Debris avalanche deposit of Temascalcingo volcano, Acambay graben, Mexico State

Abstract

The Temascalcingo volcano is located 70 km to the NW of Toluca city, and next to the town of the same name, in the State of México. It is one of several volcanoes within the Acambay graben. The Temascalcingo is an andesitic-dacitic stratovolcano, apparently of Pliocene age, with a summit caldera and affected by several normal faults of the Acambay Graben system. At the end of its volcanic evolution there was a destructive phase in the form of a lateral collapse, which formed a debris avalanche deposit and a lithics-rich pyroclastic flow deposit. This collapse occurred on the western flank of the volcano, leaving a horseshoe shaped amphitheater opened to the west and with a size of 6.5 by 3.5 km. The debris avalanche deposit is distributed on the same W direction, reaching at least 6 km from the source; includes hummocks up to 100 m high, and covers an area of 23 km2, representing a rock volume of 0.8 km3, including the exposed rocks in the hummocks. The lateral collapse of the Temascalcingo volcano is of Bezymianny type. The event was probably similar to that of the December 1997 eruption of Soufrière Hills volcano at Montserrat, and was caused by a combination of factors, including: 1) magma injection and emplacement of a lava dome that caused overpressure in the magmatic system and instability of the volcano, 2) an earthquake associated to the Acambay fault system that triggered the sector collapse of the volcano; and 3) fast depressurization related to the quick opening of the system by the landslide and the dome collapse that resulted in an explosive eruption that formed a block and ash pyroclastic flow and an eruptive column that formed a lapilli fallout.