Three‐dimensional investigation of volcanic textures by X‐ray microtomography and implications for conduit processes

Abstract

[1] Synchrotron X-ray computed microtomography (mCT) was applied for the first time to clasts of pumice and scoria generated by active, explosive volcanoes characterized by a range of eruptive styles (mild Strombolian to Plinian) and magmatic composition (basaltic to trachytic). The obtained two-dimensional (2D) tomographic images, corresponding to sample views at different rotation angles, were processed to reconstruct three-dimensional (3D) volumes and then used to make 3D measurements of vesicularity, vesicle number density, volume and connectivity for quantitative characterization of the investigated tephras. The results indicate a positive correlation between vesicle number density and eruption intensity that is used to investigate modes of magma degassing in explosive eruptions. In addition, the vesicle geometry affecting the connected gas flow pathways in pyroclasts from Strombolian eruptions is determined and related to the known permeabilities. Implications on the dynamics of explosive eruptions is discussed and, ultimately, used to quantitatively discriminate between different eruptive styles.

The contribution of synchrotron X-ray computed microtomography to understanding volcanic processes

“…However, because it provides no direct information in the third dimension, this approach cannot be used to investigate the true internal structure of volcanic materials, limiting the information that can be provided on vesiculation, degassing and crystallization processes, as well as on the overall eruption dynamics. Recently, the application of X-ray computed microtomography (mCT) to geological specimens (Song et al, 2001;Ketcham et al, 2005;Gualda & Rivers, 2006;Polacci et al, 2006) has opened the opportunity to completely visualize and quantify the internal structure of porous materials, such as volcanic scoria and pumice clasts, directly in three dimensions. In this framework, a few years ago we started a project with the goal of performing X-ray microtomographic analysis and reconstructing three-dimensional (3-D) digital volumes of volcanic specimens.…”

High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications

“…Since micro-CT allows the measurements of the surface area and the volumes of individual ash particles, both this technique and SEM stereoscopic imaging are suggested by Ersoy et al (2010) to be good candidate techniques for the characterization of textures on macro-pore regions of ash particles. Polacci et al applied X-ray micro-CT to clasts of pumice and scoria from Stromboli, Villarica and the Campanian ignimbrite (Polacci et al, 2006) and samples of scoria and pumice from normal and paroxysmal activity at Stromboli (Polacci et al, 2009). Gualda and Rivers (2006) presented crystal size distributions for pumice clasts from the Bishop Tuff (California).…”

Heterogeneous vesiculation of 2011 El Hierro xeno-pumice revealed by X-ray computed microtomography

“…Reconstruction of 2D slices from the X-ray projections was performed by the commercial software COBRA (Exxim, USA), which is based on the FDK algorithm (Feldkamp et al 1984). For further methodological details of the experimental setup and of the reconstruction procedure, see Ketcham and Carlson (2001) and Polacci et al (2006Polacci et al ( , 2010.…”

“…To avoid biasing from texturally complicated micro-XCT images, pre-and post-segmentation smoothening filters were required on occasion to ease or refine the segmentation procedure (see Supplementary Table 2, cf. Polacci et al 2006;Brun 2012). The 3D anisotropic diffusion filter was applied by the Pore3D software to smooth the greyscale input images prior to segmentation, while preserving object edges (cf.…”