Estimating volcanic plume heights from depositional clast size

摘要

Tephra deposits retain a considerable amount of information about the nature of volcanic eruptions, with plume height commonly inferred from maximum clast size measurements. However, current methods for inferring plume height from maximum clast size lose some of the accuracy in measurements made in the field and have limited application when trying to constrain the uncertainty in these parameters. Here a predictive numerical model is used to determine plume height from maximum clast size found in a deposit. Plume height is an essential parameter for inferring eruption magnitude as it is explicitly related to mass eruption rate. We investigate the effects of different atmospheric and wind profiles, allowing the input conditions to be location specific for each eruption. The use of a predictive model reduces the uncertainty in determining plume height as it retains the detail of measurements made in the field and incorporates the uncertainty in these measurements in the results, in the form of a probability distribution. We have applied this approach to fall deposits from the 1991 eruption of Pinatubo, one of the few Plinian eruptions in which the true height of the plume is well known. The predicted plume heights are in good agreement with those found from satellite measurements. This new approach provides a method for determining plume height from poorly preserved fall deposits, from which a limited amount of data can be sampled leading to large uncertainties in the field measurements.