Timothy Davis , Marco Bagnardi , Paul Lundgren , Eleonora Rivalta 

Eruptions at shield volcanoes often occur from radially aligned linear fissures fed by blade-like magma-filled cracks (dykes). The fissures of the 2018 Sierra Negra eruption were scattered on the flank of the volcano. Space-borne radar interferometric data (InSAR) revealed that, unexpectedly, part of the eruption was fed by a 15 km long, tortuous and flat-lying crack (sill). Here we develop a framework that captures the full 3D kinematics of non-planar intrusions. This includes both an analytical and comprehensive numerical scheme. We constrain the models such that they match the observed ground deformation at Sierra Negra. We show that the peculiar sill trajectory is due to the competing stress gradient magnitudes being close to one another throughout its propagation. By accounting for the interaction of all these factors, these 3D models open the possibility to understand and simulate the geometry of magma transport at volcanic systems.