Publication Date:
2022-06-09
Description:
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 CO2 gas 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 highfrequency real-time gas monitoring could provide useful short-term eruptive precursors at volcanoes
prone to phreatic explosions
Description:
Published
Description:
218-227
Description:
2V. Struttura e sistema di alimentazione dei vulcani
Description:
4V. Dinamica dei processi pre-eruttivi
Description:
5V. Dinamica dei processi eruttivi e post-eruttivi
Description:
6V. Pericolosità vulcanica e contributi alla stima del rischio
Description:
JCR Journal
Keywords:
04.08. Volcanology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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