An integrated methodology to investigate vesicle textures in volcanic rocks: II-Applications

Textural studies involve a large number of time-consuming steps that include sample collection, measurement of bulk vesicularity and density, acquisition of series of microscopic images and, finally, measurement and conversion of bubble size and number data. Thus, development of automation tools that allow faster completion of one or more of these phases is crucial. A new Matlab-based user-friendly program named FOAMS (Fast Object Analysis and Measurement System) was recently designed to perform the quantification stage, from vesicle measurement to visualization of distribution plots, and reduce substantially the processing time required. Using three cameo investigations made on effusive basaltic lava flows, mildly explosive scoria deposits and powerfully explosive pumice fall layers as examples, we present the main steps involved in performing FOAMS runs, and show that it can be routinely applied to a wide range of products and bubble sizes from various eruption styles. In particular, we discuss how different choices in measurements parameters such as number of images used, minimum and maximum magnification chosen and minimum vesicle diameter measured all affect the outcome with choices depending on the type of volcanic clast under investigation. Vesicle size distribution plots for samples collected at three eruption sites (Makapuu lava flows, Villarica scoria, and Vesuvius 79AD pumice) in terms of volume fraction (above) and cumulative number density (below). Dotted lines delineate the portions of the distribution which are resolved for different choices of minimum imaged diameter (5, 10 or 20 pixels). Shaded areas correspond to errors associated with selection of minimum diameter.