Contribution of fine ash to the atmosphere from plumes associated with pyroclastic density currents

A co-pyroclastic density current (co-PDC) plume forms as a mixture of fine-grained (<90 μm) particles and hot gas lofts from the top of a pyroclastic density current. Such plumes can rise tens of kilometers and inject substantial volumes of fine ash into the atmosphere with significant implications for airspace disruption, populations, livestock, and agriculture in downwind areas. Co-PDC deposits have a remarkably consistent grain size that remains constant with distance from source, regardless of eruption style, highlighting the complex sedimentation mechanisms that control deposition of co-PDC ash due to its fine grain size. Observations and numerical simulations of co-PDC onset emphasize the role played by the dynamics of PDCs in the development of co-PDC columns and plumes. The key differences between co-PDC and vent-derived plume source conditions and dispersion dynamics have important implications for application of remote sensing and numerical modeling methods

Uncertainty quantification and sensitivity analysis of volcanic columns models: results from the integral model PLUME-MoM

The behavior of plumes associated with explosive volcanic eruptions is complex and dependent on eruptive source parameters (e.g. exit velocity, gas fraction, temperature and grain-size distribution). It is also well known that the atmospheric environment interacts with volcanic plumes produced by explosive eruptions in a number of ways. The wind field can bend the plume but also affect atmospheric air entrainment into the column, enhancing its buoyancy and in some cases, preventing column collapse. In recent years, several numerical simulation tools and observational systems have investigated the action of eruption parameters and wind field on volcanic column height and column trajectory, revealing an important influence of these variables on plume behavior. In this study, we assess these dependencies using the integral model PLUME-MoM, whereby the continuous polydispersity of pyroclastic particles is described using a quadrature-based moment method, an innovative approach in volcanology well-suited for the description of the multiphase nature of magmatic mixtures. Application of formalized uncertainty quantification and sensitivity analysis techniques enables statistical exploration of the model, providing information on the extent to which uncertainty in the input or model parameters propagates to model output uncertainty. In particular, in the framework of the IAVCEI Commission on tephra hazard modeling inter-comparison study, PLUME-MoM is used to investigate the parameters exerting a major control on plume height, applying it to a weak plume scenario based on 26 January 2011 Shinmoe-dake eruptive conditions and a strong plume scenario based on the climatic phase of the 15 June 1991 Pinatubo eruption

Using the 'myVolcano' mobile phone app for citizen science in St. Vincent and the Grenadines : a pilot study

The British Geological Survey (BGS) has been working with Caribbean partners on the role of citizen science in increasing resilience to natural hazards. The work has largely focused on the potential use of the myVolcano smartphone app, which was developed by the BGS following the 2010 Eyafjallajökull and 2011 Grímsvötn eruptions in Iceland. During these eruptions the BGS asked the UK public to collect particle samples, subsequently analysing these for ash presence to map the distribution of ash fallout across the UK. These requests led to the development of the myVolcano app, which was designed to capture transboundary and distal observations of volcanic ash and emissions. The observations are made visible to other users via an interactive map built into the app. The map interface has global coverage and the data collection methods (free-text descriptions and photographs) are such that information about any natural hazard, anywhere in the world, can be captured. In 2015, BGS carried out an ESRC-DfID-NERC funded scoping study in collaboration with the University of the West Indies’ Seismic Research Centre (UWI SRC), to test the potential use of the app in environments affected by proximal volcanic hazards. The study focused on St. Vincent and the Grenadines and investigated the potential for capturing a wider variety of observations for use by the public, operational scientists and civil protection. The study, which included a combination of desk study and remote interviews, highlighted the potential for, and challenges of, using such an app for increasing resilience to natural hazards and the need for a follow-up study in St Vincent. In March 2017, a workshop and school activities were held in St. Vincent to collect feedback from potential users of myVolcano, hereafter referred to as the pilot study. Workshop participants came from across government, monitoring agencies, emergency response and telecommunications. As part of the workshop, a multi-hazard scenario was ‘played out’ to stimulate discussions on the usability of the app, data gathering and processing, and participants’ use of existing citizen science applications. Discussions developed around data validation and quality assurance, data sharing and presentation, local management of data by nominated scientists (e.g. to facilitate real-time decision making) and the associated need for a locally appropriate app (i.e. no one size fits all). This last point is particularly significant when considering the utility of an app in several countries – the user interface, at least, requires specific tailoring to the country’s needs. Using this feedback, the BGS Official Development Assistance (ODA) programme is currently funding collaborations with Caribbean partners in order to modify the app to meet the local requirements, including widening the multi-hazard application and enhancing two-way information sharing. Of particular importance is how best to share critical information with those making observations and how to make observations available to decision-makers and monitoring scientists in real-time (e.g. through local management of the app)

How does tephra deposit thickness change over time? A calibration exercise based on the 1980 Mount St Helens tephra deposit

Tephra layers are frequently used to reconstruct past volcanic activity. Inferences made from tephra layers rely on the assumption that the preserved tephra layer is representative of the initial deposit. However, a great deal can happen to tephra after it is deposited; thus, tephra layer taphonomy is a crucial but poorly understood process. The overall goal of this research was to gain greater insight into the taphonomy of terrestrial tephra layers. We approached this by a) conducting a new survey of the tephra layer from the recent, well-studied eruption of Mount St Helens on May 18th, 1980 (MSH1980); b) modelling the tephra layer thickness using an objective mathematical technique and c) comparing our results with an equivalent model based on measurements taken immediately after the eruption. In this way, we aimed to quantify any losses and transformations that have occurred. During our study, we collected measurements of tephra layer thickness from 86 locations ranging from 600 km from the vent. Geochemical analysis was used to verify the identity of tephra of uncertain origin. Our results indicated that the extant tephra layer at undisturbed sites was representative of the original deposit: overall, preservation in these locations (in terms of thickness, stratigraphy and geochemistry) had been remarkably good. However, isopach maps generated from our measurements diverged from isopachs derived from the original survey data. Furthermore, our estimate of the quantity of tephra produced during eruption greatly exceeded previous estimates of the fallout volume. In this case, inaccuracies in the modelled fallout arose from issues of sampling strategy, rather than taphonomy. Our results demonstrate the sensitivity of volcanological reconstructions to measurement location, and the great importance of reliably measured low/zero values in reconstructing tephra deposits

Increased rates of large-magnitude explosive eruptions in Japan in the late Neogene and Quaternary

Tephra layers in marine sediment cores from scientific ocean drilling largely record high-magnitude silicic explosive eruptions in the Japan arc for up to the last 20 million years. Analysis of the thickness variation with distance of 180 tephra layers from a global dataset suggests that the majority of the visible tephra layers used in this study are the products of caldera-forming eruptions with magnitude (M) &gt;6, considering their distances at the respective drilling sites to their likely volcanic sources. Frequency of visible tephra layers in cores indicates a marked increase in rates of large magnitude explosive eruptions at ~8 Ma, 6–4 Ma and further increase after ~2 Ma. These changes are attributed to major changes in tectonic plate interactions. Lower rates of large magnitude explosive volcanism in the Miocene are related to a strike-slip dominated boundary (and temporary cessation or deceleration of subduction) between the Philippine Sea Plate and southwest Japan, combined with the possibility that much of the arc in northern Japan was submerged beneath sea level partly due to previous tectonic extension of Northern Honshu related to formation of the Sea of Japan. Changes in plate motions and subduction dynamics during the ~8 Ma to present period led to (1) increased arc-normal subduction in southwest Japan (and resumption of arc volcanism) and (2) shift from extension to compression of the upper plate in northeast Japan, leading to uplift, crustal thickening and favourable conditions for accumulation of the large volumes of silicic magma needed for explosive caldera-forming eruptions

Near-real-time volcanic cloud monitoring: insights into global explosive volcanic eruptive activity through analysis of Volcanic Ash Advisories

Understanding the location, intensity, and likely duration of volcanic hazards is key to reducing risk from volcanic eruptions. Here, we use a novel near-real-time dataset comprising Volcanic Ash Advisories (VAAs) issued over 10 years to investigate global rates and durations of explosive volcanic activity. The VAAs were collected from the nine Volcanic Ash Advisory Centres (VAACs) worldwide. Information extracted allowed analysis of the frequency and type of explosive behaviour, including analysis of key eruption source parameters (ESPs) such as volcanic cloud height and duration. The results reflect changes in the VAA reporting process, data sources, and volcanic activity through time. The data show an increase in the number of VAAs issued since 2015 that cannot be directly correlated to an increase in volcanic activity. Instead, many represent increased observations, including improved capability to detect low- to mid-level volcanic clouds (FL101–FL200, 3–6 km asl), by higher temporal, spatial, and spectral resolution satellite sensors. Comparison of ESP data extracted from the VAAs with the Mastin et al. (J Volcanol Geotherm Res 186:10–21, 2009a) database shows that traditional assumptions used in the classification of volcanoes could be much simplified for operational use. The analysis highlights the VAA data as an exceptional resource documenting global volcanic activity on timescales that complement more widely used eruption datasets

Submarine landslide megablocks show half of Anak Krakatau island failed on December 22nd, 2018

As demonstrated at Anak Krakatau on December 22nd, 2018, tsunamis generated by volcanic flank collapse are incompletely understood and can be devastating. Here, we present the first high-resolution characterisation of both subaerial and submarine components of the collapse. Combined Synthetic Aperture Radar data and aerial photographs reveal an extensive subaerial failure that bounds pre-event deformation and volcanic products. To the southwest of the volcano, bathymetric and seismic reflection data reveal a blocky landslide deposit (0.214 ± 0.036 km3) emplaced over 1.5 km into the adjacent basin. Our findings are consistent with en-masse lateral collapse with a volume ≥0.175 km3, resolving several ambiguities in previous reconstructions. Post-collapse eruptions produced an additional ~0.3 km3 of tephra, burying the scar and landslide deposit. The event provides a model for lateral collapse scenarios at other arc-volcanic islands showing that rapid island growth can lead to large-scale failure and that even faster rebuilding can obscure pre-existing collapse