ALBERT

Description: Telica volcano is a persistently restless volcano with activity expressed as long-lived high-temperature fumaroles and magmatic degassing, high rates of background seismicity and frequent phreatic to phreatomagmatic eruptions. Two decades of geophysical, geochemical, and geologic observations indicate: 1) long-lived fumaroles cause hydrothermal alteration and collapse of crater walls, and deposition of debris in the crater; 2) decreases in gas flux, fumarole temperatures, remotely sensed thermal anomalies, and low-frequency seismicity prior to explosions and eruption of hydrothermal minerals and alteration products indicate sealing of the shallow hydrothermal system and conduit; and 3) eruption of a lava dome and ballistic blocks indicate viscous basaltic andesite magma in the conduit. Deposition of crater wall debris may seal the system at a shallow level but does not affect the deeper magmatic – hydrothermal system. Whereas the partial to complete sealing of the volcanic conduit occurs through the deposition of hydrothermal minerals, and the slow migration of viscous magma. These processes move the volcano from an open to a closed system, resulting in phreatic to phreatomagmatic explosions. We developed a numerical model to investigate near-field surface deformation measured by cGPS. Our model incorporates changes in permeability of the conduit due to mineralization, the accumulation of gas beneath the seal, and subsequent increase in pressure of the system driving surface deformation. Increase in pressure leads to failure of the seal and explosions. Improving our knowledge of this transition from an open to closed system is important for forecasting explosive activity at Telica and similar volcanic systems.

Description: Northwest-directed motion of the Central American Forearc at ~14 mm/yr relative to the Caribbean plate is accommodated on margin normal and parallel fault systems within the Central American Volcanic Arc in Nicaragua. Proximity of faults to magmatic systems has historically led to magma-tectonic interactions. Here, we present two cases. The 1999 eruption of Cerro Negro volcano was preceded (~11 hrs) by four ~M5.2 earthquakes. Coulomb failure stress modeling indicates the earthquakes reduced normal stress on the Cerro Negro-Cerro La Mula volcanic alignment leading to magma migration and eruption along an ~100 m long fissure. The 2015-2016 eruption of Momotombo was preceded by the April 10, 2014 M〈sub〉w〈/sub〉 6.1 earthquake, which displaced the flank of the volcano southward by ~6 cm. We use GPS-derived co-seismic displacements and relocated earthquake aftershocks to study the April 10, 2014 earthquake. The earthquake dilated (10s of µStrain) and reduced the normal stress on the shallow magmatic system of Momotombo volcano, leading to magma injection, ascent, and eruption on December 1, 2015, after ~110 years of quiescence. Geochemical and petrologic analyses of erupted products (ash and lavas), including major and trace elements, crystal-size distribution, geobarometry and elemental profiling across phenocrysts confirm the eruption of the high crystallinity (30-50%), high viscosity (10〈sup〉4〈/sup〉 Pa s) basaltic andesites was triggered by injection of new magma. These events represent the potential for cascading hazards in a forearc-arc system, with earthquake and magmatic triggering over short spatial (10’s km) and temporal (yrs) scales.