“Breaking news” on the formation of volcanic ash: Fracture dynamics in silicate glass

In explosive volcanic eruptions magmatic melts behave like brittle solids under rapid loading: volcanic ash particles predominantly are generated by brittle fragmentation, induced within pre-stressed magma in volcanic conduits. Here we present straightforward measurements of fracture area velocity, i.e., surface generation rates in analog materials under “volcanic” time— and deformation rates, using a high resolution high-speed camera at up to 2.5 million frames per second. Surface generation rates are directly linked to energy dissipation and can be related to pyroclast formation during explosive volcanism. According to our findings, pre-existing stress fields play a crucial role for the evolution of cracks, control the dynamics of fracture area growths during fragmentation, and thus strongly modify the production of volcanic ash.

► Fracture experiments on glasses under volcanic deformation rates were performed.
► Surface generation was observed under high spatial and temporal resolution.
► Pre-existing stress fields in silicate melts significantly affect fracture dynamics.
► Pre-stresses determine the formation of volcanic ash.