CATASTROPHIC SEDIMENTATION ON THE EASTERN END OF THE MEXICAN VOLCANIC BELT

Volcanic activity at the eastern end of the Mexican Volcanic Belt has been very frequent during the last 2 Ma. The construction of large stratovolcanoes and other minor volcanoes formed the nearly N-S-trending Cofre de Perote-Citlaltépetl volcanic chain, which represents an important topographic barrier that separates the Central High-Plain (2,500 masl) from the Gulf Coastal Plain (1,300 masl). The abrupt relief between these physiographic provinces has favored unstable conditions with the subsequent catastrophic sedimentation derived mainly from the gravitational collapse of the large volcanic edifices. Large amounts of volcanic sediments have been produced in the last 0.5 Ma, and were widely spread preferentially towards the eastern flank of the volcanic range. The continuous sedimentation formed a relatively flat topography with a well-developed drainage and deep barrancas formed by thick volcaniclastic deposits that characterizes the Coastal Plain. Complex processes of sedimentation occurred during the transportation of the volcaniclastics producing lateral transformations from primary voluminous debris avalanche and lahar deposits to debris flows, hypoconcentrated and runout deposits. Most of the sedimentation is attributed to major catastrophic collapse-related events that have been identified in the stratigraphic record and are related to the major volcanic complexes such as Citlaltépetl, Las Cumbres, and Cofre de Perote volcanoes and perhaps also La Gloria volcanic complex. At least three major catastrophic events are associated with Citlaltépetl volcano, one of the largest deposits was formed from Las Cumbres volcanic complex, and two more from Cofre de Perote volcano. Also, a debris flow deposit was derived from the middle part of the volcanic range as a result of a strong earthquake in 1920. No direct evidence of magmatic activity has been found in relation to the origin of the catastrophic sedimentation. Therefore, other triggering factors such as: frequent seismic activity and high rain precipitation may be considered as well. Unstable conditions such as very intense hydrothermal alteration, abrupt topography and intense fracturing of the volcanic edifices have been strong in the past. Recurrence of new catastrophic events are very likely in the near future as those conditions are still affecting the volcanic range.