&#160;Dike intrusion before the 2021 La Palma eruption&#160;
Authors: Domínguez Cerdeña Itahiza Francisco , García Cañada Laura , Fernández García Anselmo , del Fresno Carmen , Díaz Suárez Eduardo Andrés 
Published: March 2022

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&lt;p&gt;&lt;span&gt;On 19 September 2021 at 14:10h (UTC) a volcanic eruption started&amp;#160;in the&amp;#160;South of&amp;#160;La Palma&amp;#160;(Canary Islands).&amp;#160;Just a&amp;#160;week&amp;#160;earlier,&amp;#160;on 11 September,&amp;#160;an intense seismic swarm&amp;#160;had begun&amp;#160;in the area, with the hypocenters&amp;#160;located at&amp;#160;11&amp;#160;km depth in the first days but&amp;#160;gradually approaching the surface&amp;#160;throughout the week. This activity, together with an evident&amp;#160;deformation recorded both at the island's GNSS stations and in&amp;#160;InSAR&amp;#160;measurements,&amp;#160;were&amp;#160;key to the monitoring of the reactivation&amp;#160;and estimate the&amp;#160;eruption&amp;#160;onset&amp;#160;parameters.&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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&lt;p&gt;&lt;span&gt;In this presentation we&amp;#160;show&amp;#160;the results obtained using the&amp;#160;volcanic monitoring&amp;#160;network&amp;#160;of the&amp;#160;Instituto&amp;#160;Geogr&amp;#225;fico&amp;#160;Nacional&amp;#160;(IGN)&amp;#160;before La Palma eruption.&amp;#160;Consistent results&amp;#160;have been obtained&amp;#160;combining&amp;#160;seismic and geodetic&amp;#160;techniques.&amp;#160;We have used&amp;#160;hypoDD&amp;#160;relative location algorithm to improve the hypocenters of 1323&amp;#160;earthquakes&amp;#160;of the IGN catalog.&amp;#160;Deformation results have been obtained using&amp;#160;Sentinel-1&amp;#160;images&amp;#160;to&amp;#160;get the&amp;#160;InSAR&amp;#160;interferograms&amp;#160;and&amp;#160;GNSS&amp;#160;time series&amp;#160;have been&amp;#160;computed&amp;#160;using double&amp;#160;differences&amp;#160;with Bernese software considering a regional network.&amp;#160;&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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&lt;p&gt;&lt;span&gt;At the beginning,&amp;#160;seismicity was 11 kilometers below the central part of Cumbre Vieja&amp;#160;and for&amp;#160;~6&amp;#160;days&amp;#160;it&amp;#160;migrated&amp;#160;towards the&amp;#160;surface&amp;#160;in northwest direction.&amp;#160;Meanwhile,&amp;#160;the&amp;#160;deformation indicated&amp;#160;a magma intrusion&amp;#160;in the area of the activity, showing a good correlation&amp;#160;with seismic data.&amp;#160;&lt;/span&gt;&lt;span&gt;Some&lt;/span&gt;&lt;span&gt;&amp;#160;hours before&amp;#160;the&amp;#160;eruption&amp;#160;started&amp;#160;there was a sudden&amp;#160;change in&amp;#160;the&amp;#160;migration&amp;#160;direction&amp;#160;pointing north&amp;#160;while&amp;#160;hypocenters considerably&amp;#160;accelerated its trend to the surface. This episode&amp;#160;was&amp;#160;accompanied&amp;#160;by&amp;#160;a rapid deformation of&amp;#160;more than&amp;#160;7&amp;#160;cm&amp;#160;to the&amp;#160;South&amp;#160;and&amp;#160;5&amp;#160;cm&amp;#160;upwards&amp;#160;in&amp;#160;the closest&amp;#160;GNSS station.&amp;#160;Finally,&amp;#160;4 hours before the eruption,&amp;#160;an increase&amp;#160;in the&amp;#160;shallow&amp;#160;seismicity rates&amp;#160;was observed. Most of the earthquakes were&amp;#160;not&amp;#160;felt by&amp;#160;the&amp;#160;island&amp;#160;population&amp;#160;and&amp;#160;moderate&amp;#160;magnitudes&amp;#160;were recorded reaching a maximum of&amp;#160;3.8&amp;#160;(mbLg).&amp;#160;InSAR&amp;#160;results during the whole process show more than 20 cm of deformation in LOS (Line of&amp;#160;Sight)&amp;#160;to&amp;#160;the South of the eruption vent.&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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&lt;p&gt;&lt;span&gt;Hours before the eruption, the seismicity behavior and the deformation shape indicate the existence of an intruding dike that culminated in eruption&amp;#160;and that would be the last stage of a magmatic process that had begun at least four years earlier with the seismic reactivations on the island.&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;
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