Lahar deposits in the Cutio river subcatchment; Pico de Tancítaro volcano, Michoacán, Mexico

Abstract

Lahars originated from inactive volcanoes can cause economic damage and loss of lives in their surroundings without any warning if a record of past events is not available. These phenomena have been studied in several volcanic regions in Mexico; however, in most of those cases, there is a lack of long-term registry of their magnitude and frequency. In this work, we evaluate the features of lahar deposits and other volcaniclastic deposits (historic and modern) found in the Cutio river subcatchment, located in the northwestern flank of Pico de Tancítaro volcano, whose natural drainage crosses the localities of Peribán de Ramos and Corona, in the state of Michoacán. Within this subcatchment, a hyperconcentrated flow took place on September 23, 2018, after 58 mm of accumulated rainfall in 2 hr, which caused the overspill of Cutio river. This event affected the urbanized zone of Peribán and deeply eroded the riverbanks and riverbed of Cutio, leaving ancient deposits exposed along the walls of the river, which were analyzed in this work. To characterize these deposits, we conducted stratigraphic and granulometric analyses, ¹⁴C dating, and X-Ray diffraction analysis. From these, we identify four units classified according to their granulometric distribution as cohesive debris flows, whose origin can be associated to discrete flank failures from the western flank of the Pico de Tancítaro volcano. We also recognized a horizon interstratified with these deposits, classified as a pyroclastic fallout of scoria and ash, dated at ca. 20970 yr B.C. by ¹⁴C. Apart from these past units, we also identified deposits inside and outside of Cutio riverbed that were classified as hyperconcentrated flows associated with the flood event of September 2018. The data here presented bring to light new evidence about the historic record of lahars at Pico de Tancítaro volcano, including hyperconcentrated and debris flows from overflowing of the Cutio River, and also cohesive debris flows derived from the collapse of hydrothermally altered portion of the edifice. In case that this type of activity occurs in the future, it might have catastrophic consequences for the surrounding areas. Although the Pico de Tancítaro volcano is considered inactive, our results indicate that a detailed lahar hazard evaluation is needed to mitigate their impact in the urban and agricultural zones susceptible to be flooded, including the localities of Peribán de Ramos and Corona, Michoacán.