Structural and Lithological Control of a WATER Spring System on the Eastern Flank of Cofre De Perote Volcano, Veracruz, MEXICO

Cofre de Perote (4200 m a.s.l.) an extinct shield volcano, is the northern vent of a roughly NE-SW volcanic range with the active volcano Pico de Orizaba (5675 m a.s.l.) on it's southern edge. This feature constitutes a regional topographic barrier that condensates most of the moist air from the Gulf of Mexico. The eastern flank of the volcanic range is characterized by high precipitation rates, while on the western side, an intermountain lacustrine basin, a semiarid to arid environment prevails. Between the high lands and the basin plains of the Gulf of Mexico, the region presents a predominance of Pleistocene monogenetic volcanic vents and their associated pyroclastic deposits and lava flows. The basement of these young volcanic deposits is formed by older volcanic rocks and Mesozoic limestone. Two main systems of fracturing are present in the region: a NWW-SEE affecting the older rocks, and a NE-SW affecting the younger ones. The strong regional slope, the high geological control and the high precipitation values produce a complex net of water springs over an area of about 395 km2, where more than 60 springs were registered. 23 of them were selected in order to relate the location and the chemical and physical characteristics of the spring system to the stratigraphy and structural geology of the region. According to this, the springs have been classified in three groups: a) those associated with regional structures, b) those associated with lithological contacts, c) those associated with local fracturing. Because of it genesis and pathways, these springs are highly sensible to contamination, which have been detected because of the high levels of NO3.