Quantifying compaction deformation of volcaniclastic deposits
Edgar U. Zorn, Jackie E. Kendrick, Anthony Lamur, Janine Birnbaum, Ulrich Kueppers, Marize Muniz da Silva, Yan Lavallée
Affiliations: Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Theresienstraße 41, 80333 München, Germany
Presentation type: Poster
Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall
Poster Board Number: 105
Programme No: 3.15.10
Abstract
Volcaniclastic materials may compact by gravitational loading under their own weight or due to burial by new deposits, leading to subsidence. We experimentally investigate the compaction of volcaniclastic granules using two lithologies (scoria and hyaloclastite) of different grain size (ash and lapilli). Samples were confined in a cylindrical container, and then compressed between two pistons to target stresses of 2, 5, 10, or 20 MPa, measuring axial displacement. Samples were also loaded and held at each target stress for six hours, measuring additional time-dependent creep compaction. Strain rates were highest during the early loading stages and gradually slowed with increasing compaction as porosity reduction plateaued. Lithology and grain size both influenced compaction, dependent on the relative contributions of (I) grain rearrangement, controlled by size distribution, and (II) comminution, dependent on both size and material strength. Interpolation and extrapolation of the data were used to forecast surface deformation for volcaniclastic deposits of different thicknesses. Here, burial up to 2 MPa (equivalent to a deposit thickness of ~180--230 m) is projected to cause a (near instantaneous) surface subsidence of 24--55 m, with creep adding another ~1--3 m subsidence within less than a year. The findings suggest that compaction may account for significant post-eruptive deformation and emphasises the need to investigate volcaniclastic materials and their properties to improve our assessment of flank instabilities.