An official website of the United States government
We sought to develop a longer and more robust history of pollution in the Hudson River by studying LWB1-8, a high sedimentation rate core (~1 cm/yr) retrieved near Yonkers, NY. The sediment has been affected both by industrial pollution and natural disasters such as distant volcanic eruptions. In order to study this core, we analyzed its elemental composition in a variety of ways. Previous data from ITRAX scanning of the core years ago was lined up with new elemental analyses done with an XRF machine in order to pick which layers may be the most likely to contain volcanic ash. If ash particles were deemed likely in these layers, samples were run through a Franz, or magnetic materials were separated out using a Nb magnet. Then, particles of potential ash were picked out by hand. These ash candidates were then run through an SEM machine to provide a more in-depth elemental analysis of the particles as well as obtain high-resolution photos of them. Peaks in uncalibrated Ni, Ti, and SI (peaks in counts) from the ITRAK can be used to locate the depths of prospective volcanic ash layers. Ni peaks were especially good at identifying which layers may contain volcanic ash. .We found at least four layers containing volcanic ash , but there is still uncertainty about their source volcanoes. Many of the volcanic ash particles have very high Fe and very low K contents. These likely come from explosive Icelandic eruptions like those of Hekla. Other ashes have very low Fe, higher K and higher Si. These ashes likely come from volcanic arcs located at high latitudes, such as the Cascade and Aleutian arcs. This experiment has shown that it is possible to find volcanic ash in Hudson River cores. However, the number of ash particles we have retrieved so far is very small, from one to nine per age horizon. We do best at finding ash below 100 cm, where there is little industrial pollution. In future, we need to refine our methods of segregating ash from industrial debris. We must also analyze our ash particles on a microprobe and an ICPMS to determine their source volcanoes. Only then can we convert our measurements of metals versus depth into a pollution history.
more »
« less
Microphysical Effects of Water Content and Temperature on the Triboelectrification of Volcanic Ash on Long Time Scales
Abstract The effects of water and temperature on the triboelectrification of granular materials have been reported by numerous authors, but have not been studied robustly in the context of volcanic plumes. Here, we present the results of a set of experiments designed to elucidate how environmental conditions modulate the triboelectric characteristics of volcanic ash in the upper region of the convective column. We find that small amounts of water can reduce the charge collected by submillimeter‐sized ash grains by up to an order of magnitude. Increasing temperature at a constant relative humidity also appears to decrease the amount of charge gained by particles. Analysis of our data shows that if particles undergo low‐energy, low‐frequency collisions in humid environments under minute‐long time scales, charge dissipation dominates over charge accumulation. Thus, our work suggests that triboelectric charging may be an inefficient electrification mechanism outside of the gas‐thrust region where collision energies and rates are high and residence times are low.
more »
« less
- Award ID(s):
- 1645057
- PAR ID:
- 10447996
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 125
- Issue:
- 14
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Over the last decades, remote observation tools and models have been developed to improve the forecasting of ash‐rich volcanic plumes. One challenge in these forecasts is knowing the properties at the vent, including the mass eruption rate and grain size distribution (GSD). Volcanic lightning is a common feature of explosive eruptions with high mass eruption rates of fine particles. The GSD is expected to play a major role in generating lightning in the gas thrust region via triboelectrification. Here, we experimentally investigate the electrical discharges of volcanic ash as a function of varying GSD. We employ two natural materials, a phonolitic pumice and a tholeiitic basalt (TB), and one synthetic material (soda‐lime glass beads [GB]). For each of the three materials, coarse and fine grain size fractions with known GSDs are mixed, and the particle mixture is subjected to rapid decompression. The experiments are observed using a high‐speed camera to track particle‐gas dispersion dynamics during the experiments. A Faraday cage is used to count the number and measure the magnitude of electrical discharge events. Although quite different in chemical composition, TB and GB show similar vent dynamics and lightning properties. The phonolitic pumice displays significantly different ejection dynamics and a significant reduction in lightning generation. We conclude that particle‐gas coupling during an eruption, which in turn depends on the GSD and bulk density, plays a major role in defining the generation of lightning. The presence of fines, a broad GSD, and dense particles all promote lightning.more » « less
-
Abstract Magma‐water interaction can dramatically influence the explosivity of volcanic eruptions. However, syn‐ and post‐eruptive diffusion of external (non‐magmatic) water into volcanic glass remains poorly constrained and may bias interpretation of water in juvenile products. Hydrogen isotopes in ash from the 2009 eruption of Redoubt Volcano, Alaska, record syn‐eruptive hydration by vaporized glacial meltwater. Both ash aggregation and hydration occurred in the wettest regions of the plume, which resulted in the removal and deposition of the most hydrated ash in proximal areas <50 km from the vent. Diffusion models show that the high temperatures of pyroclast‐water interactions (>400°C) are more important than the cooling rate in facilitating hydration. These observations suggest that syn‐eruptive glass hydration occurred where meltwater was entrained at high temperature, in the plume margins near the vent. Ash in the drier plume interior remained insulated from entrained meltwater until it cooled sufficiently to avoid significant hydration.more » « less
-
Abstract During explosive volcanic eruptions, volcanic ash is ejected into the atmosphere, impacting aircraft safety and downwind communities. These volcanic clouds tend to be dominated by fine ash (<63 μm in diameter), permitting transport over hundreds to thousands of kilometers. However, field observations show that much of this fine ash aggregates into clusters or pellets with faster settling velocities than individual particles. Models of ash transport and deposition require an understanding of aggregation processes, which depend on factors like moisture content and local particle collision rates. In this study, we develop a Plume Model for Aggregate Prediction, a one‐dimensional (1D) volcanic plume model that predicts the plume rise height, concentration of water phases, and size distribution of resulting ash aggregates from a set of eruption source parameters. The plume model uses a control volume approach to solve mass, momentum, and energy equations along the direction of the plume axis. The aggregation equation is solved using a fixed pivot technique and incorporates a sticking efficiency model developed from analog laboratory experiments of particle aggregation within a novel turbulence tower. When applied to the 2009 eruption of Redoubt Volcano, Alaska, the 1D model predicts that the majority of the plume is over‐saturated with water, leading to a high rate of aggregation. Although the mean grain size of the computed Redoubt aggregates is larger than the measured deposits, with a peak at 1 mm rather than 500 μm, the present results provide a quantitative estimate for the magnitude of aggregation in an eruption.more » « less
-
Abstract. Volcanic fallout in polar ice sheets provides important opportunities to date and correlate ice-core records as well as to investigate theenvironmental impacts of eruptions. Only the geochemical characterization of volcanic ash (tephra) embedded in the ice strata can confirm the sourceof the eruption, however, and is a requisite if historical eruption ages are to be used as valid chronological checks on annual ice layercounting. Here we report the investigation of ash particles in a Greenland ice core that are associated with a volcanic sulfuric acid layer previouslyattributed to the 79 CE eruption of Vesuvius. Major and trace element composition of the particles indicates that the tephra does not derive fromVesuvius but most likely originates from an unidentified eruption in the Aleutian arc. Using ash dispersal modeling, we find that only an eruptionlarge enough to include stratospheric injection is likely to account for the sizable (24–85 µm) ash particles observed in the Greenlandice at this time. Despite its likely explosivity, this event does not appear to have triggered significant climate perturbations, unlike some otherlarge extratropical eruptions. In light of a recent re-evaluation of the Greenland ice-core chronologies, our findings further challenge the previousassignation of this volcanic event to 79 CE. We highlight the need for the revised Common Era ice-core chronology to be formally accepted by the widerice-core and climate modeling communities in order to ensure robust age linkages to precisely dated historical and paleoclimate proxy records.more » « less
