Effective mapping of large ignimbrites by using a GIS-based methodology; case of the Xáltipan ignimbrite from Los Humeros caldera, Mexico

Abstract

The Xáltipan ignimbrite (XI) records the largest single-eruption of the Trans-Mexican Volcanic Belt up to date (≥344 km3 uncompacted volume). As most large ignimbrites, the XI presents common challenges when mapping. These are abrupt welding variations, burial by younger units near other volcanic sources, and highly eroded deposits in active-water valleys. In this work, we deal with these issues by integrating classical cartographic techniques such as field measurements, geometric projections of energy lines and construction of geologic sections, with a GIS-based methodology that quantifies the eroded bulk. As a result, we obtained a map with the main XI features that is presented in an interactive format. Furthermore, we discuss the resources used for the map construction and how the results contributed to the interpretation of the eruptive history. These contributions include: 1) the energy lines point to a low-height pyroclastic density currents source, typical of caldera-forming, boiling-over eruptions; 2) the landscape of the XI, coupled with the geologic sections, indicate that in the proximal facies the ignimbrite filled a volcanic field, leaving a radially shaped distribution with a flat surface, while in the distal facies it channelized into a steep mountainous ground; and 3) the geologic sections in the valley areas, where the active rivers highly eroded the original XI deposits, revealed the preferential development of welded zones along channel centers.