Alexa R. Van Eaton

Modeling ash fall distribution from a Yellowstone supereruption

We used the volcanic ash transport and dispersion model Ash3d to estimate the distribution of ashfall that would result from a modern-day Plinian supereruption at Yellowstone volcano. The simulations required modifying Ash3d to consider growth of a continent-scale umbrella cloud and its interaction with ambient wind fields. We simulated eruptions lasting 3 days, 1 week, and 1 month, each producing 330 km3 of volcanic ash, dense-rock equivalent (DRE). Results demonstrate that radial expansion of the umbrella cloud is capable of driving ash upwind (westward) and crosswind (N-S) in excess of 1500 km, producing more-or-less radially symmetric isopachs that are only secondarily modified by ambient wind. Deposit thicknesses are decimeters to meters in the northern Rocky Mountains, centimeters to decimeters in the northern Midwest, and millimeters to centimeters on the East, West, and Gulf Coasts. Umbrella cloud growth may explain the extremely widespread dispersal of the ∼640 ka and 2.1 Ma Yellowstone tephra deposits in the eastern Pacific, northeastern California, southern California, and South Texas.

Volcanic lightning and plume behavior reveal evolving hazards during the April 2015 eruption of Calbuco Volcano, Chile

Soon after the onset of an eruption, model forecasts of ash dispersal are used to mitigate the hazards to aircraft, infrastructure, and communities downwind. However, it is a significant challenge to constrain the model inputs during an evolving eruption. Here we demonstrate that volcanic lightning may be used in tandem with satellite detection to recognize and quantify changes in eruption style and intensity. Using the eruption of Calbuco volcano in southern Chile on 22 and 23 April 2015, we investigate rates of umbrella cloud expansion from satellite observations, occurrence of lightning, and mapped characteristics of the fall deposits. Our remote sensing analysis gives a total erupted volume that is within uncertainty of the mapped volume (0.56 ± 0.28 km3 bulk). Observations and volcanic plume modeling further suggest that electrical activity was enhanced both by ice formation in the ash clouds >10 km above sea level and development of a low-level charge layer from ground-hugging currents.

High-flying diatoms: Widespread dispersal of microorganisms in an explosive volcanic eruption

Explosive eruptions create a transient bridge between the solid Earth and atmosphere, frequently injecting volcanic aerosols to stratospheric levels. Although known to disrupt terrestrial and aquatic ecosystems at the surface, the role of explosive volcanism in airborne transport of microscopic organisms has never been characterized. This study documents abundant freshwater diatoms (microskeletons of siliceous algae) in widespread tephra from the 25.4 ka Oruanui eruption of Taupo volcano, New Zealand. By matching the tephra-hosted species assemblages to those in coerupted clasts of lacustrine sediment, we demonstrate that ~0.6 km 3 of diatom remains were incorporated during magma-water interaction with a lake system overlying the vents, and were dispersed along with fi ne ash particles hundreds of kilometers downwind. One of the dominant species, Cyclostephanos novaezeelandiae, is endemic to New Zealand’s North Island and serves as a unique identifi er of the eruptive source region. Our results suggest that dispersal of microorganisms may be an overlooked feature of a number of ancient and modern eruptions, and indicate a novel pathway of microbe transport in airborne volcanic plumes. We conclude that the biogenic signatures contained within distal tephras have potential application in the characterization of eruption dynamics, location, and environmental settings of volcanic source areas.

Volcanic tremor and plume height hysteresis from Pavlof Volcano, Alaska

Hearing a volcanic plume Monitoring remote eruptions—such as that of Pavlof Volcano, Alaska, in 2016—is challenging. Fee et al. found that the height of the ash plume during the Pavlof eruption could be inferred from sound waves detected by distant infrasound arrays and measurements of seismic tremor. The use of sound waves for monitoring is uncommon but well suited for remote eruptions, especially when we lack visual or satellite observations. Science, this issue p. 45 The seismic and infrasonic volcanic tremors track ash plume height from the 2016 eruption of Pavlof Volcano. The March 2016 eruption of Pavlof Volcano, Alaska, produced an ash plume that caused the cancellation of more than 100 flights in North America. The eruption generated strong tremor that was recorded by seismic and remote low-frequency acoustic (infrasound) stations, including the EarthScope Transportable Array. The relationship between the tremor amplitudes and plume height changes considerably between the waxing and waning portions of the eruption. Similar hysteresis has been observed between seismic river noise and discharge during storms, suggesting that flow and erosional processes in both rivers and volcanoes can produce irreversible structural changes that are detectable in geophysical data. We propose that the time-varying relationship at Pavlof arose from changes in the tremor source related to volcanic vent erosion. This relationship may improve estimates of volcanic emissions and characterization of eruption size and intensity.

Phreatomagmatic and Related Eruption Styles

This chapter describes “wet” explosive eruptions, and their products, resulting from the combination of magmatic heat and “external water,” such as surface water or groundwater. Nine case studies illustrate some of the defining characteristics of wet eruptions, and how they can be recognized through direct observation and in the geological record. Water-influenced eruptions in nature occur well outside the boundaries of simplified definitions such as “phreatomagmatic,” “phreatic,” and “hydrothermal.” The case studies make it clear that we require more rigorous, comprehensive criteria to distinguish phreatomagmatic eruption styles. A second compelling need is comprehensive modeling of the thermodynamics of such eruptions.

A novel application of radionuclides for dating sediment cores from sandy, anthropogenically disturbed estuaries

Reliablesedimentationhistoriesaredifficulttoobtaininsandyoranthropogenicallyimpactedcoastalsystems with disturbed sediment profiles and low initial radionuclide activities. This study addresses the problem using radionuclides in sediment cores from Naples Bay estuary, Florida, USA. Non-steady sedimentation and nuclide scavenging processes are shown to limit application of traditional radiometric dating models in this system. Whole-core inventories of excess 210 Pb activity ( 210 Pbxs) varied from 21 to 96dpmcm � 2 among sites, and initial sediment 210 Pbxs activitieswerelow,decreasingnon-uniformlywithdepthinmostcores.Activitiesofthreeradioisotopesusedforsediment dating ( 226 Ra, 210 Pb, and 137 Cs) were compared with grain size and organic matter (OM) distributions to assess the factors that influence accumulation of radionuclides. Regression analysis indicated that radionuclide activities were more strongly correlated with OM content than with grain size parameters, and a novel OM-normalisation procedure was developed to correct for preferential nuclide associations. Normalised 210 Pbxs profiles provide evidence for shifts in sedimentation rates and episodic erosion events in regions of the estuary where anthropogenic disturbance is known to have occurred. Our results emphasise the need to consider radionuclide scavenging by OM in sandy coastal sediments when establishing sedimentation histories. Additional keywords: Cs-137, estuaries, grain size effect, organic matter, Pb-210, preferential scavenging, radioisotopes, Ra-226.

New Zealand supereruption provides time marker for the Last Glacial Maximum in Antarctica

Multiple, independent time markers are essential to correlate sediment and ice cores from the terrestrial, marine and glacial realms. These records constrain global paleoclimate reconstructions and inform future climate change scenarios. In the Northern Hemisphere, sub-visible layers of volcanic ash (cryptotephra) are valuable time markers due to their widespread dispersal and unique geochemical fingerprints. However, cryptotephra are not as widely identified in the Southern Hemisphere, leaving a gap in the climate record, particularly during the Last Glacial Maximum (LGM). Here we report the first identification of New Zealand volcanic ash in Antarctic ice. The Oruanui supereruption from Taupo volcano (25,580  ±  258 cal. a BP) provides a key time marker for the LGM in the New Zealand sector of the SW Pacific. This finding provides a high-precision chronological link to mid-latitude terrestrial and marine sites, and sheds light on the long-distance transport of tephra in the Southern Hemisphere. As occurred after identification of the Alaskan White River Ash in northern Europe, recognition of ash from the Oruanui eruption in Antarctica dramatically increases the reach and value of tephrochronology, providing links among climate records in widely different geographic areas and depositional environments.