Dynamics of a large dyke intrusion at Fentale in the Ethiopian rift

Only a few large dykes have been intruded during the era of modern satellite geodesy and as a result the dynamics of how dikes grow over many tens of km’s and interact with faults is poorly understood. Here we exploit the exceptional spatial and temporal resolution of InSAR during the December 2024-January 2025 Fentale dyke (Ethiopia) combined with seismicity and numerical models to study the dynamics of a large dyke intrusion. Our results show that a ~40 km long dyke fractured the entire Fentale-Dofen volcanic segment of the Ethiopian Rift from 19 December 2024 to 03 January 2025. The dyke first migrated laterally in just ~15 days but opening continued for a protracted period. Throughout the episode, melt was fed from a single reservoir beneath Fentale at the southern end of the segment. The dyke migration ended with the triggering of two earthquakes, a Mw 5.5 and 5.7 on the 3 and 4 of January, ~20 km beyond the dyke tip. Dyke opening and concomitant deflation at Fentale instead continued until the time of writing this abstract. The volume and seismic character of the Fentale dyke are comparable to other major rifting episodes observed at mature rifts and ridges, like the 2005 Dabbahu dyke, the 2014 Bardabunga dyke, and the ongoing Reykjanes episode. Our results support models of repeated magmatic rifting episodes being the main mode of plate boundary extension even in youthful continental rifts. Our observations are also in agreement with theoretical dyke propagation models in which faulting ahead of the dyke arrests its propagation.