Skip to content

Hydrothermal alteration and fluid circulation in a collapsing volcano (Askja caldera, central Iceland)

Florian Sfalcin 1, Kalin Kouzmanov1, Nicolas Oestreicher1,2,3, Antoine De Haller1, Tom Sheldrake1, Bhagyashree Mishra1, Frank Förster1, Joël Ruch1

  • Affiliations: 1Department of Earth Sciences, University of Geneva, Geneva, Switzerland; 2WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland; 3Climate Change, Extremes and Natural Hazards in Alpine Regions Research Centre CERC, Davos, Switzerland

  • Presentation type: Poster

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

  • Poster Board Number: 45

  • Programme No: 3.8.29

  • Theme 3 > Session 8

Abstract

Large caldera collapses are some of the most dramatic geological phenomena, often involving complex interactions between faults and hydrothermal fluid circulation. This study focuses on the Askja caldera (central Iceland) where a massive landslide occurred in 2014, exposing to surface a wide range of altered rocks, thus providing a unique opportunity to investigate the relationship between fluid circulations, alteration processes, and faulting.  Characterization of the different alteration styles within the landslide area aims to characterize the involved fluids and their compositions. This study also explores the potential interaction between structural features, such as caldera ring faults, and specific fluid circulations, as triggers to the landslide process.  We collected a series of samples during a field mission in August 2024, mostly within the products of the 2014 landslide, and identified their origin on the landslide wall.  The main types of alteration were identified affecting basalts and rhyolites (calcite, zeolite, pyrite, hydrothermal quartz). Petrography, XRF, XRD, optical-CL, Raman spectroscopy, QEMSCAN, microprobe and LA-ICP-MS have revealed that the observed alterations resulted from two distinct fluid systems circulating through the landslide area. Additionally, hydrogen and oxygen stable isotope analyses could help inferring the origins of these fluids, further elucidating their role in the alteration processes.  Our results shed light on the structural control of hydrothermal alteration in collapsed calderas, advancing our understanding of the mechanisms driving caldera instability and landslides.