Tracking magma pathways and surface faulting in the Southwest Rift Zone and the Koaʻe fault system (Kīlauea volcano) using photogrammetry and structural observations

Abstract

Abstract Volcanic islands are often subject to flank instability, resulting from a combination of magma intrusions along rift zones, gravitational spreading and extensional faulting observed at the surface. Here we study the Kīlauea volcano in Hawaiʻi, one of the most active volcanoes on Earth, prone to flank instability. Two rift zones and the Koaʻe fault system are major structures controlling volcano flank instability and magma propagation. The connection between surface faulting and magma intrusions at depth is poorly studied despite the importance of faults in controlling magma pathways and forecasting future eruptions. In March 2022, we completed a helicopter photogrammetric survey covering part of the south flank of Kīlauea. We generated a high-resolution DEM (~ 8 cm) and orthomosaic (~ 4 cm) to map the fracture field in detail. We also collected ~ 1000 ground structural measurements of extensional fractures during our three field missions (2019, 2022, 2023) to better understand the kinematics of the Kīlauea’s south flank. In our analysis, we include many small, interconnected grabens, monoclines, rollover structures, and en-echelon fractures that were in part previously undocumented. Additionally, we estimate the cumulative displacement across the Koaʻe fault system during the last 600 years and found an average of 6 cm and 3 cm per year for vertical and horizontal directions, respectively, consistent with short-term GNSS data. These data provide a clearer picture of the structural linkages between the fault zone, which is largely a tectonic feature, and the rift zones, which are largely magmagenic. Finally, we propose a kinematic model of Kīlauea’s south flank suggesting a clockwise rotation and translation of a triangular wedge in response to the gravitational spreading and the nearby rift zones.