Geomorphic assessment of the debris avalanche deposit from the Jocotitlán volcano, Central Mexico

Abstract: Edifice collapse of the Jocotitlán volcano produced a debris avalanche deposit whose morphology is characterized by conical hummocks and elongated ridges. We consulted aerial photographs, orthophotographs, and conducted field work to define field relationships between mound morphology and stratigraphy. Based on field evidence and geomorphic and geologic interpretation we sub-divide the deposit into three sectors (north, northeastern, and eastern). We determine the emplacement mechanisms of the different sectors based on their distinct morphologic and lithologic features. In this context, we generate a geomorphometric database comprising 17 variables for each mound and apply multivariate statistical methods (principal component analysis and cluster analysis) to define the relationships between them. The principal components incorporated 73% of the total data variance and seven geomorphometric variables (perimeter, major axis, area, height, distance to the source, axis ratio and circularity index) defined two groups: hummocks and ridges. The circularity index and the axis ratio best characterize the elongated form of hummocks composing the deposits. Contrasts in lithological characteristics, such as material strength and mobility, provide evidence for a transition from a sliding mass (debris avalanche deposit) to a debris-flow-like emplacement. Differences in deposit morphology suggest two collapse mechanisms: magmatic intrusion (Bezymianny-type sector collapse) and a tectonic mass-slide, an earthquake could provide the trigger for both collapses. The eastern lower flank of the volcano then collapsed gravitationally due to a movement along a fault (tectonic activity possibly related to the Acambay–Tixmadeje Fault System). This produced the northeastern sector of the debris avalanche deposit dominated by large elongated ridges. The spatial arrangement of both sectors (the N and NE) suggests that the two failure events occurred simultaneously. Finally, the eastern sector of the deposit was emplaced by posterior remobilization of material from the two other sectors through a debris flow. [Copyright &y& Elsevier]