Magmatic Processes in the East African Rift System: Insights From a 2015-2020 Sentinel-1 InSAR Survey

The East African Rift System (EARS) is composed of around 78 Holocene volcanoes, but relatively little is known about their past and present activity. This lack of information makes it difficult to understand their eruptive cycles, their roles in continental rifting and the threat they pose to the population. Although previous InSAR surveys (1990-2010) showed sign of unrest, the information about the dynamics of the magmatic systems remained limited by low temporal resolution and gaps in the data set. The Sentinel-1 SAR mission provides open-access acquisitions every 12 days in Africa and has the potential to produce long-duration time series for studying volcanic ground deformation at regional scale. Here, we use Sentinel-1 data to provide InSAR time series along the EARS for the period 2015-2020. We detect 18 ground deformation signals on 14 volcanoes, of which six are located in Afar, six in the Main Ethiopian Rift, and two in the Kenya-Tanzanian Rift. We detected new episodes of uplift at Tullu Moje (2016) and Suswa (mid-2018), and enigmatic long-lived subsidence signals at Gada Ale and Kone. Subsidence signals are related to a variety of mechanisms including the posteruptive evolution of magma reservoirs (e.g., Alu-Dallafila), the compaction of lava flows (e.g., Nabro), and pore-pressure changes related to geothermal or hydrothermal activity (e.g., Olkaria). Our results show that similar to 20% of the Holocene volcanoes in the EARS deformed during this 5-years snapshot and demonstrate the diversity of processes occurring.