Abstract

Estimating tephra fall volumes is critical for assessing the impacts of explosive eruptions calculating eruption source parameters (ESPs). Estimates are subject to uncertainties that span from measuring deposit thicknesses to the different volume integration models implemented. In this sense, the number of field control points (FCPs) may produce variable volume outputs. In this contribution, we use a high-resolution dataset consisting of 270 FCPs to assess the 2011-2012 Puyehue-Cordón Caulle sub-Plinian tephra volume (previously estimated at 0.5–1.5 km3). We used a suite of randomly selected sub-datasets of FCPs ranging from 10 to 250. Hand-drawn isopachs were then integrated by the exponential and Weibull methods, with the goal of determining a minimum sample size to obtain volume estimation with little or no variation compared to the full dataset. Obtained bulk volumes range from 0.91 to 22.7 km3. However, the estimates converge to 1.15 ± 0.05 km3 when all the dataset is used, which is similar to results using c. 400 FCPs in the literature. Therefore, datasets of 89 and 60 samples for exponential and Weibull models, respectively, yield tephra fall volume estimates similar to considering the whole dataset. Notably, a small number of FCPs (50-70) generally produces volume overestimation to ≥30 % using the exponential method. Increasing FCPs yield more accurate isopach maps, while data distribution is important for volume uncertainty as medial observations account for larger volumes than the distal ones. These results provide new insights on the uncertainties associated with interpreting ESPs from tephra fall deposits.