The quantification of tephra fallouts can be affected by different parameters such as the quality of the deposit exposure and the calculation method. In this paper the effect of variability in the wind direction is investigated through the analysis of two eruptions from the Tungurahua volcano in Ecuador. The fluctuation in the wind direction was assessed using the alerts generated by the Washington VAAC (Volcanic Ash Advisory Center) and the actual fallout reports from local volunteers. Area densities (mass/area) of the tephra deposits were compiled by each co-author to create isomass maps. Empirical methods were used to calculate the total mass of the tephra fallouts. With this approach we were able to study the influence of the wind direction variability on the quantification of tephra fallouts under similar eruptive and sampling conditions. Our results indicate that, due to higher wind direction variability, the December 2012 eruption produced a non-elliptical complex deposit with a larger uncertainty on the calculated total mass value. The March 2013 eruption, on the other hand, occurred during a period of steady wind direction and left an almost elliptical deposit. The compilation of the data from the March eruption done by the co-authors demonstrates greater coherence and a less uncertainty in the final result. This study highlights that the choice of the empirical law to describe the fallout distribution must be adapted according to the map of the deposit.
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