ORIGIN AND DISTRIBUTION OF DIFFUSE SOIL CO2 GAS EMISSIONS ACROSS TURRIALBA AND IRAZÚ VOLCANOES, COSTA RICA

Author

Katie Nelson, Michigan Technological UniversityFollow

Date of Award

2021

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Geophysics (MS)

Administrative Home Department

Department of Geological and Mining Engineering and Sciences

Advisor 1

Chad Deering

Committee Member 1

Snehamoy Chatterjee

Committee Member 2

Florian Schwandner

Abstract

We characterized large-scale volatile emissions across the summit and flanks of the actively degassing Turrialba volcano, Costa Rica, using soil gas flux measurements and ¹³C isotopes. The objectives of this study were the following: 1) to monitor changes in the magmatic activity and identify source contributions over Turrialba using measurements of CO₂ soil gas emissions since the volcano last erupted in 2014-2015, and 2) to identify the location and extent of magma at depth, and the structures that allow gas transport to the surface. Degassing at the summit is concentrated along one normal fault lineament, the trace of which runs through the west active crater and fumarolic fields which lay on either side. The high soil gas flux measured, visible evidence of active degassing through fumaroles, and magmatic δ¹³C (up to -1.19‰) suggest permeability along this structure that gas follows from magma at depth. δ¹³C samples collected in and around fumaroles at the summit are more enriched than those collected within an area known for consistent fumarolic activity in the Ariete fault, which has also been used by previous studies as a baseline for hydrothermal-magmatic δ¹³C signatures (~-3‰). Additionally, there is a higher CH₄/CO₂ ratio present in the Ariete fault than at the summit. The difference in isotopic signatures between flank and summit fumaroles is interpreted to indicate magmatic-dominated activity at the summit of Turrialba, possibly comparable to that present at the end of the 2014-2015 eruptive cycle. A similar zone of high diffuse degassing with a more hydrothermal carbon isotopic signature (~-4‰) occurs in the depression between Turrialba and Irazú volcanoes, presenting as a hot spring known as Santa Teresa. We hypothesize the origin of CO₂ flux in this area to be related either to transport through the hydrological system from higher in the volcanic system or from previously unmapped magma at depth below the depression. More detailed mapping of soil CO₂ emissions must be done between Turrialba and Irazú in conjunction with geophysical monitoring to further advance our understanding of the magma distribution and potential magmatic connection between these volcanoes.

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Recommended Citation

Nelson, Katie, "ORIGIN AND DISTRIBUTION OF DIFFUSE SOIL CO2 GAS EMISSIONS ACROSS TURRIALBA AND IRAZÚ VOLCANOES, COSTA RICA", Open Access Master's Thesis, Michigan Technological University, 2021.

https://doi.org/10.37099/mtu.dc.etdr/1323