|Paper title||Operational use of Sentinel 1 data and interferometric methods to detect precursors for volcanic hazard warning system: the case of La Palma volcanic complex last eruption.|
|Form of presentation||Poster|
Operational use of Sentinel 1 data and interferometric methods to detect precursors for volcanic hazard warning system: the case of La Palma volcanic complex last eruption.
Ignacio Castro-Melgar1,2, Theodoros Gatsios2,4, Janire Prudencio1,3, Jesús Ibáñez1,3 and Issaak Parcharidis2
1Department of Theoretical Physics and Cosmos, University of Granada (Spain)
2Department of Geography, Harokopio University of Athens (Greece)
3Andalusian Institute of Geophysics, University of Granada (Spain)
4Department of Geophysics and Geothermy, National and Kapodistrian University of Athens (Greece)
La Palma is the youngest island of the Canary Islands (Spain) and is situated in the NW area. The Canary archipelago is a chain of seven volcanic islands in the Atlantic Ocean off the coast of Africa. This set of islands, islets and seamounts are aligned NE-SW and host a high potential risk due to their active volcanism especially in the western and youngest islands (La Palma and El Hierro). The origin of the volcanism in the Canary Archipelago started in Oligocene and continues active (Staudigel & Schmincke, 1984), the mechanism that originated its volcanism is still under debate by the scientific community. The most accepted models are the propagation fracture from the Atlas Mountains (Anguita & Hernán, 1975) or the existence of a hotspot or mantle plume (Morgan, 1983, Carracedo et al., 1998) among others models. In the last decades different volcanic manifestations occurs in the Canary archipelago such as the seismic series of Tenerife in 2004, the reactivations and eruptions of El Hierro between 2011 and 2014 and the seismic series on La Palma in 2017, 2018, 2020 and 2021.
Volcanic activity in La Palma first originated with the formation of an underwater complex of seamounts and a plutonic complex between 3 and 4 Ma . Is the most volcanic active island in the Canary archipelago in historical times, 7 eruptions have been reported (1585, 1646, 1677, 1712, 1949, 1971 and 2021) The last eruption in the volcanic complex of Cumbre Vieja, currently in progress (November, 2021), is causing serious implications for the inhabitants of the island with near 3000 buildings destroyed.
For this study we use Sentinel 1 A/B TOPSAR (C band), SLC product in both orbits (ascending and descending orbits). Synthetic Aperture Radar (SAR) is a powerful remote sensing satellite sensor used for Earth observation (Curlander & McDonough, 1991). The methodologies used are two, conventional Differential SAR Interferometry (DInSAR) and the MTInSAR of SBAS method. DInSAR allows measurements of land deformation very precisely and It has applications in the field of volcanology.
Long deformation dataset can be analysed using large stacks of SAR images in the same area using multitemporal differential SAR interferometry techniques. These techniques are based in the use of permanently coherent Persistent Scatterers (PSs) and/or temporally coherent Distributed Scatterers (DSs). In urban areas there are a prevalence of PSs allowing an individual analysis of the structures on the ground, meanwhile the DS methods have similar scattering properties and can be used together in order to analyse the deformation even in rural areas where there are low PSs density. Small Baseline Subset (SBAS) method is include in DS methods, SBAS is an of multi-temporal InSAR technique for detecting deformations with millimetre precision using a stack of SAR interferograma (Virk et al., 2018)
For DInSAR technique two different interferometric pairs have been analysed (i) 5/8/2021 and 16/09/2021 in descending orbit and (ii) 09/08/2021 and 14/09/2021 in ascending orbit. The software used for the process was SNAP 8.0 (ESA). In SBAS method two different dataset was analysed (ascending and descending orbit), (a) 24 images of relative orbit 60 Sentinel-1A/B TOPSAR (c-band) between 5 of May 2021 to 14 September 2021 and (b) 23 images of relative orbit 169 Sentinel-1A/B TOPSAR (C-band) between 1st May 2021 to 16 September 2021. The datasets were processed with GAMMA software.
3. RESULTS AND CONCLUSIONS
DInSAR images in wrapped interferograms in ascending and descending orbits show fringes in the southern part of La Palma, these patterns of the fringes are not identical between the because they cover different periods, however, the geographical location of the patterns coincide (Cumbre Vieja volcanic complex in the South of the island).
The SBAS estimated deformation velocities in ascending and descending dataset show an uplift trend up to 5 cm in the southern area, it is possible observe the deformation trend have two different stages, a first period of rest with maximum downlift and uplift of 1 cm and a second period between de last days of August until the end of the studied period (mid of September) when an abrupt uplift started with maximum deformation of 5cm.
In this study it is possible to observe that SAR interferometry (conventional and multi-temporal) allow us to know that eruption of Cumbre Vieja in La Palma was preceded by a prior deformation process that is an obvious symptom of a volcanic unrest and these techniques can be used operationally in early warning system with the aim of taking measures in order to mitigate volcanic risk.
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