Abstract
Synthetic Aperture Radar (SAR) remote sensing plays a significant role in volcano monitoring despite the measurements’ non real-time nature. The technique’s capability of imaging the spatial extent of ground motion has especially helped to shed light on the location, shape, and dynamics of subsurface magmatic storage and transport as well as the overall state of activity of volcanoes worldwide. A variety of different deformation phenomena are observed at exceptionally active and frequently erupting volcanoes, like Piton de la Fournaise on La Réunion Island. Those offer a powerful means of investigating related geophysical source processes and offer new insights into an active volcano’s edifice architecture, stability, and eruptive behavior. Since 1998, Interferometric Synthetic Aperture Radar (InSAR) has been playing an increasingly important role in developing our present understanding of the Piton de la Fournaise volcanic system. We here collect the most significant scientific results, identify limitations, and summarize the lessons learned from exploring the rich Piton de la Fournaise SAR data archive over the past ~20 years. For instance, the technique has delivered first evidence of the previously long suspected mobility of the volcano’s unsupported eastern flank, and it is especially useful for detecting displacements related to eruptions that occur far away from the central cone, where Global Navigation Satellite System (GNSS) stations are sparse. However, superimposed deformation processes, dense vegetation along the volcano’s lower eastern flank, and turbulent atmospheric phase contributions make Piton de la Fournaise a challenging target for applying InSAR. Multitemporal InSAR approaches that have the potential to overcome some of these limitations suffer from frequent eruptions that cause the replacement of scatterers. With increasing data acquisition rates, multisensor complementarity, and advanced processing techniques that resourcefully handle large data repositories, InSAR is progressively evolving into a near-real-time, complementary, operational volcano monitoring tool. We therefore emphasize the importance of InSAR at highly active and well-monitored volcanoes such as Mount Etna, Italy, Kīlauea Volcano, Hawai’i, and Piton de la Fournaise, La Réunion.
Highlights
Magma movement through volcanic edifices is usually accompanied by measurable indicators of volcanic unrest, the most reliable of which are seismicity, gas emissions, and surface deformation.Characterizing and better understanding the subsurface processes in terms of their spatio-temporal dynamics requires natural study sites that are (a) highly active and (b) well-monitored over long time periods by a dense network of instrumentation
The first dedicated Interferometric Synthetic Aperture Radar (InSAR) study at Piton de la Fournaise was published in 1999 by Sigmundsson et al [23], who detected ground displacements associated with the 9 March 1998–21 September 1998 eruption of Piton de la Fournaise using satellite data collected by the Canadian RADARSAT-1 satellite (RSAT1)
Surface deformation measurements derived from these data using InSAR and MT-InSAR techniques complement an elaborated ground deformation monitoring network operated by OVPF-IPGP (Figures 2 and 3)
Summary
Magma movement through volcanic edifices is usually accompanied by measurable indicators of volcanic unrest, the most reliable of which are seismicity, gas emissions, and surface deformation. The volcano’s interior has been imaged down to a depth of about 10 km by means of geophysical data (Figure 1), and it can be roughly described as a pile of poorly consolidated eruption deposits that host a shallow plumbing system consisting of several intermittently connected magma reservoirs, the shallowest of which is located at ~2–2.5 km depth below the summit craters [1,16] This is the central magmatic storage from which most of the laterally propagating dikes feeding recent eruptions are initiating or passing through. During the major 30 March to 1 May 2007 distal eruption that excelled common Piton de la Fournaise eruptions by an order of magnitude in terms of lava flow volume, the Dolomieu summit crater collapsed This event destroyed the upper reservoir and distribution system and changed the eruptive behavior of the volcano. This was followed by a rest period of 41 months between 2011 and June 2014 before another phase of nearly continuous refilling and high activity began [21], which is ongoing as of 31 December 2019
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