Abstract
Ground-Based Interferometric Synthetic Aperture Radar (GBInSAR) is an efficient technique for capturing short, subtle episodes of conduit pressurization in open vent volcanoes like Stromboli (Italy), because it can detect very shallow magma storage, which is difficult to identify using other methods. This technique allows the user to choose the optimal radar location for measuring the most significant deformation signal, provides an exceptional geometrical resolution, and allows for continuous monitoring of the deformation. Here, we present and model ground displacements collected at Stromboli by GBInSAR from January 2010 to August 2014. During this period, the volcano experienced several episodes of intense volcanic activity, culminated in the effusive flank eruption of August 2014. Modelling of the deformation allowed us to estimate a source depth of 482 ± 46 m a.s.l. The cumulative volume change was 4.7 ± 2.6 × 105 m3. The strain energy of the source was evaluated 3–5 times higher than the surface energy needed to open the 6–7 August eruptive fissure. The analysis proposed here can help forecast shifts in the eruptive style and especially the onset of flank eruptions at Stromboli and at similar volcanic systems (e.g. Etna, Piton de La Fournaise, Kilauea).
Highlights
Ground-Based Interferometric Synthetic Aperture Radar (GBInSAR) system offers an opportunity to image deformation due to shallow dike intrusions, shallow magma movement, opening/closing of eruptive fissures/ephemeral vents as well as landslides[1,2,3,4,5,6] Since GBInSAR allows the user to choose the optimal radar location in terms of distance and incidence and azimuth angles, the deformation can be measured with exceptional geometrical resolution, while the very high sampling rate allows for continuous monitoring of the deformation[1,6,7]
The GBInSAR system consists of a transmitting and a receiving antenna moving along a rail (3 m long in the configuration deployed at Stromboli)[1]
Modelling of the deformation confirmed the presence of a very shallow reservoir consistent with the persistency of magma within Stromboli’s conduits, whose existence has been proposed before from the analysis of geochemical data[33,34], that broadly corresponds with the source location of syn-explosive deformation (350–600 m a.s.l.)[35]
Summary
The NE portion of the summit area of Stromboli has been continuously monitored since January 20036 by a GBInSAR system located on a stable section of the flank, about 1.5 km away from the crater terrace (Fig. 1). GBInSAR measures ground displacement along the LOS by computing, via cross correlation, the phase differences between the backscattered signals associated with two consecutive synthetic aperture radar (SAR) images. Due to the short time (11 min) between two subsequent measurements, interferometric displacements are usually smaller than half wavelength, and phase unwrapping procedures[21] are not necessary. Both the range and cross-range resolutions are on average 2 m × 2 m, with a precision in displacement measurements of less than 1 mm[3].
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