Sustained Long-lived Volcanic Subsidence at Timanfaya, Lanzarote, from InSAR Time Series

Abstract:

One of the most significant volcanic eruptions to occur on the Canary Islands, was the 1730–1736 eruption on Lanzarote. During the 2055-day eruption between 3 –5 km² (Carracedo, 2014) of material was erupted over an area greater than 200 km² (Solana et al., 2004). Since then there has only been one other volcanic eruption in 1824 and present-day activity is limited to anomalous heat flow over part of the 1730—1736 lava flows (Montanas del Fuego). Very few studies have looked at long term (centuries) volcanic deformation, but previous ERS InSAR (Gonzalez and Fernandez, 2011) and GNSS (Riccardi et al, 2018) measurements of the past few decades on Lanzarote showed an area of subsidence spatially correlated with the high heat flow.

Here we used over 400 Sentinel-1 and Envisat ascending and descending images to construct a time series of line of sight displacements and calculate linear deformation rates over the whole island. The ascending and descending deformation rates were decomposed to give vertical and E-W rates. The phase bias contribution of the shorter interferograms was also explored for the Sentinel 1 data using a range of short and longer temporal baseline networks. Thermal modelling was then used to investigate the potential cause of deformation almost 300 years after lava emplacement.

Our preliminary results show a constant subsidence rate of 6-7 mm/yr associated with the the south-east portion of the Timanfaya lava flows over the 28 year period (1992 – 2020) covered by the Sentinel, Envisat and ERS data. We examine a 1D thermal cooling model of a 278 – 284 year old lava with varying estimates of flow thicknesses to explore whether thermal contraction could have produced this deformation signal, and we also consider mechanical compaction of the lava flows as an alternative hypothesis. The possible constrains of a historic magmatic intrusion still cooling were also explored using Bayesian inversion. These results show that volcanic deformation can occur on longer timescales than previously thought and is still measurable centuries after volcanic events.