Análisis de las Condiciones Estructurales de Estabilidad en el ...

Abstract
This work represents a new proposal in relation to volcano flank instability. Furthermore,
one of the proposals is that sector collapse on extinct or inactive structures is possible
and new evidences of sector collapses not related to eruptive activity are presented here.
This work also proposes that the volcano could have been slowly destabilized enough to
become prone to collapse, supported along with documented historic cases which are
also reviewed in the present work.
Cofre de Perote volcano (19° 30’N; 97° 10’ W, peaks at 4,650 m.a.s.l) conforms the
northern end of a volcanic chain known as Citlaltépetl-Cofre de Perote volcanic range
(CCPVR). Aligned with Cofre de Perote volcano, the southern end is represented by
Citlaltépetl volcano. The volcanic range forms an important physiographic barrier which
separates the central altiplano, also known as Cerdán Oriental, from the coastal plains of
Golfo de México. Contrary to common descriptions, Cofre de Perote volcano (CP) is not a
stratovolcano as it has been suggested in most references, but in reality an entire volcanic
complex conformed by a series of superimposed domic structures characterized by a soft
morphology which resemble a shield volcano. Its last activity has been determined as 0.2
My which implies that the structure can be considered as extinct.
Despite the mentioned conditions of the volcano, which suggest a stable structure with
no possibility of presenting any type of volcanic hazard to nearby populations, geologic
evidence represented by prominent fresh scarps at its summit along with avalanche and
debris flow deposits on its eastern slopes indicate that the volcano has suffered repeated
collapse events on recent times long after its ceased activity.
This scenario suggests the possibility that events of this nature, can recur in the future in
spite it is an extinct structure. This work presents an analysis of instability conditions of the
volcanic massif, attempting to evaluate the possibility of a recurrent event. The analysis
is based on the knowledge of the geologic characteristics of the volcano and its structural
behavior. furthermore, the work considers the loss of structural strength due to exposure
to hydrothermal fluids, being this one of the determinant factor favoring instability at the
volcanic massif and in absence of a magmatic component.
Mineralogy identified at the volcano and the debris flow and avalanche deposits suggest
that the structure may had been weakened due to interaction of the rocks with hydrothermal
fluids. It is also evident that weakening has not been thoroughly, showing zones of intense
alteration contrasting with areas relatively fresh. main structural difference of hydrothermal
alteration from that provoked by atmospheric erosion, is that this is more intense affecting
the structure to an undetermined depth.
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