Volcanic flank collapse: diversity of behaviour, hazard generation and controls on volcano evolution

The collapse of volcanoes, resulting from instability, can lead to extremely large landslides. These form avalanches of rock that may travel outwards for tens of kilometres. The impacts of such events can be devastating, destroying all in their path. Such debris avalanches have occurred many times in the past. Field evidence indicates the presence of their deposits around volcanoes worldwide. In some cases, these large landslides may be accompanied by eruption, but at other times, they may occur without a clear link to volcanic activity. Thus, there are different types of edifice collapse that may generate debris avalanches. In addition to generating debris avalanches, the collapse of a portion of a volcano can lead to changes in the subsequent activity of the volcano itself. This change in eruptive behaviour results means that the types of hazard posed by a particular volcanic system may switch through time, as part of a cycle of volcano construction and destruction. Volcanic hazards, related both to landslides and eruption, are at present unpredictable. Only by understanding in more detail the causes of failure, and how failure relates to the hazardous potential of these large landslides, can our forecasting capacity be improved. This project aims to improve our overall understanding of how volcanic debris avalanches are generated, and how different causes or types of collapse result in a range of hazards posed by avalanches. These hazards can be assessed in terms of the timing, style and size of events. The project also aims to place the collapse of volcanoes within the process of volcano formation and destruction. This can be done through understanding how collapse affects magma stored beneath the volcano, and thereby influences later volcanic activity and development. These relationships are fundamental to understanding volcanism. The approach this project will take is to incorporate existing data, from numerous detailed studies of individual volcanoes, with new data from well-known debris avalanche deposits and volcano collapses. I will assess these data for general relationships and patterns relating to the causes of collapse and avalanche processes. The selected field sites are in Mexico and Chile, where several examples of volcanic collapses are well exposed. By taking field-based and chemical measurements, debris avalanches can be placed in a time-context with activity at the collapsed volcano. Additionally, chemical data can be used to understand how magma beneath the volcano has changed through time, in terms of its storage conditions, mixing and ascent. Such data therefore provide information relating to the evolution of volcanoes through time, and how this evolution is impacted by collapse. The field and laboratory results will be strengthened by the application of calculations and models that show how collapse alters the stress and pressure conditions beneath volcanoes. Hence, changes in volcano evolution can be interpreted in light of quantitative data, and relationships between sizes and types of collapse and changes in volcanic behaviour can be better understood. This approach is important for understanding the potential types and impacts of volcanic hazards at individual volcanoes, and how these may differ through time. Further developments of this work will be to apply these finding to understand the behaviour of debris avalanches and their associated hazards in different environments. Such hazards may include changes in debris avalanche flow behaviour, or tsunami generation when debris avalanches interact with water.