More than 500 million people live close to active volcanoes. Evidence suggests that, throughout history, societies have been affected and destroyed by catastrophic eruptions. In the 1900s alone almost 100000 people were killed by volcanic explosions and their associated hazards. Explosive eruptions inject enormous columns of ash and debris into the atmosphere and discharge fast avalanches of hot gas and rocks on the slopes of volcanic edifices. Lava dome eruptions represent a style of volcanism of distinctive interest because of their potentially catastrophic effects. The hazards from this type of eruptions are well-known, due to the unpredictable transitions from slow effusion of viscous lava to violent explosive activity, and to the propensity of volcanic domes to suddenly collapse spawning devastating pyroclastic flows. Over the past few decades shifts in eruptive style were reported at several lava dome volcanoes worldwide. The underlying processes driving these transitions, however, remain poorly understood, and geophysical measurements documenting them are also very rare. The Santiaguito lava dome complex in Guatemala has been continuously erupting since 1922 and it has switched several times between effusive and explosive eruption regimes, even displaying the two types of activity simultaneously. At the time of this writing Santiaguito is undergoing a major transition from effusive to explosive behaviour marked by some the largest eruptive events ever recorded at this lava dome complex. The new activity started with a large explosion on 11 April, 2016, which produced an ash column that rose to a height in excess of 4.5 km above the vent and was clearly visible in satellite images. Preliminary estimates by local scientists suggest that this explosion was two orders of magnitude more energetic than anything recorded at Santiaguito over the past 5-6 years. The new activity offers a rare opportunity to document and investigate the geophysical fingerprint of a sudden switch in eruptive style at a lava dome volcano, and to decipher its underlying mechanisms. A geophysical deployment, including seismic, deformation and acoustic measurements is the ideal framework to seize an opportunity that is not frequently available. The proposed experiment will help addressing key scientific questions on activity at lava dome volcanoes, with impact on hazard assessment and risk mitigation in this and other eruption prone areas. The pool of target beneficiaries is broad and includes scientists within academia, civil defense authorities, policy makers and communities living nearby active volcanoes.

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.

An eruption of Fuego volcano, Guatemala, on 3rd June 2018, had tragic outcomes when an entire village was inundated by pyroclastic flows. The eruption has prompted evacuations of around 12,000 people. This event resulted in changes to hazard, exposure and vulnerability, demonstrating the complex and dynamic nature of ongoing and future risk. This proposal seeks to characterise this dynamic risk observed in the natural environment, and understand the interactions between dynamic risk and society. Following the 3rd June eruption of Fuego, evacuations have resulted in reduced exposure in some regions, however, vulnerability (physical, systemic, functional, social, economic and political) remains high and is a key component of the evolving risk. In particular, systemic and functional vulnerability are believed to be highly dynamic. This provides an opportunity to investigate how the evolving hazard situation at Fuego, combined with changes in exposure and highly dynamic systemic and functional vulnerability, play out to affect risk in a context where both recovery and continued eruption risk management are ongoing. This opportunity is urgent: we must characterise changing hazard, exposure and vulnerability through time. Although the nature of the hazard can be investigated retrospectively, documenting changes to exposure (evacuations and reoccupations) and vulnerability as they respond to changing hazard and socio-economic conditions needs to be done as it occurs. For example, it is important to document physical vulnerability on buildings already impacted by the pyroclastic flows before further damage by weather or heavy machinery occurs, or document road closures next to affected drainages which can constitute a major element of the systemic vulnerability to lahars or pyroclastic flows of a community isolated by that road closure. Information on systemic vulnerability at this level of granularity is not normally documented in Guatemala, thus will not be available for later study. Through this proposed work, we will collect an unprecedented dataset on vulnerability, documenting physical vulnerability of buildings impacted by pyroclastic flows before any further damage. When considering risk to life by volcanic flow hazards and lahars however, physical vulnerability of infrastructure can be reduced to a binary effect (impacted or not. It is actually systemic and functional vulnerability that are the more important, and harder to ascertain, unknowns. A key research component, therefore, is to test the hypothesis that for volcanic flow related hazards, in contrast to tephra hazards, it is widespread systemic vulnerability and not physical vulnerability of the footprint of potential impact that is the root cause of risk. This is important because much of the work currently undertaken on risk in volcanology is led by frameworks used for tephra fall hazards, yet flow impacts and risk are very different. The project is will-aligned with the UN Sendai Framework for Disaster Risk Reduction, as well as recent initiatives in the wider volcanology community to engage and improve our capacity to do risk well. We will use a combination of volcanology field approaches, forensic approaches, and interviews to gather the information.

This project is based on in-depth research in rural and indigenous communities in the cordillera of Guatemala (volcanic arc and southern highlands) that are located close to active volcanoes and in the vicinity of Lake Atitlán. This region has an extraordinarily high level of hazard exposure that intersects with, and is exacerbated by, existing forms of socio-economic vulnerability. People die, suffer and lose livelihoods in disasters in part because of Guatemala's geological and climatological conditions that make it prone to earthquakes, volcanic eruptions and hurricanes, as well as frequent landslides during the rainy season. The dynamic and interactive nature of these risks are still poorly understood. There is then an urgent need to gain better understandings of physical processes and, in particular, of multihazard interactions in the Guatemalan context from a scientific perspective. However, this hazard exposure cannot be separated from long histories of landlessness, state-led violence and genocide that manifest themselves today in colonial and discriminatory attitudes towards poor indigenous and mixed race (ladino) Guatemalans. Such attitudes result in failures by authorities to protect, warn, evacuate survivors, exhume and properly count the dead, and to relocate or rehouse people with dignity and in culturally appropriate ways. These experiences also mean that local people often do not trust state agencies or western science, and indigenous peoples also have their own knowledge systems and modes of understanding risk and resilience that they deem to be more reliable. The losses and complexities of recent disasters such as the June 2018 eruption of the Fuego volcano and the building of resilient communities urgently require research that brings physical sciences into dialogue not only with social sciences and humanities, but also with diverse cosmovisions and beliefs. This project involves a close collaboration between physical scientists, social scientists, humanities scholars and Guatemalan community leaders in communities exposed to multiple forms of risk. It is based on a shared commitment to reduce the suffering caused by hazards and disasters but involves people who work with very different epistemic, theoretical and methodological approaches and knowledge frameworks. We ask whether we can better understand risk and do research that is both respectful and useful to local people by putting these different knowledge systems on an equal footing. We will therefore combine quantitative monitoring techniques with artistic and ethnographic work and a range of community engagement activities. The scientific and the cultural will be combined in a 8-episode television series produced in collaboration with local organizations, actors and mediamakers in which the complexity of rural community lives and livelihoods of indigenous peoples living with risk will be ethically represented and followed up by a range of outreach activities in community spaces and on radio, television and social media. We will produce a cultural product that will provoke high levels of audience engagement and debate by scientists, community members, development practitioners, emergency managers and government agents.