High Resolution Radar Imaging of Pyroclastic Density Currents

Pyroclastic density currents (PDCs) are clouds of ash and rock, generated during eruptions, which propagate down volcanoes at high speed. They are the major hazard at many active volcanoes and have killed thousands of people. Our current ability to predict their behaviour and plan for their effects is limited, in part, by our incomplete knowledge of their flow dynamics. The proposed research will revolutionise our understanding of PDCs by obtaining, for the first time ever, measurements of position in time, hence velocity, of the dense core of moving PDCs using an advanced custom-built radar system (GEODAR). GEODAR has been developed and successfully used on snow avalanches, dramatically improving our knowledge of their dynamics. The project will build and deploy three GEODAR systems that have a spatial range resolution of 0.375 m and will image the dense core flow at 100 Hz: a spatial and time resolution never achieved before in studies of PDCs. GEODAR will easily penetrate the ash cloud to image the dense, destructive underflow, and can observe all particles larger than 30 mm. This novel system will be able to track PDCs along their flow paths and will allow us to image internal surges, roll-waves and flow fronts and reconstruct the velocity structure of moving PDCs. This data will enable the rigorous testing of PDC flow models and provide fundamental insights into their flow so that improved models can be developed.

In addition, the flow path and deposits of the PDCs will be digitally mapped by a drone at 30 mm resolution in order to resolve the lateral extent and location of the flow. Features in the digital terrain maps will be directly matched with the features observed in the radar data and this will greatly add to the understanding of PDC emplacement mechanisms. For some flows we expect to have high resolution DTMs both before and after the event, and we will produce erosion and deposition maps. This data feeds in to the final part of the project which is the computer simulation of PDCs. The simulation code produces will be useful for predicting the path and forces of PDCs which is necessary for saving lives and protecting infrastructure. The code will be made freely available and a workshop run on its use. The DTM will be used for running the SHALTOP code and the results will be compared with GEODAR data and the erosion and deposition maps. SHALTOP is a simulation code developed, over the past fifteen years, by a French team partner in this project. It can be run with a variety of flow laws and we will determine which flow law best matches the data and from there we develop improvements. Such a detailed comparison has never been done before due to the lack of data from flowing PDCs. We have chosen Santiaguito volcano, Guatemala, as the test site. It is one of the world's most active volcanoes, which has been erupting since 1922 and dozens of PDCs are generated every year. The team has extensive experience working at this site and the local volcano observatory is an enthusiastic participant in the project. In addition, the terrain around the volcano is ideally suited for the location of GEODAR, with nearly complete sight-lines to the likely flow paths. The systems will be remotely triggered using a combination of infrasound and seismic signals. The three GEODAR systems will be stand- alone solar-powered units and communicate via a satellite-phone data link. The data storage will be on SSDs mounted in fireproof crash boxes so that they can withstand inundation.

This research will produce the first ever high resolution position, and hence velocity, data for the dense core of flowing PDCs and the first ever model comparison with such data. The project will develop improved theoretical and computational models for PDCs and improve the accuracy of hazard assessments around volcanoes. The ultimate aim is to improve physical knowledge of these destructive natural hazards with the potential to save hundreds of lives.

This project will provide the first ever high resolution measurements
of position in time, hence velocity, of the dense core of moving
pyroclastic density currents (PDCs). This data will improve our
understanding of the dynamics regulating the propagation of PDCs which
is fundamental for generating more accurate theoretical and
computational models which are widely used in hazard assessments
around PDC-prone volcanoes.

Major beneficiaries beyond include government and non-governmental
organisations involved in civil protection planning and preparation at
active volcanoes. These include national geological surveys (e.g.,
BGS, USGS), volcano observatories and regional and national civil
protection departments charged with policy-making during
emergencies. Primary amongst these is the one of our project partners, the Instituto
Nacional de Sismologia, Volcanologia, Meteorologia e Hidrologia,
Guatemala, who monitor Santiaguito volcano. This and other, similar, organisations would
benefit from an improved knowledge about PDCs that will be translated
into improved theoretical and computational models of PDCs. This will
lead to improved and more accurate assessments of the inundation zones
and runout distances of PDCs. This benefit will become apparent
towards the end of the proposed research once the data has been
processed and analysed, and once models have been tested and new
models developed. Dissemination of this information will be initially
through www.vhub.org - an online platform for the volcano science
community that allows numerical codes to be run remotely. We will also
organize a workshop at the end of the grant for invited modellers and
practitioners to provide hands-on instruction in the use of the data
and code.

This research has much potential to capture the public's imagination,
due to the visceral, news-worthy nature of PDCs and natural hazards in
general. In particular, the recent eruption of Fuego volcano,
Guatemala's most severe volcanic eruption in 45 years which affected 1.7
million people with a death toll of around 200 people, has raised public
awareness of the importance of managing volcanic hazards and improving
risk assessments. We will aim to engage the public through a number of
platforms from the very start of the proposed research including
regular tweets and a website. We envisage that the general public will
benefit from (1) an improved understanding and appreciation of the
nature of PDCs and the hazards associated with them; (2) exposure to
the science behind volcanic eruptions and their products; and (3) from
engagement with science, and with physics and earth sciences in
particular.