Abstract

Preexisting topography played a major role in defining the distribution of the Xitle lava flows. Xitle is one of the youngest monogenetic volcanoes in southern Mexico City. The eruption was characterized by small ash emissions and nine pahoehoe and aa lava flows that covered 78.94 km2. 2 . In this paper, the paleo-topography of the Xitle volcano area was reconstructed to improve knowledge of the paleo-drainage and how it determined the trajectory of the lava flows and the formation of lava tubes. Deposits of pre-Xitle volcanoes (San Miguel Volcanic Complex, Ajusco, Cuilotepec, Coatzontle, Yololica and Malinale) were identified according to the morphology of the current relief. The contour lines of the present-day relief were modified to eliminate the topography left by the Xitle lava flows. The modified contour lines were then processed creating a raster surface from a TIN to obtain the digital elevation model of the paleo-relief. The distribution of the paleo-channels was defined by analyzing the accumulation and direction of flow in the paleo-relief. Lava flows were individually simulated in the paleo-relief with the probabilistic program Q-LavHA. Field observations and previous studies were integrated to define the parameters of lava flow simulations. Lava flows from the Xitle volcano covered the deposits of the pre-Xitle volcanoes except for the highest parts, such as ones from the Cuilotepec cone and the Ajusco hummocks. The lava flows also partially filled and modified some paleo river-channels (e.g. Magdalena), and completely filled others (e.g. Cuicuilco). The simulations show that the trajectory of lava flows and the existence and distribution of lava tubes are associated with variations in the effusion rate, arrangement of the paleo river-channels, morphology of the pre-Xitle deposits and the abrupt slope.