Textural studies of vesicles in volcanic rocks: An integrated methodology

Vesicles in volcanic rocks are frozen records of degassing processes in magmas. For this reason, their sizes, spatial arrangements, numbers and shapes can be linked to physical processes that drive magma ascent and eruption. Although numerous techniques have been derived to describe vesicle textures, there is no standard approach for collecting, analyzing, and interpreting vesicular samples. Here we describe a methodology for techniques that encompass the entire data acquisition process, from sample collection to quantitative analysis of vesicle size and number. Carefully chosen samples from the lower, mean and higher density/vesicularity endmembers are characterized using image nesting strategies. We show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes. A new program (FOAMS) was designed to perform the quantification stage, from vesicle measurement to distribution plots. Altogether, this approach allows substantial reduction of image acquisition and processing time, while preserving enough user control to ensure the validity of obtained results. We present three cameo investigations — on basaltic lava flows, scoria deposits and pumice layers — to show that this methodology can be used to quantify a wide range of vesicle textures, which preserve information on a wide range of eruptive conditions.