MASS FLUX AND MAGMA STORAGE AT THE LAGUNA DEL MAULE VOLCANIC FIELD, CHILE: MAGMA RESERVOIR EVOLUTION ON HUMAN TIMESCALES

The Laguna del Maule volcanic field (LdMvf), Southern Andean Volcanic Zone, Chile, is an active, highly silicic volcanic system affiliated with modern Andean subduction. The LdMvf has been studied for the last 25 years using a suite of methods due to its history of numerous high-volume, explosive eruptions. These methods include Bouguer and microgravity surveys, which enable direct observation of changes in subsurface mass flux. These gravity surveys contribute to previous interpretations that in addition to an actively emplacing sill, driving inflation rates greater than 20 cm/year, there are likely two other magma reservoirs in the region, which have been argued to have produced some of the more recent lava flows.

Previous Bouguer surveys, conducted between 2013 and 2018, imaged the actively inflating sill (Lake anomaly), and recognized two additional nearby magma reservoirs: 1) a potentially eruptible rhyolite mush and rhyodacite crystal concentrate (Barrancas anomaly) and 2) a poorly-resolved gravity anomaly (Cari Launa anomaly). Improved resolution from a 2024 Bouguer survey suggests the Cari Launa gravity anomaly has the same magnitude as the Barrancas anomaly, implying the LdMvf has a third magma reservoir of potentially eruptible mush. Annual microgravity surveys conducted from 2013 to 2016, interpret water flux into the region above the Lake anomaly. Additional microgravity surveys, conducted in 2017, 2018, and 2024, demonstrate that mass flux continues, motivating researchers to consider the consequences of water addition above the potentially eruptible Lake anomaly.

The integrated decadal gravity datasets reinforce the model that the LdMvf is a volcanic system with multiple spatially-discrete magma reservoirs actively evolving on human timescales. Gravity datasets with decadal resolution of active volcanoes are laborious and costly to collect but are one of the only methods by which mass flux can be directly measured in the subsurface, making them one of the best datasets for capturing rapid year- to decade-scale magmatic processes that are often lost in the rock record. In order to build more accurate models for the evolution of arc magmatic systems and make more informed interpretations of the plutonic record, a better understanding of rapid timescale (1–100 yr) processes must be built through datasets such as the LdMvf gravity data presented here.