Influence of Nevado de Toluca’s volcanic activity on the karst development of the Cacahuamilpa area, Guerrero, Mexico

Cacahuamilpa Cave, along with several adjacent inactive systems and two lower active river caves, originated in response to Pleistocene volcanic processes associated with Nevado de Toluca, located approximately 50 km to the north. A catastrophic sector collapse of the volcanic edifice generated a large debris avalanche that evolved into the Pilcaya debris flow, which was channeled southward along the paleovalleys of the Chontacoatlán and San Jerónimo rivers. Prior to this event, these rivers converged to form the ancestral Amacuzac river, which incised the Cacahuamilpa limestone range via the Michapa canyon, establishing the regional base level for karst development. Subsequent remobilization of the volcanic deposits produced the Mogote debris flows, which overtopped the canyon and infilled the upper reaches of the Amacuzac valley, creating the Michapa plain and advancing approximately 20 km further downstream. The resultant depositional surface, convex in a direction transverse to the regional drainage, forced the two rivers to diverge toward the deposit’s periphery. The eastern drainage evolved into the San Jerónimo River, which continued to breach the limestone through the original canyon before skirting the western margin of the Mogote deposits across the Michapa plain. Conversely, the western drainage became the Chontacoatlán River, which carved a new course through the limestone massif via a preexisting low saddle. The increased hydraulic gradient across the limestone range promoted significant river infiltration into the karst aquifer. The combination of substantial discharge and a dense fracture network within the limestone facilitated the formation of extensive vadose and water-table–controlled conduits. A later rejuvenation of the Amacuzac river’s gradient resulted in the abandonment of the upper-level caves and the development of younger, currently active river caves at lower elevations. Continued volcanic activity at Nevado de Toluca triggered additional laharic episodes, the deposits of which were emplaced within these younger caves, where they remain preserved as inset terrace remnants. Similar volcanic-derived sediments have also been documented within Cacahuamilpa Cave.