaction with the substrate, created by debris avalanche deposits, leading to fine scale variations in flow paths. These variations are recorded in samples extracted near the substrate-deposit contact. Moreover, these samples do not show a higher measure of clast alignment relative to samples taken well above flow contacts but do exhibit bimodal clast alignment. This suggests some degree of traction transport and thus higher shearing conditions relative to when the currents deposited massive lapilli tuffs. Samples extracted from the cross-stratified deposits do not show higher extents of fabric development relative to the massive deposits, supporting previous interpretations that these deposits formed from a rapidly sedimenting, concentrated flow boundary zone that was thin enough to be frequently interrupted or influenced by the overriding turbulent portion of the flow. Finally, observations of fine scale variability in measured fabric within a single outcrop indicates unsteady flow conditions and step-wise aggradation during deposition. This work demonstrates that particle shape-fabric analyses can aid in decoding PDC flow conditions. Future complementary experimental work may allow for the extraction of quantitative information regarding the magnitudes of shear and subsequent particle alignments within the flow boundary zone, providing further insight into PDC dynamics.

GeoGirls: Confidence Erupts from a Camp at a Volcano

Summer camp at Mount Saint Helens empowers girls with science, confidence, and fun.

Mammalian community response to historic volcanic eruptions

It is clear that ecosystems are devastated after a volcanic eruption coats the landscape with a layer of ash; however, the ecological recovery of mammalian communities after eruptions is poorly understood. Volcanic eruptions vary with magnitude and type and only a fraction of them have been analysed for effects on mammalian communities. To better understand mammalian community recovery, I investigated how species richness, evenness, and similarity change across volcanic boundaries in the 1980 Mount Saint Helens (MSH), Washington, and 1914–1917 Mount Lassen, California, eruptions. I compared these eruptions to Mount Rainier, Washington and Mount Shasta, California as controls for regional changes in the fauna. Richness and evenness remain relatively unchanged in Lassen. MSH saw an immediate drop in richness, followed by an increase over 5 years to pre-eruptive levels. Chord distance analysis suggests no long-term change in the Lassen fauna. The pre- and post-MSH fauna are different from one another. The post-eruptive fauna was more similar to neighbouring regions. It is clear from my results that larger eruptions tend to have a greater impact on mammalian community recovery than smaller eruptions, but ultimately, mammalian populations are robust and the presence of neighbouring communities is important for recolonizing devastated areas.

Fragility Assessment of Vinyl Greenhouses and Livestock Sheds Subjected to Volcanic Ash Fall Hazards

In this study, fragility functions are developed to estimate expected volcanic ash damage to vinyl greenhouses and livestock sheds among common agricultural facilities in South Korea. The fragility functions are derived through the FOSM (first-order second-moment) analytical approach based on the thickness distribution of volcanic ash observed in the 1980 eruption of Mt. Saint Helens in the USA and on agricultural facility codes and specifications in South Korea. In this study, the volcanic ash fragility functions evaluated represent the conditional probability of failure of vinyl greenhouses and livestock sheds over the full range of volcanic ash loads. For the evaluation, 4 types (i.e., automated, single span, tree crop, and double span types) of multi-hazard resisting vinyl greenhouses and 3 types (i.e., standard, coastal, and mountain types) of livestock sheds conventionally utilized in South Korea are considered. All volcanic ash fragility functions estimated in this study are fitted using parameters of the lognormal CDF (cumulative distribution function), and the obtained parameters are compiled into a database for use in the future. The volcanic ash fragility functions developed in this study are intended to be used to evaluate potential risks and losses from volcanic eruptions around the Korean Peninsula.

Effects of fresh and aged vehicular exhaust emissions on breathing pattern and cellular responses – pilot single vehicle study

The study presented here is a laboratory pilot study using diluted car exhaust from a single vehicle to assess differences in toxicological response between primary emissions and secondary products resulting from atmospheric photochemical reactions of gas phase compounds with O3, OH and other radicals. Sprague Dawley rats were exposed for 5 h to either filtered room air (sham) or one of two different atmospheres: (i) diluted car exhaust (P)+Mt. Saint Helens Ash (MSHA); (ii) P+MSHA+secondary organic aerosol (SOA, formed during simulated photochemical aging of diluted exhaust). Primary and secondary gases were removed using a nonselective diffusion denuder. Continuous respiratory data was collected during the exposure, and bronchoalveolar lavage (BAL) and complete blood counts (CBC) were performed 24 h after exposure. ANOVA models were used to assess the exposure effect and to compare those effects across different exposure types. Total average exposures were 363 ± 66 μg/m3 P+MSHA and 212 ± 95 µg/m3 P+MSHA+SOA. For both exposures, we observed decreases in breathing rate, tidal and minute volumes (TV, MV) and peak and median flows (PIF, PEF and EF50) along with increases in breathing cycle times (Ti, Te) compared to sham. These results indicate that the animals are changing their breathing pattern with these test atmospheres. Exposure to P+MSHA+SOA produced significant increases in total cells, macrophages and neutrophils in the BAL and in vivo chemiluminescence of the lung. There were no significant differences in CBC parameters. Our data suggest that simulated atmospheric photochemistry, producing SOA in the P+MSHA+SOA exposures, enhanced the toxicity of vehicular emissions.

Cataclastic production of volcanic ash at Mount Saint Helens

The 2004–2008 eruption of Mt. St. Helens (MSH) produced a series of lava domes and spines distinguished by the occurrence of an enveloping carapace of finely comminuted, weakly indurated fault gouge. The fault gouge results from fracture and shear strain, causing comminution of dacite along the conduit walls during ascent. The faulting associated with the formation of gouge is assumed to be the origin of a repetitive microseismicity (i.e., “drumbeat” seismicity) sourced at ∼0.5–1km depth. The early phases of dome extrusion were attended by several small explosive events producing plumes of volcanic ash derived largely from the fault gouge.Here we present experimental results that establish the requisite conditions for this cataclastic production of volcanic ash at MSH. The experiments are low temperature rock deformation experiments performed on MSH dacite under confining pressures consistent with conduit pressures (0.1, 25, 50, 75MPa). The first set of experiments ended once a through-going shear fracture was formed; these produced a highly localized fault surface and associated fault gouge. A second set of experiments allowed frictional sliding along the fault surface after failure thereby exploring the role of shear strain on grain size reduction of the gouge.Rock strength increases with confining pressure (from 139 to 722MPa at 0.1 to 75MPa). Unconfined loading of the MSH dacite produced several longitudinal fractures with little gouge and a small stress drop (∼120MPa), whereas 75MPa experiments produced a near-linear shear fracture, with a stress drop of ∼300MPa. The amount of gouge and the grain size distribution of the gouge are only weakly affected by the confining pressure. Continued sliding (i.e., shear strain) causes a substantial increase in the amount of gouge but does not increase the number abundance of the finest (<10μm) particles. Thus, the finest particles are an expression only of the magnitude of the stress drop event (fracture) and not the shear strain during frictional sliding. The frictional sliding experiments elucidate the coefficient of friction – all confined experiments show stable slip and strain hardening with a slight increase in coefficient of friction from 0.48 to 0.55, with increased confining pressure. The unconfined sample shows a very low apparent coefficient of friction of ∼0.17.These results allow us to postulate the following ideas concerning the production of volcanic ash by syn-eruptive cataclasis. The significant stress drop, that produces abundant fine ash-sized particles, demands a material that can store substantial elastic energy prior to failure. Highly crystallized, low porosity magma, such as that found at MSH, and favoured by lower ascent rates, is ideal. More rapid ascent and extrusion of lava domes will result in less crystallized and more porous lava; such materials are much less likely to support the cataclastic production of ash sized gouge.

New stratigraphic markers in the late Pleistocene Palouse loess: novel fossil gastropods, absolute age constraints and non-aeolian facies

Four stratigraphic sections in the southern part of the Columbia Basin preserve a sequence of aeolian and non-aeolian sediments ranging in age from 9AE43 to >47AE0 14 C ka based on accelerator mass spectrometry radiocarbon dating of fossil molluscs, geochemistry of Cascade Mountain-sourced tephra and association with formally recognized pedostratigraphic units (the Washtucna and Old Maid Coulee soils). Study sections are interpreted as representing concurrent deposition of loess and distal Missoula Flood rhythmites in valleys tributary to main drainages backflooded during the Missoula Floods, and formation of carbonate and iron-rich soils. Sediments belong to the formally recognized L-1 and L-2 loess units established for the Palouse loess, which were deposited in the Columbia Basin subsequent to events of glacial outburst flooding. Sediments associated with the Mount Saint Helens set S and set C tephras in the study sections preserve a fauna of five species of gastropod mollusc which have not been reported previously from sediments of late Pleistocene age in the Palouse region. The fossils comprise two distinct faunules stratigraphically separated by the Mount Saint Helens So tephra. Accelerator mass spectrometry radiocarbon dating of the fossils collected above the tephra in two of the sections yielded ages of 12AE48 ± 0AE06 and 9AE43 ± 0AE05 14 C kyr. These ages suggest that independent determinations of the 13AE35 14 C kyr age of the So tephra in other areas where Missoula Flood sediments are preserved are probably accurate, and help to refine the age of the latest events in the most recent sequence of catastrophic glacial outburst flooding.

Global dimming and brightening versus atmospheric column transparency, Europe, 1906–2007

Multiannual changes in atmospheric column transparency based on measurements of direct solar radiation allow us to assess various tendencies in climatic changes. Variability of the atmospheric integral (broadband) transparency coefficient, calculated according to the Bouguer‐Lambert law and transformed to a solar elevation of 30°, is used for two Russian locations, Pavlovsk and Moscow, one Ukrainian location, Feodosiya, and three Estonian locations, Tartu, Tõravere, and Tiirikoja, covering together a 102‐year period, 1906–2007. The comparison of time series revealed significant parallelism. Multiannual trends demonstrate decrease in transparency during the postwar period until 1983/1984. The trend ends with a steep decline of transparency after a series of four volcanic eruptions of Soufriere (1979), Saint Helens (1980), Alaid (1981), and El Chichón (1982). From 1984/1985 to 1990 the atmosphere remarkably restored its clarity, which almost reached again the level of the 1960s. Following the eruption of Mount Pinatubo (June 1991), there was the most significant reduction in column transparency of the postwar period. However, from the end of 1990s, the atmosphere in all considered locations is characterized with high values of transparency. The clearing of the atmosphere (from 1993) evidently indicates a decrease in the content of aerosol particles and, besides the decline of volcanic activity, may therefore be also traced to environmentally oriented changes in technology (pollution prevention), to general industrial and agricultural decline in the territory of the former USSR and Eastern Europe after deep political changes in 1991, and in part to migration of some industries out of Europe.

Particulate kinematic simulations of debris avalanches: interpretation of deposits and landslide seismic signals of Mount Saint Helens, 1980 May 18

SUMMARY We construct a new class of granular landslide models in which avalanches are simulated with large numbers of independent particles moving under the influence of topographically derived gravitational and centripetal acceleration. Concurrently, the particles suffer deceleration due to basal and dynamic friction. The novel aspect of the calculation is that complex particle-toparticle interactions, fluctuating basal contacts, and unresolved topographic roughness within and below the deforming flow are mimicked by random perturbations in along-track and cross-slope acceleration. We apply the method to the 1980 May 18 Mount Saint Helens debris avalanche by constraining the initial geometry and structure of the slide mass from geological data, and the initial failure sequence from eyewitness accounts. After tuning coefficients of mechanical friction and random accelerations, the landslide simulation generates a final deposit whose extent, thickness, morphological structure and lithological variation closely replicate those observed. Moreover, the model avalanche is consistent kinematically with mapped patterns of bedrock scouring, deposit superelevation, and net force history implied from seismic records. To be successful, the slide mass must be divided into upper, high-friction and lower, low-friction members. This division corresponds to fresh, water-unsaturated and hydrothermally altered, water-saturated rock units and points to a mechanical explanation of the kinematics of the debris avalanche. Success in reproducing many features of the Mount Saint Helens avalanche indicates that debris-deposit data may be used to determine the kinematic histories of less well-observed landslides.

A Monitoring Project for Performance Evaluation of Transparent Honeycomb Insulation

To evaluate the performance of Transparent Honeycomb Insulation (THI), a monitoring program was carried out at Saint Helens (UK). The Northwest and Southeast facades of an existing terraced house were clad with honeycomb transparent insulation. Various heating and energy flow variables were monitored within this Transparently Insulated House (TIH) and in an adjoining Non-insulated House (NIH), which was a mirror image of the TIH. A computer program for the acquisition, storage and processing of data was developed. The accuracy of the monitored parameters was affected by the presence of high frequency electromagnetic waves in the area. This problem was reduced to an acceptable level by close monitoring of the instruments. Data measurement was plagued by excessive noise. Remedial techniques were adapted for dealing with these problems. The results show that in cold climates, THI increases the solar gain to the building and reduces the heat loss from envelop of the building. This provides a strong case for the viability of Transparent Honeycomb Insulation as an effective passive solar technology.

Permeability of vesicular silicic magma: inertial and hysteresis effects

Abstract The permeability of crystal-poor obsidian flow and pumice samples from Medicine Lake Volcano, USA, are measured to assess (1) the existence of a critical vesicularity (porosity) below which low crystallinity magma is effectively impermeable, (2) the effects of bubble texture on permeability, and (3) the importance of inertial effects in resisting fluid flow through magma. Consistent with prior studies, the Medicine Lake data indicate that fluids can readily percolate through magma with porosities greater than 65%. However, we find no abrupt decrease in permeability below 60% porosity, as found previously for low crystallinity samples of similar origin from Obsidian Dome, USA. Rather, the permeabilities of Medicine Lake samples show a gradual increase with increased vesicularity similar to that observed in highly crystalline samples from Soufriere Hills Volcano, Montserrat, and Mount Saint Helens, USA. We suggest that both vesicle microstructure and resulting porosity–permeability relationships depend on the deformation, decompression and degassing history of the magma. In particular, bubble deformation by shear and/or partial bubble collapse allows open-system degassing of magma with vesicularity of 20%, and perhaps lower. Permeability determines the rate at which samples can degas during decompression. Air flow rates through lava and pumice samples are not proportional to the pressure gradients driving flow, indicating that inertial effects are significant at laboratory conditions. Flow resistance from both inertial and viscous effects generally decreases with increasing porosity, and inertial effects are smaller for coarsely vesicular lava than for finely vesicular lava or pumice (tephra) samples with similar viscous (Darcian) permeabilities. For an H2O fluid at 800 °C and 25 MPa, the critical average fluid speed at which inertial and viscous effects are predicted to be comparable is between 10−4 and 10−1 m/s for all the Medicine Lake samples. As flow rates in this range are anticipated for volcanic eruption conditions, inertial effects should be considered in models of magma degassing at depth.

Size of Popocatepetl Volcano explosions (1997–2001) from waveform inversion

Several volcanic explosions have been recorded since April 1997 at broadband seismic stations located around the Popocatepetl volcano, Mexico. We have inverted waveforms of ten of these explosions to estimate the following source parameters: depth, duration, magnitude and direction of the single force, F. The crustal structure used in generating Green's function at nearest stations is derived from the inversion of teleseismic receiver functions at the broadband permanent station PPIG, located 5 km north of the volcano. This inversion reveals a low velocity zone at ∼8 km beneath the summit with high Poisson ratio, possibly related to the magma chamber. We find that F scales with τ, the duration of the source‐time function, as F ∝ tau². Based on this relationship we determine an impulse magnitude scale, Mk. This magnitude is tied to the Mount Saint Helens initial explosive phase of May 18, 1980, whose magnitude is estimated as 4.6. Mk of the ten Popocatepetl explosions ranges between 1.8 and 3.2. Finally, we also propose an equivalent formula for rapid estimation of magnitude of future Popocatepetl explosions, which requires filtered amplitudes at PPIG.

Doing Fieldwork in the Mud

********** I study mud, an activity that confirms the apprehensions of some of my human-geography colleagues. Mud in lakes, as opposed to mud underfoot, is composed mostly of microscopic plant and animal remains and finely ground rock materials that have accumulated over thousands of years. For that reason mud is highly variable in color, feel, and even smell, and the information it contains is influenced by its geographical location and age. There is a growing need to understand how the environment has changed over time, and gaining this knowledge can be approached in a number of ways. One way is to do fieldwork. Originally, going into the field meant collecting detailed observations to describe the physical world and its operation. Now, most field data are collected with a more directed purpose; namely, to test conceptual and numerical models of how the environment has changed in the past and may change in the future. My own interest in environmental change concerns the development of western North American forests and their sensitivity to past climate changes. This information comes from lakes and bogs, whose mud captures the pollen of nearby plants, charcoal from fires, and other organic and inorganic matter produced in the lake and watershed. Over time, lakes accumulate and preserve a thick sequence of sediments in a relatively undisturbed state. A core drilled vertically through these layers of mud retrieves a record that can extend back in time to the origination of the lake. Pollen, produced by flowering plants, are the primary data that I use for understanding past environments. Pollen grains are distinctive and identifiable under the microscope (at least to the taxonomic level of plant family), and variations in pollen composition disclose changes in the vegetation through time. Charcoal is produced during fires and carried aloft before settling on the ground and lake surface. In the sediments, layers with abundant charcoal particles are evidence of past fires and provide a basis for calculating changes in fire frequency through time. The chronology to support the environmental history is obtained using the radiocarbon dating method, which determines the age of small pieces of organic material preserved within the core. A seed or a small piece of wood is sufficient for a radiocarbon lab to make an age determination. In the western United States, volcanic ashes from Pacific Northwest volcanoes, including Mount Saint Helens, Glacier Peak, and Mount Mazama, are regularly found in lake sediments. These ash layers are distinguished by their geochemistry and can be traced to particular eruptions in the past. Their occurrence in the sedimentary record provides a useful dating tool to supplement radiocarbon dating. For example, as a result of the eruption of Mount Mazama (now the location of Crater Lake) about 7,600 years ago, Mazama ash is recovered in nearly every lake and wetland in the northwestern United States. The methodological approaches that underlie paleoecological fieldwork are often different from those used in modern bio geographical research. First, paleoecologists are limited to studying those components of ecosystems that are preserved as fossils, whereas most biogeographers have the luxury of designing a study that can examine and sample broadly from the natural environment. As an illustration of this limitation, it is difficult to study the paleohistory of aspen groves, even though knowledge of their past distributions would help address important management questions in the Rocky Mountains. The difficulty lies in an aspen grove's small production of pollen; furthermore, what is produced degrades easily and is not well preserved in the sedimentary record. Second, many biogeographical and ecological studies are based on an experimental design that allows conclusions to be drawn on the basis of repeated observations. Paleoecological research is not experimental. …

Residual Oil Fly Ash Induces Cytotoxicity and Mucin Secretion by Guinea Pig Tracheal Epithelial Cells via an Oxidant-Mediated Mechanism

Inhalation of ambient air particulate matter (PM) is associated with pulmonary injury and inflammation. Using primary cultures of guinea pig tracheal epithelial (GPTE) cells as an in vitro model of airway epithelium, we examined effects of exposure to suspensions of six different emission and ambient air PM samples: residual oil fly ash (ROFA) from an electrical power plant; fly ash from a domestic oil burning furnace (DOFA); ambient air dust from St. Louis (STL), Ottawa (OT), and Washington, DC (WDC); and volcanic ash from the eruption of Mount Saint Helens (MSH) in 1980. Effects of these particulates on cell viability (assessed via LDH assay), secretion of mucin (measured by a monoclonal antibody-based ELISA), and steady-state mRNA levels of the mucin gene MUC2 were determined. ROFA was the most toxic of the dusts tested, as it significantly increased LDH release following a 24-h incubation with 50 μg/cm2 ROFA. ROFA also enhanced MUC2 mRNA after 4-h exposure, and mucin secretion after 8 h. ROFA-induced mucin secretion and cytotoxicity were attenuated by the oxidant scavenger, dimethylthiourea (DMTU). ROFA exposure also depleted cells of glutathione (GSH). Relatedly, depletion of intracellular GSH by treatment of the cells with buthionine sulfoxamine (BSO) also provoked mucin secretion, as well as enhancing the secretory effect of ROFA when the two agents were added together. L-NMA, the nitric oxide synthase (NOS) inhibitor, did not affect ROFA-induced mucin secretion. Of the soluble transition metals in ROFA (nickel, iron, vanadium), only vanadium individually, or combinations of the metals containing vanadium, provoked secretion. The results suggest ROFA enhances mucin secretion and generates toxicity in vitro to airway epithelium via a mechanism(s) involving generation of oxidant stress, perhaps related to depletion of cellular antioxidant capacity. Deleterious effects of inhalation of ROFA in the respiratory tract in vivo may relate to these cellular responses. Vanadium, a component of ROFA, may be important in generating these reactions.

TEM FIB Lift-Out of Mount Saint Helens Volcanic Ash

Focused Ion Beam (FIB) specimen preparation for both scanning and transmission electron microscopy (SEM and TEM respectively) has seen an increase in usage over the past few years. The advantage to the FIB is that site specific cross sections (or plan view sections) may be fabricated quickly and reproducibly from numerous types of materials using a finely focused beam of Ga+ ions [1,2]. It was demonstrated by Prenitzer et al. that TEM specimens may be acquired from individual Zn powder particles by employing the FIB LO specimen preparation technique [3]. In this paper, we use the FIB LO technique to prepare TEM specimens from Mount Saint Helens volcanic ash.Volcanic ash from Mount Saint Helens was obtained at the Microscopy and Microanalysis 1998 meeting in Atlanta. TEM analysis of the ash was performed using the FIB lift out technique [1]. Ash powders were dusted onto an SEM sample stud that had been coated with silver paint.