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Influence of subsurface soil and lithology alteration on degassing at Krafla Caldera, Iceland

Roberto Davoli 1, Katharina Engels1, Cristian Montanaro1, Tullio Ricci2, Alessandra Sciarra2, Bettina Scheu1

  • Affiliations: 1 Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Theresienstrasse 41, 80333 Munich, Germany 2 Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma 1, Via di Vigna Murata 605, 000143, Rome, Italy 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 32

  • Programme No: 3.8.16

  • Theme 3 > Session 8

Abstract

Rock-fluid interactions significantly alter rock and soil properties, influencing fluid flow within hydrothermal aquifers, shaping surface features and degassing over time in geothermal settings. Understanding the spatial distribution of thermal manifestations in relation to geological settings and alteration types is crucial for revealing the processes that control fluid transport from subsurface aquifers to the surface. While past studies have focused on alteration effects within hydrothermal aquifers on a scale of hundreds of meters, limited research has examined the influence of subsurface lithologies, including their permeability (both intrinsic and altered) and spatial distribution on degassing activity. The present study investigates the relationship between subsoil lithologies and degassing zones in the active geothermal fields of Krafla caldera, Iceland. Specifically, it explores how hydrothermal alteration affects the petrophysical properties of these lithologies, thereby influencing surface fluid circulation. In 2022 and 2023, we conducted two field campaigns, assessing the in situ petrophysical properties of over 200 samples from 22 sites in the Víti and Hveragil regions. We also measured subsoil diffuse CO2 flux at specific profiles. Permeability values ranged from 10⁻¹¹ to 10⁻¹⁶ m², with CO2 fluxes varying from 1.25 to 2628.33 g m-² d-1. Grain size distribution and componentry analysis were performed on selected subsoils. Our findings reveal both active and inactive geothermal regions, illustrating the varying impacts of hydrothermal alteration. In active zones, mineral dissolution creates fluid flow pathways, while mineral cementation in inactive zones hinders fluid movement, providing key insights into the dynamics of fluid transport and degassing in geothermal settings.