EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Strength and permeability evolution of andesite during benchtop acid dissolution experiments: implications for volcanic systems

Jamie Farquharson1, Bastien Wild2, Alexandra Kushnir3, Michael Heap3, Patrick Baud3, and Ben Kennedy4
Jamie Farquharson et al.
  • 1Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, USA (
  • 2Andlinger Center for Energy and the Environment, Princeton University, Princeton, NJ, USA
  • 3Institut de Physique de Globe de Strasbourg (UMR 7516 CNRS, Université de Strasbourg/EOST), Strasbourg, France
  • 4Geological Sciences, University of Canterbury, Christchurch, New Zealand

Acidic crater lakes are common features of subaerial volcanic systems; indeed, research suggests the existence of over 700 volcanic lakes around the world. Their persistence requires a regular input of water (e.g., meteoric water) at a rate that exceeds the migration of fluid from the system—for example, due to evaporation or fluid flow through the porous edifice.  Flank aquifers and fumarole fields may similarly be strongly acidic environments.

In order to explore the evolution of the physical and mechanical properties of an andesite under these field-relevant chemical conditions, we performed batch reaction experiments over timescales from 1 day to 4 months. The experiments involved immersion of a suite of samples in a solution of sulfuric acid (0.125 M; pH ∼0.6). Periodically, samples were removed and their physical and mechanical properties measured. We observe a progressive loss of sample mass, along with a general increase in porosity. We attribute this to the dissolution of plagioclase,  accompanied by the generation of a microporous diktytaxitic groundmass due to glass dissolution.

Plagioclase phenocrysts are seen to undergo progressive pseudomorphic replacement by an amorphous phase enriched in silica and depleted in other, relatively more soluble, cations (Na, Ca, and Al). In the first phase of dissolution (i.e. between 1 and 10 days), this process appears to be confined to preexisting fractures within the plagioclase phenocrysts. Ultimately, however, these phenocrysts tend toward entire replacement by amorphous silica. We do not observe evidence of induced dissolution or alteration in the other mineral constituents of the material: pyroxene, cristobalite, and titanomagnetite, specifically.

Examining the required Klinkenberg corrections during permeability measurements, we quantitatively demonstrate that the relative aperture of flow pathways increases with progressive acid immersion, by as much as a factor of five. We propose that the dissolution process results in the widening of pore throats and the improvement of pore connectivity, with the effect of increasing permeability by over an order of magnitude relative to the initial measurements. Compressive strength of our samples was also decreased, insofar as porosity tends to increase.

We highlight broader implications of the observed permeability increase and strength reduction for volcanic systems including induced flank failure and related hazards, improved efficiency of volatile migration, and attendant eruption implications.

How to cite: Farquharson, J., Wild, B., Kushnir, A., Heap, M., Baud, P., and Kennedy, B.: Strength and permeability evolution of andesite during benchtop acid dissolution experiments: implications for volcanic systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-883,, 2021.