Reconstruction of the eruptive event associated to the emplacement of the 13 ka El Refugio pyroclastic flow, Nevado de Toluca volcano (Mexico)

Abstract

The Nevado de Toluca is a quiescent volcano located in the central sector of the Trans-Mexican Volcanic Belt, 80 km southwest of Mexico City. The activity began ca. 2.6 Ma ago, with andesitic to dacitic lava flows and domes that lasted until 1.15 Ma. During the last 42 ka, the volcano has been characterized by different eruptive styles, including five dome collapses dated at 37, 32, 28, 26, and 13 ka and five plinian eruptions at 42 ka, 36 ka, 21.7 ka, 12.1 ka and 10.5 ka.

The 13 ka dome destruction is the youngest event of this type, and originated a 0.11 km3 block-and-ash flow deposit on the northeastern sector of the volcano, here named El Refugio flow. The deposit consists of two facies: channel-like, up to 10 m thick, monolithologic, that is composed of up to five units, with decimetric dacitic clasts set in a sandy matrix; and a lateral facies that consists of a gray, sandy horizon, up to 4 m thick. A 30 cm-thick surge layer lies down at the base of the sequence. The main component is a dacitic lava, with variable degree of vesciculation, with mineral association of Pl-Hbl-Opx. Stratigraphic and petrographic features indicate that the dome was quickly extruded on the summit of the volcano, and its collapse was accompanied by an explosive component. The magmatic process that probably triggered the eruption was an overheating of the magma chamber that induced a self-mixing mechanism yielding to an overpressurization of the system. Finally, the identification of an explosive component associated with dome destruction events at Nevado de Toluca volcano clearly indicate the high risk that a future event with such characteristics can represent for populated areas around the volcano.