3D Model of the Shallow Crustal Density Distribution of the Krafla Volcanic System in Iceland

Abstract

Krafla volcano, located in Iceland's North Volcanic Zone, has been extensively studied using static gravity surveys since 1975. This study integrates measurements acquired between 2022 and 2023 with legacy data to produce a new gravity map of the area. We produce gravity gradient maps to delineate shallow subsurface density features and invert them to develop a 3D density model that images key subsurface structures. The combined survey coverage, extending from Fremrinámar to the Þeistareykir Volcanic Systems, reveals a range of features with contrasting densities which reflect the tectonic and volcanic processes that have shaped the area. Denser materials are associated with mafic intrusions along the principal faults related to caldera-subsidence and ancillary faults within the caldera. In the Iceland Deep Drilling Project 1 (IDDP-1) area, located inside the caldera, we identify a positive density anomaly at depths corresponding to magma encountered during drilling at 2.1 km depth. Negative gravity anomalies, indicative of relatively low-density materials, are distributed within and outside the Krafla caldera. Within the caldera, these anomalies are interpreted as felsic intrusions and highly fractured geothermal zones. Beyond the caldera, a prominent negative density anomaly corresponds to the graben structure associated with the Húsavík-Flatey Fault. Although strong near-surface gravity anomalies and the spatial distribution of our gravity measurements limit the identification of deeper structures (>5 km), this study offers valuable insights into the distribution of the magmatic system features, as well as large tectonic characteristics in the area. These insights improve our understanding of magmatic and tectonic processes, volcanic hazards, and the future development of geothermal production in the area.