Multidisciplinary investigation of the evolution of persistently active basaltic volcanoes

The size, shape, location and/or chemical evolution of basaltic magma plumbing systems at most volcanoes is not well constrained. Having this information beneath active systems allows scientists to target areas which will likely be the first to display volcanic unrest. With these constraints and datasets that cover long periods of time or include anomalous topographic features, we can start to investigate how a volcanic system has changed over time. To accomplish this, geochemical and geophysical studies at Masaya volcano (Nicaragua) and Mauna Loa volcano (Hawaii, USA) were conducted. Melt Inclusions were collected from Masaya volcano to investigate the processes within the magma chamber. The almost unchanging chemistry of the whole rock, crystals and melt inclusions regardless of which eruptive cone sampled suggests that the system is buffered in both temperature and chemistry. A large deep reservoir with rapid transit times to the surface could explain the data. Bouguer gravity mapping data at Masaya and Mauna Loa volcanoes were collected, processed and inverted to constrain the location and volumes of density anomalies at depth. Beneath Masaya volcano, the gravity data provides evidence of a very large intrusive complex (< 900 km3) at 4-9 km depth as well as several small shallow anomalies perhaps due to ring dykes around a buried caldera rim. This study strengthens arguments that Masaya does not have a large shallow magmatic system and that shallow endogenous growth is minimal. Gravity mapping and inversions from Mauna Loa provide evidence for relatively rapid rift zone migration most likely caused by a large edifice destabilizing event. The massive Ālika debris flows are contemporaneous with the age of rift zone migration suggesting that mass wasting is the cause.