Wet vs. Dry the impact of water on infrasound eruption signals in crater lake volcanoes : April 2020 Anak Krakatau case study

Abstract

Infrasound, sound below the range of human hearing, is becoming recognized as a valuable addition to local volcano monitoring networks. Independent of cloud cover and time of day, infrasound provides a source of information for a wide range of surface activity. However, the presence of liquid water at the source has a significant impact on the style and amplitude of explosion signals produced, and hence on the interpretation. Understanding the impact of water on these signals is essential to understand the range of appropriate infrasound applications. In April, 2020, an eruptive sequence at Anak Krakatau, Indonesia, was captured on local infrasound sensors. This sequence included the drying out of the lake that had been present above the vent since the collapse of the island in December, 2018. This case study offers an opportunity to examine in detail the changes in close range signal characteristics within a system that exhibits both wet and dry conditions. Initial results indicate that the signal characteristics are significantly influenced by the presence of water. This project aims to understand how these changes influence the results of different processing methods used in infrasound monitoring. As infrasound measurements can be used to not only identify eruptions, but estimate eruption source parameters like plume height, it is important to understand how the presence of water might change the outcome of different monitoring methods. Therefore this has implications for monitoring networks including volcanoes with crater lakes, and the design of data processing methods.