Models of deep interaction between volcanic systems during volcanic unrest and its implications for lower crustal structure and processes: Insights from the Reykjanes Peninsula, SW-Iceland

Understanding the transport of magma below the Earth’s surface is a key to studying volcanic systems. However, processes taking place at large depths are increasingly difficult to infer, since signals are often obscured by shallower processes. The Reykjanes Peninsula is an oblique rift zone in SW-Iceland and hosts several en-echelon arranged volcanic systems that experience contemporaneous rifting episodes over the course of 200-400 years. This episodic behaviour alternates with phases of volcanic quiescence lasting 800-1000 years. The occurrence of several eruptions since 2021 indicates the onset of a new phase of volcanic activity. Seismic and geodetic observations during recent years indicate that while at most one volcanic system appears to be active at any time on the peninsula, the focus of activity may shift abruptly between systems. Furthermore, while activity has focused on the Svartsengi volcanic system in 2023, the neighbouring Krýsuvík volcanic system has subsided at variable rates, indicating some degree of connection or communication between the systems.

We test this hypothesis of potential deep-seated communication by implementing lumped-parameter- and Finite Element models where the mid- to lower crustal magmatic plumbing systems within individual volcanic systems, connect to a zone underlying the peninsula near the crust-mantle boundary. This zone is thought to consist of discrete melt lenses, mush, partial melt and hot, ductile rock, and is rheologically weaker than its surroundings. The zone’s increased compliance relative to that of layers above and below allows for the transmission of pressure from one system to another. Pressure transfer does not require significant flow of material to occur between systems, allowing each volcanic system to keep its distinct geochemical characteristics.

In accordance with previous studies, the lumped parameter models represent the peninsula-scale magmatic system through several mid-crustal and one underlying, deep magma domain, all of which are connected through conduits and consist of melt lenses, mush and hot rock. The models reproduce several observed dynamics, including the temporary focus of activity on a single volcanic system, potential passive reactions in neighbouring systems, and abrupt transitions of activity between systems. Furthermore, the models underline the importance of considering processes and properties of the shallow plumbing system as well as volcano-tectonic interaction for deeper processes.