Resumo

ACEVES QUESADA, Fernando; LEGORRETA PAULIN, Gabriel  e  ALVAREZ RUIZ, Yarummy. Geomorphologic mapping for the inventory of gravitational processes in the endorrheic basin of the La Ciénega gulch, Eastern flank of the Nevado de Toluca volcano. Bol. Soc. Geol. Mex [online]. 2014, vol.66, n.2, pp.329-342. ISSN 1405-3322.

The study area is an endorheic basin belonging to the La Ciénega River, on the eastern flank of the Nevado de Toluca volcano (NTV), and extends from the edge of the crater to the plain of the Valley of Toluca. La Cienega River flows onto the Alto Lerma plain, where the basin is closed by the Tépetl or Tenango andesitic lava flows. The alluvial fan at the mouth of the La Cienega River is composed of ancient debris flows and lahar deposits. An urban settlement of 2500 inhabitants called Santa Cruz Pueblo Nuevo (2880 masl), municipality of Tenango del Valle, State of Mexico, is located here. On June 24, 1940, a torrential rain triggered a large debris flow that destroyed the locality. The town had to be rebuilt and was thus named Pueblo Nuevo (new town). In spite of this disaster, the town of Santa Cruz and the current Tenango-Ixtapan de la Sal highway are on the fan, thereby endangering the inhabitants and infrastructure. The NTV is a stratovolcano that has erupted at least eighteen times during the past 60000 years. Vulcanian, plinian and merapi type eruptions have left thick deposits of diverse pyroclastic materials. The geomorphologic survey shows that the basin has developed on a slope of pyroclastic material composed of block and ash flow deposits (with greyish and reddish dacitic lithics, of sizes ranging from 2.5 cm to 2.5 m in diameter), debris avalanche deposits, lahar deposits, surges, ash flows and pumice falls (fragments from 1 to 10 cm diameter), which are materials that are only slightly cohesive and easily eroded. At the river head a network of canyons between 50 and 150 m deep has developed. The middle and lower parts of the basin have developed on the volcanic foothills, with ravines from 25 to 150 m depth, in which creep processes favor the development of shallow (< 2 m) and deep landslides (> 2 m). Rock falls into the valleys contribute to the formation of debris flows, and supply material for the alluvial fan formed at the mouth of the La Cienega River. A geomorphological survey and a preliminary landslide inventory was conducted, as part of the landslide study that was carried out in the basin of the La Ciénega River. The geomorphological survey included five morphometric maps (hypsometric, internal relief, vertical dissection, slopes, and potential erosion); five transversal profiles over the course of the river, and geomorphologic and geologic maps.

Palavras-chave : geomorphological cartography; gravitational processes; geographical information systems; Nevado de Toluca volcano; La Ciénega River; México.