Surveying Volcanic Arcs with Satellite Radar Interferometry: The Central Andes, Kamchatka, and Beyond

Satellite Interferometric Synthetic Aperture Radar (InSAR) permits both synoptic and detailed surveys of mag-matic activity in volcanic arcs. To illustrate this capability, we summarize here the results of an extended study of inferred magmatic activity in the central Figure 1. Interferometric coherence (a measure of the quality of the Interferometric Synthetic Aperture Radar, or InSAR, measurement) from ERS-1 and-2 (5.7 cm wavelength) draped over shaded relief for the Andes. (A) Reference map, with the green box showing the area in B and the red box indicating the area in C. Black lines show international borders. (B) The central Andes. Triangles are Holocene volcanoes (Smithsonian Institution, 2004). Even though measurements are taken during different seasons and span several years, coherence is high across the region (for a list of dates and data used, see Pritchard and Simons, 2004). We observe the highest interferometric coherence near the arid coast. (C) Coherence in the southern Andes taken during the austral summer and spanning only a few years. Coherence is regionally low, but high in rocky areas (like the Taitao Peninsula). Coherence is maintained on many lava flows (not resolved at the scale of this image), so that deformation measurements are still possible near many volcanoes. Usable data are only available in the southern portion of the southern arc. 2004), as well as new results from Kamchatka. In the central Andes, encompassing parts of Peru, Bolivia, Chile, and Argentina, we have observed ~900 volcanoes between 1992 and 2003 and found four previously undocumented sources of deformation. Coupled with surveys in other arcs, this deformation indicates that short-lived pulses of magma movement are common, although the relation of these movements to eruptive activity is unclear. In fact, no co-eruptive deformation was detected from eruptions at four other Andean volcanoes. In Kamchatka, the limits of current InSAR satellites are apparent in terms of the quality of the measurements and coverage of the arc. Nonetheless, we observe subsidence associated with a large lava flow that erupted 28 years ago and inflation of a geothermally active caldera. While a global inventory of volcanic arcs is impossible with current datasets, InSAR is a critical tool for understanding volcanic hazard at most of the world's poorly monitored subaerial volcanoes as well as for searching for large magma reservoirs.