High resolution geodesy for active, deforming volcanoes

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Some volcanic eruptions have enormous economic and humanitarian costs, but measurements that help anticipate them can reduce their impact. The pathway of the magma to the surface is impossible to observe directly and we must rely on secondary signs such as small earthquakes, gas emission and surface deformation to infer magma movement Our proposed work uses the latter. Specifically, we will use the satellite radar interferometry technique known as InSAR to detect changes of less than 1 cm in the position of the earth's surface. InSAR can measure the pressurisation of magma reservoirs, which typically deforms the ground surface over distances of tens of kilometres and lasts for several years. Yet, it is becoming increasingly clear that there are other signals on volcanoes that are smaller in scale and occur more rapidly for which the current use of InSAR is poorly suited. We plan to observe these signals using the satellite TerraSAR-X, which operates at a shorter wavelength than its predecessors, producing images with 2 m resolution every 11 days. We have chosen to target a range of actively erupting volcanoes in Latin America, whose proximity to major population centres and infrastructure are a particular cause for concern. Radar measurements are especially important in this region since frequent cloud cover can make direct and airborne observations difficult. We will address scientific questions related to the growth of volcanic domes, major instabilities on the flank of the volcanoes and the patterns of surface deformation that accompany eruptive crises. Some volcanoes erupt almost continuously, but with especially dangerous eruptive crises occurring every year or two. At these volcanoes, we will use the frequent TerraSAR-X imagery to learn whether uplift and subsidence occur 1) during the heightened period of earthquakes and explosion lasting several months before a major eruption; 2) rapidly during the eruption itself or 3) more slowly as the volcano relaxes into a quiet period following the eruption. Other volcanoes are forming new lava domes from slow-moving, viscous magma. When new material is added particularly quickly, the dome is very unstable and collapses are accompanied by dangerous flows and ash columns. Subtle features in the high resolution radar images will give us clues as to the state of the dome, its growth rate and collapse events. Finally, low resolution images have shown that the flank of Volcan Arenal in Costa Rica is sliding rapidly downhill as new lava flows and ash falls accumulate - a sudden failure could cause a massive landslide and possibly even trigger a major explosive eruption. The new, higher resolution images will tell us if the volcano flank is moving as a single coherent block, or is actually broken up into a number of smaller blocks moving at different rates. We will work closely with the volcano observatories responsible for monitoring these volcanoes to maximize the practical utility of our work.