Revealing the unusually ‘silent’ precursors of the Fagradalsfjall volcano
In one paper, Freysteinn Sigmundsson, Michelle Parks, and colleagues investigated the precursors to the eruption. The study is critical because, before many eruptions, volcanoes exhibit an increase in activity, ie, an increase in the number of earthquakes and an increase in surface deformation. Both of which are related to magma forcing its way up through the shallow crust.
“Prior to the 2021 eruption at Fagradalsfjall, we, in fact, observed the opposite. Both a decline in seismicity and deformation in the few days before the eruption onset,” volcanologist Dr. Michelle Parks, lead author of the study, tells Interesting Engineering (IE).
New considerations for forecasting volcanic eruptions
The researchers in this paper propose that forces (stresses) are stored in the crust of the Earth prior to eruptions due to movements of the plates covering the surface of the Earth.
As the stored tectonic stress was released during the magma intrusion and associated earthquakes, there was less magma migration in the lateral (sideways) direction. This resulted in an observed decline in seismicity and deformation.
Essentially, the magma was forced to travel higher in the crust, which reduced the driving pressure and magma inflow rate. “The upper 1 km of the crust here is weak, so the magma was able to move towards the surface in a relatively silent manner, without any further increases in activity prior to the eruption onset,” explains Parks.
The findings demonstrate that the interaction between volcanic processes, tectonic stress, and crust composition needs to be considered when forecasting eruptions, the authors concludes.
Still, “precursors will be different for different volcanoes.” Dr. Michelle Parks reveals to IE.