Persistent Activity and Crater Formation at Telica Volcano Driven by the Shallow Hydrothermal System

<p>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 (sub-decadal) explosive, phreatic to phreatomagmatic eruptive activity. We are studying this system through the combination of geophysical, geochemical, and geologic observations and analyses. To date our observations and analyses indicate: 1) long-lived fumaroles and subsequent hydrothermal alteration of the crater walls lead to regions of preferential crater wall collapse into the active the crater; and 2) hydrothermal alteration and mineralization within the shallow hydrothermal system leads to sealing of the conduit, a build-up of pressure and explosions. The partial to complete sealing of the top of the volcanic conduit is thought to occur through the deposition of salts and silicate minerals from hydrothermal fluids, moving the volcano from an open to a closed system. The formation of a seal is observed indirectly by the eruption of hydrothermal mineral species and altered rock, decreases in measured gas flux, thermal anomalies, and LF seismicity that indicates a decrease in gas flow, and deformation of the volcanic edifice due to the increase in pressure from gas accumulation. Additionally, the eruption of a small volume lava dome in 2017 indicates the presence of highly viscous basaltic andesite magma in the conduit, which may also contribute to sealing of the conduit and the observed deformation. Here, we model cGPS displacement time series based on our conceptual model for the transition from an open to a closed system, utilizing our disparate, but complimentary data sets, including gas flux, terrestrial and remotely sensed thermal, web camera and cGPS displacement time series. Our numerical model incorporates changes in permeability of the conduit due to mineralization and the subsequent accumulation of gas beneath the seal. The increase of pressure due to sealing of the system and rising magma eventually leads to failure of the seal and phreatic explosions. Improving our knowledge of this transition from an open to closed system is important for understanding Telica&#8217;s eruptive processes and hazards, as well as gaining a better understanding of how this transition could manifest at other volcanic systems.</p>