AshCalc–a new tool for the comparison of the exponential, power-law and Weibull models of tephra deposition

This paper presents a new tool, AshCalc, for the comparison of the three most commonly used models for the calculation of the bulk volume of volcanic tephra fall deposits: the exponential model, the power law model and the Weibull model. AshCalc provides a simple and intuitive tool to speed up the analysis of tephra deposits and compare and contrast the fits for each model. Two improvements in terms of computational performance are implemented in AshCalc for the estimation of the parameters for the Weibull model. The first is an analytic method for reducing the number of free parameters, whilst the second exaggerates the minima in parameter space, leading to a more robust solution. We show that AshCalc provides volume estimates in line with other previously published estimates and hence can be used with a high degree of confidence. We include the open source python code for Ashcalc with the intention that it can be used both as a stand-alone program and integrated into other python projects.