The ups and downs of the Lascar crater floor, and the resulting fracture pattern analyzed by satellite stereo photogrammetry and 3D printed mould analog experiments

Lava emplacement in a summit crater is often associated with unpredictable explosions and volcanic hazards, especially for volcanoes that are popular with tourists. The Lascar volcano, Chile, experienced a sudden eruption in December 2022, followed by the extrusion of lava. We acquired a series of Pleiades tri-stereo satellite images covering this new eruptive episode. Using a photogrammetric approach, we generated high resolution point clouds and orthomosaics from the satellite images. By directly comparing distances between point clouds, we are able to quantify morphological and structural details and changes. We find initial uplift of the crater floor due to lava extrusion and rockfall deposits, and evidence for subsidence and the formation of a funnel centered on the crater floor. To understand the mechanical factors controlling the uplift and subsidence of the crater floor, we designed a novel set of analogue experiments to simulate lava extrusion and subsidence inside a scaled 3D printed mould of the Lascar crater. We account for geometric and topographic effects by running these extrusion and subsidence models. Sand and sand-plaster mixtures extrude and subside from a vertical conduit at a constant rate, simultaneously recorded by a digital camera at 10-second intervals. We use particle image velocimetry (PIV) method to track and visualize displacements on the crater floor. The results show that extrusion and subsidence occurs along distinct shear faults, which are constrained by the diameter of the underlying conduit. The shear faults are represented as concentric fractures and are consistent with the ring features observed at Lascar. By comparing satellite observations with analogue models, we develop a conceptual model in which a lava extrusion is affected by withdrawal from the conduit, forming a funnel-shaped surface depression associated with inward-dipping radial erosion gullies. Thus, our observations and analogue models also help to define the position and dimensions of the volcanic conduit, which is essential for understanding future episodes of the ups and downs of the Lascar crater floor.