The Added Value From 4D Volcano Gravimetry: Lessons Learned From 20 Years of Observations

Abstract:

Microgravity studies represent a relatively underutilized technique to investigate active volcanoes compared to some of the more established methods (e.g. seismic and ground deformation). Temporal changes of the gravity field in volcanic zones are related to sub-surface mass redistributions in response to magmatic processes and are variable in space (wavelengths between hundreds of meters and tens of kilometers) and time (periods between seconds and years), according to the size, depth and rate of evolution of the source processes. As a result, both campaign and continuous gravity observations can make valuable contributes to better understanding how volcanoes work.

Gravity measurements offer insights into volcanic activity that cannot be inferred from other data sets. By supplying information on the subsurface mass distribution, gravity studies alleviate ambiguity on the nature of magmatic sources, which may affect the interpretation of ground deformation and other measurements. Gravity studies can detect magma accumulation in pre-existing void space, which does not produce any other measurable effect at the surface. Gravity surveys can also identify zones of increased microfracturing rate within a volcanic edifice, which may be able to channel magma from a deep storage area to the surface. Continuous measurements of the gravity field can recognize rapid changes in the magma/gas ratio within the upper plumbing system of a volcano and can thus be used to discover otherwise “hidden” states of unrest at active volcanoes. Continuous gravimetry can also track convective overturns in a shallow reservoir over short time scales.

Despite the obvious potential of gravity monitoring, gravity measurements at active volcanoes are still relatively rare, mainly due to instrument cost and data interpretation issues. Here, the potential of gravity studies to provide insight into the processes that drive volcanic activity will be shown through case studies from different volcanoes.