The 10.5 ka Plinian eruption of Nevado de Toluca Volcano, Mexico; stratigraphy and hazard implications
The 10.5 ka Plinian eruption of Nevado de Toluca Volcano, Mexico; stratigraphy and hazard implications
Geological Society of America Bulletin (February 2003) 115 (2): 230-248
- absolute age
- C-14
- carbon
- Cenozoic
- charcoal
- dates
- geologic hazards
- igneous rocks
- isotopes
- lahars
- mass movements
- Mexico
- Mexico state
- Nevado de Toluca
- phreatomagmatism
- Pleistocene
- plinian-type eruptions
- pumice
- pyroclastic flows
- pyroclastics
- Quaternary
- radioactive isotopes
- tephrochronology
- upper Pleistocene
- upper Weichselian
- volcanic risk
- volcanic rocks
- volcanoes
- Weichselian
- Younger Dryas
During the late Pleistocene, a large Plinian eruption from Nevado de Toluca volcano produced a complex sequence of pyroclastic deposits known as the Upper Toluca Pumice. This eruption began with a phreatomagmatic phase that emplaced a hot pyroclastic flow (F0) on the east and northern flanks of the volcano. Eruption decompressed the magmatic system, almost immediately allowing the formation of a 25-km-high Plinian column that was dispersed by winds predominantly 70 degrees to the northeast (PC0). Next, three other Plinian columns were dispersed in a northeast to east direction, reaching heights of 39, 42, and 28 km, resulting in fall layers (PC1, PC2, and PC3), respectively. These Plinian phases were interrupted several times by phreatomagmatic and collapse events that emplaced pyroclastic flows (F1, F2, and F3) and surges (S1 and S2), mainly on the eastern and northern flanks of the volcano. The eruption ended with the extrusion of a crystal-rich dacitic dome at the vent. The juvenile components of the Upper Toluca Pumice sequence are white, gray, and banded pumice, and gray lithic clasts of dacitic composition (63%-66% SiO (sub 2) ) and minor accidental lithic fragments. The fall deposits (PC1 and PC2) covered a minimum area of 2000 km (super 2) and constitute a total estimated volume of 14 km (super 3) ( approximately 6 km (super 3) DRE [dense-rock equivalent]). The mass eruption rate ranged from 3X10 (super 7) to 5X10 (super 8) kg/s, and total mass was 1.26X10 (super 13) kg. Charcoal found within Upper Toluca Pumice yielded an age of 10,500 (super 14) C yr B.P. (12,800-12,100 (super 14) C calibrated yr B.P.), somewhat younger than the earlier reported age of ca. 11,600 (super 14) C yr B.P. This new age for the pumice falls within the Younger Dryas cooling event. The eruption emplaced 1.5 m of pebble-sized pumice in the City of Toluca region and approximately 50 cm of medium to fine sand in the Mexico City region. Distal lahar deposits derived from the Upper Toluca Pumice event incorporated mammoth bones and other mammals in the basin of Mexico. A future event of this magnitude would disrupt the lives of 30 million people now living in these cities and their surroundings.