ASSESSING TEPHRA FALLOUT HAZARDS IN CENTRAL AMERICA

Volcanic eruptions from volcanoes in Central America pose significant tephra fallout hazard to local populations due to accumulation of tephra and subsequent remobilization to form lahars. We present a computer code we have developed (TEPHRA2) to assist in the forecasting of tephra fallout. This code, based on the advection-diffusion equation, forecasts tephra fallout from eruptions of specific magnitude (e.g., column height, total erupted mass) and specific meteorological conditions. TEPHRA2 is linked to Monte Carlo simulations of eruptions for specific volcanoes and REANALYSIS models of meteorological conditions to forecast potential tephra fallout. The downhill simplex algorithm is used to estimate best-fit solutions of eruptions parameters, given the distribution of tephra fallout mapped for individual eruptions. TEPHRA2 is also used to assess eruption magnitude based on isopleth maps of “maximum” lithic size. TEPHRA2 is also used to map potential lahar source regions, either by linking to models of slope failure in saturated or unsaturated conditions, or through empirical correlation between tephra thickness and increased runoff. Examples are presented based on Concepcion and Cerro Negro volcanoes (Nicaragua), among others.