How do surface displacements reflect the structure of volcanic plumbing systems below?

Volcanic plumbing systems comprise a complex series of interconnected intrusions (sills and dykes), which store and transport magma laterally and vertically. The movement of magma within these systems can be inferred using geophysical and geodetic techniques. Surface displacement measurements are one of the most common tools used to monitor the state of volcanoes, where ground motion can be related to inflation and deflation of magma reservoirs at depth and therefore record potential precursors that help forecast an eruptive event. Satellite-based interferometric synthetic aperture radar (InSAR) and global navigation satellite system (GNSS) provide data for surface changes on a near-daily basis; however, interpretation of deformation sources and mechanisms is limited by modelling approaches.  Inversion models (such as the Mogi model) are often used to interpret surface displacements in terms of the underlying structures, but these rely on assumptions and simplifications that may result in inaccurate estimations of intrusion sizes and volumes of eruptible magma.

To address this gap in understanding, we have developed a new synthetic volcano observatory to monitor scaled analogue volcanic plumbing system experiments. The first experiments we have tested include the simplest scenario for volcanic plumbing: a transparent gelatine solid (homogeneous or layered elastic crust analogue) injected by water (a Newtonian fluid magma analogue) to form an intrusion (a dyke or a dyke-fed sill). Over the course of the experiment, surface deformation is monitored using two CCD (charge-coupled device) cameras positioned above the tank, which track the vertical and lateral displacements of passive-tracer particles placed on the surface of the gelatine. Deformation of the surface above the dyke comprises an elongated central depression directly above the propagating tip of the dyke and parallel to its strike, and two inflated domes on either side of the elongated depression. In contrast, deformation of the surface above the sill forms a single inflated dome, with the area of greatest deformation centred above the connection between the sill and its feeder dyke. By analysing the experimental data with the same inversion approach used on natural magma intrusion events, we can explore how well factors such as intrusion geometry, depth, and volume are resolved, and how modelling algorithms can be improved to enhance volcanic eruption forecasting.