Near real-time dike tracking using GNSS networks

Volcanic activity can take several forms ; one of them is magma moving horizontally along the crust and forming a dike, i.e. subvertical magma-filled structures. Dikes pose substantial risk to population and infrastructure at the surface. They can transport the magma far away from the main volcanic edifice and result in eruptions in unexpected locations. The larger dikes will also induce surface faulting and even the formation of grabens. However, this means that we can measure this deformation at the surface to infer characteristics of the dike. This is traditionally done after the dike as finished propagating by using a combination of GNSS and InSAR measurements.

In Iceland, there have been 6 dikes intrusion on the Reykjanes Peninsula since 2021. The first four dikes occurred in uninhabited areas, originating from the Fagradalsfjall volcanic system. The last two dikes, in November and December 2023, originated from the Svartsengi volcano and are along an axis that goes partly under the town of Grindavik. All these dike intrusions have been recorded by the local continuous GNSS network. We tested the applicability of near real-time tracking of the dike propagation for all of these events. This is done by searching for the best-fitting Okada dislocation that explains the GNSS displacements, with some assumption about the origin and direction of the magma. The earlier events cannot be easily tracked because the GNSS network was too sparse. However, the network has been densified with time and the later events are easier to track. For the largest one, in Nov. 2023, we are able to observe the initial vertical propagation of the magma, its horizontal propagation to the SW and the NE, and its focus to SW at the end. We can measure the magma inflow rate within the dike hour by hour through the event. It peaks at over 9000 m³/s two hours after the beginning of the event. These results show that, given a network of a few continuous GNSS stations, it is possible to have a near real-time monitoring of a dike. Having this information would be extremely valuable to the decision takers and the civil protection. Therefore, it is planned to have this tool implemented at the Icelandic Met Office in the coming weeks to be able track future events. It will be set up for specific volcanoes and run automatically based on real-time GNSS solutions.