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Margaret Mangan

Publications and source records attributed to Margaret Mangan.

3 recordsLinked to original sources
USGS2021

Constraints on deep, CO2-rich degassing at arc volcanoes from solubility experiments on hydrous basaltic andesite of Pavlof Volcano, Alaska Peninsula, at 300 to 1200 MPa

The solubility of CO 2 in hydrous basaltic andesite was examined in f O2 -controlled experiments at a temperature of 1125 °C and pressures between 310–1200 MPa. Concentrations of dissolved H 2 O and CO 2 in experimental glasses were determined by ion microprobe calibrated on a subset of run glasses analyzed by high-temperature vacuum manometry. Assuming that the solubility of H 2 O in mafic melt is relatively well known, estimates of 𝑋H2Ofluid and 𝑃H2Ofluid in the saturating fluid were modeled, and by difference, values for 𝑋CO2fluid and 𝑃CO2fluid were obtained ( X CO2 ~0.5–0.9); f CO2 could be then calculated from the fluid composition, temperature, and pressure. Dissolved H 2 O over a range of 2.3–5.5 wt% had no unequivocal influence on the dissolution of CO 2 at the pressures and fluid compositions examined. For these H 2 O concentrations, dissolved CO 2 increases with f CO2 following an empirical power-law relation: dissolved CO 2 (ppmw) = 14.9−3.5+4.5 [ f CO2 (MPa)] 0.7±0.03 . The highest-pressure results plot farthest from this equation but are within its 1 standard-error uncertainty envelope. We compare our experimental data with three recent CO 2 -H 2 O solubility models: Papale et al. (2006) ; Iacono-Marziano et al. (2012) ; and Ghiorso and Gualda (2015) . The Papale et al. (2006) and Iacono-Marizano et al. (2012) models give similar results, both over-predicting the solubility of CO 2 in a melt of the Pavlof basaltic andesite composition across the f CO2 range, whereas the Ghiorso and Gualda (2015) model under-predicts CO 2 solubility. All three solubility models would indicate a strong enhancement of CO 2 solubility with increasing dissolved H 2 O not apparent in our results. We also examine our results in the context of previous high-pressure CO 2 solubility experiments on basaltic melts. Dissolved CO 2 correlates positively with mole fraction (Na+K+Ca)/Al across a compositional spectrum of trachybasalt-alkali basalt-tholeiite-icelandite-basaltic andesite. Shortcomings of current solubility models for a widespread arc magma type indicate that our understanding of degassing in the deep crust and uppermost mantle remains semi-quantitative. Experimental studies systematically varying concentrations of melt components (Mg, Ca, Na, K, Al, Si) may be necessary to identify solubility reactions, quantify their equilibrium constants, and thereby build an accurate and generally applicable solubility model.

Alaska↗
USGS2019

California’s exposure to volcanic hazards

The potential for damaging earthquakes, landslides, floods, tsunamis, and wildfires is widely recognized in California. The same cannot be said for volcanic eruptions, despite the fact that they occur in the state about as frequently as the largest earthquakes on the San Andreas Fault. At least ten eruptions have taken place in the past 1,000 years, and future volcanic eruptions are inevitable. The U.S. Geological Survey’s (USGS) national volcanic threat assessment identifies eight young volcanic areas in California as moderate, high, or very high threat. Of the eight volcanic areas that exist in California, molten rock resides beneath at least seven of these—Medicine Lake volcano, Mount Shasta, Lassen Volcanic Center, Clear Lake volcanic field, the Long Valley volcanic region, Coso volcanic field, and Salton Buttes—and are therefore considered “active” volcanoes producing volcanic earthquakes, toxic gas emissions, hot springs, geothermal systems, and (or) ground movement. The USGS California Volcano Observatory in Menlo Park, California, monitors these potentially hazardous volcanoes to help communities and government authorities understand, prepare for, and respond to volcanic activity. Although volcanic activity can sometimes be forecast, eruptions, like earthquakes or tsunamis, cannot be prevented. Understanding the hazards and identifying what and who is in harm’s way is the first step in mitigating volcanic risk and building community resilience to volcanic hazards. This report, which was prepared in collaboration with the California Governor’s Office of Emergency Services and the California Geological Survey, provides a broad perspective on the state’s exposure to volcanic hazards by integrating volcanic hazard information with geospatial data on at-risk populations, infrastructure, and resources. This information is intended to prompt site- and sector-specific vulnerability analyses and preparation of hazard mitigation and response plans.

California↗