A new method to identify the source vent location of tephra fall deposits: development and testing, and application to key Quaternary eruptions of Western North America

TL;DR

This paper introduces a new, flexible method combining gradient descent and semi-empirical models to accurately locate tephra source vents using deposit thickness and clast size data, even with sparse observations.

Contribution

It develops a novel approach that improves vent location estimation by integrating gradient descent with semi-empirical tephra models, and evaluates its robustness and uncertainty quantification.

Findings

Successfully applied to multiple tephra datasets with consistent results.

Estimates of vent locations and volumes align with previous studies.

Robustness of dispersal axis estimation with sparse data.

Abstract

A new method to identify the source vent location of tephra fall deposits based on thickness or maximum clast size measurements is presented in this work. It couples a first-order gradient descent method with either one of two commonly-used semi-empirical models of tephra thickness distribution. The method is successfully applied to three tephra thickness and one maximum clast size datasets of the North Mono and Fogo A tephra deposits. Randomly selected and localized subsets of these datasets are used as input to evaluate its performance in cases of sparse observations. The results suggest that estimating the dispersal axis is a more robust way to constrain the source vent location with sparse observations. Bootstrap aggregating and examining the surface of the cost function are proposed to characterize the uncertainty of the method. Distinctions between the two adopted semi-empirical models of tephra thickness distribution are discussed. Results from applying the method to thickness datasets of the Trego Hot Springs and Rockland tephras are consistent with previous studies, which also provide new estimates on their total volume. The method is then applied to a series of well-correlated tephra sub-units preserved within the Wilson Creek Formation to estimate their vent location and total volume. The simplicity and flexibility of the method make it a potentially useful and powerful tool for the study of tephra fall deposits of different characteristics.