From examination of natural events a proposal for risk mitigation of lahars by a cellular automata methodology: a case study for Vascún valley, Ecuador

Abstract. Lahars are erosive floods, mixtures of water and pyroclastic deposits, they look the biggest environmental disaster as number of fatalities in the volcanic areas. Security measures have been recently adopted in the threatened territories, by constructing retaining dams and embankments in key positions. Such solutions could involve a strong environmental impact for the works and the continuous accumulation of volcanic deposits, such that equilibrium conditions could lack far, triggering more disastrous events. An improved version of the Cellular Automaton model LLUNPIY for lahars simulations is presented. The growing frequency of lahars, maybe for the climatic change, in the Vascún Valley of Tungurahua Volcano, Ecuador has recently produced smaller and less dangerous events, sometimes favoured by the collapse of temporary ponds, generated by small landslides. An investigation is here performed in order to reproduce such situations in controlled way by the use of LLUNPIY simulations. Using precise field data, points are individuated where dams by backfills, easy to collapse, can produce momentary ponds; LLUNPIY simulations permit to project triggering of small lahars by minor rainfall events or to project in the case of larger rainfalls the anticipation of lahar detachment, avoiding simultaneous and dangerous confluence with other lahars.