Dynamics of unrest before eruption at large volcanic calderas

Eruptions from large volcanic calderas have the potential to cause global disruption, but recognising characteristic warning signs remains uncertain. Common pre-eruptive patterns of local earthquakes and ground movement mimic those seen at smaller stratovolcanoes, but over several decades rather than years or less. The similarity is remarkable given the obvious differences in structure between the edifices formed by stratovolcanoes and the giant depressions, tens of kilometres across, that define calderas. It suggests that the fundamental processes driving precursory behaviour are similar independent of scale and so can also be investigated by rock-physics experiments in the laboratory.

Precursory seismicity records the sliding of faults beneath a volcano. Eruptions, however, occur when fractures open to allow magma to reach the surface. Outstanding goals are to understand how rates and locations of fault sliding can be used to trace the growth of tensile fractures. The fracturing may be driven by magma pressure or tectonic stress. This project will investigate the growth of fracture systems by integrating laboratory experiments with numerical fracture models at the temperatures, pressures and pore-fluid pressures expected beneath calderas. The results will be used to develop methods (1) to follow the evolution of crustal fractures, (2) to distinguish between magma-driven and tectonically driven fracture, and (3) to reduce uncertainty in eruption forecasts. Samples for experiments and field data for validating results will be obtained from calderas in recent unrest, and potential locations for fieldwork include Laguna del Maule in Chile, Campi Flegrei in Italy, and Bardarbunga in Iceland.