Short-period volcanic gas precursors to phreatic eruptions: Insights from Poás Volcano, Costa Rica

Earth and Planetary Science Letters
By: , and 

Links

Abstract

Volcanic eruptions involving interaction with water are amongst the most violent and unpredictable geologic phenomena on Earth. Phreatic eruptions are exceptionally difficult to forecast by traditional geophysical techniques. Here we report on short-term precursory variations in gas emissions related to phreatic blasts at Poás volcano, Costa Rica, as measured with an in situ multiple gas analyzer that was deployed at the edge of the erupting lake. Gas emitted from this hyper-acid crater lake approaches magmatic values of SO2/CO2 1–6 days prior to eruption. The SO2 flux derived from magmatic degassing through the lake is measureable by differential optical absorption spectrometry (sporadic campaign measurements), which allows us to constrain lake gas output and input for the major gas species during eruptive and non-eruptive periods. We can further calculate power supply to the hydrothermal system using volatile mass balance and thermodynamics, which indicates that the magmatic heat flux into the shallow hydrothermal system increases from ∼27 MW during quiescence to ∼59 MW during periods of phreatic events. These transient pulses of gas and heat from the deeper magmatic system generate both phreatic eruptions and the observed short-term changes in gas composition, because at high gas flux scrubbing of sulfur by the hydrothermal system is both kinetically and thermodynamically inhibited whereas CO2gas is always essentially inert in hyperacid conditions. Thus, the SO2/CO2 of lake emissions approaches magmatic values as gas and power supply to the sub-limnic hydrothermal system increase, vaporizing fluids and priming the hydrothermal system for eruption. Our results suggest that high-frequency real-time gas monitoring could provide useful short-term eruptive precursors at volcanoes prone to phreatic explosions.

Study Area

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Short-period volcanic gas precursors to phreatic eruptions: Insights from Poás Volcano, Costa Rica
Series title Earth and Planetary Science Letters
DOI 10.1016/j.epsl.2016.02.056
Volume 442
Year Published 2016
Language English
Publisher Elsevier
Contributing office(s) Volcano Science Center
Description 10 p.
First page 218
Last page 227
Country Costa Rica
Other Geospatial Poás Volcano
Online Only (Y/N) N
Additional Online Files (Y/N) N