Silent VLPs at Stromboli volcano

At Stromboli Volcano, Italy, very long period (VLP) seismic signals and strombolian eruptions have been attributed to the unsteady flow of gas slugs through the shallow plumbing system followed by explosive slug bursting at a free surface. In data from a 2018 seismo-acoustic deployment, ~92% of events in two main VLP multiplets do not coincide in time with impulsive infrasonic signals (the expected signal of explosive slug bursting); we term these `silent VLPs'. The lack of infrasonically-detected explosions relative to

repeating VLPs does not support the commonly-invoked `gas slug' model. We propose that VLPs may be generated when gas bubbles move into a weak semi-solid plug in the uppermost portion of the conduit. The plug then acts as a mechanical filter in which pathways vary and guide or trap ascending gas slugs, allowing for passive (silent) gas release and explosive escape mechanisms decoupled in time from VLPs.

McKee et al., AGU Fall Meeting (2019)

McKee et al., GRL (2022)

Remote Characterization of Raikoke and Ulawun Eruptions

2019 Eruption of Raikoke volcano, Kuril Islands captured by the International Space Station

Our work is now published in a pair of papers McKee et al., 2021 (a-Raikoke and b-Ulawun)

2019 Eruption of Ulawun volcano, Papua New Guinea. Photograph taken by Craig Powell.

The 2019 program of the Cooperative Institute for Dynamic Earth Research (CIDER) was organized on the notion that multidisciplinary teams can advance understanding of volcanic processes. Fortuitously, two of the largest explosive volcanic eruptions of the past decade occurred during the program, at Raikoke, Kuril Islands and Ulawun, Papua New Guinea, providing an opportunity to apply this notion in the immediate aftermath of these events. As a CIDER work group, we integrated data from satellites (including Sentinel-2, TROPOMI, MODIS, Himawari-8), the International Monitoring System infrasound network, and globally-detected lightning (e.g., GLD360, WWLLN) with information from local authorities and social media to improve understanding of the pre-, syn- and post- eruptive behavior of these volcanoes.

Ground-coupled Airwave Backazimuth Determination (GCABAD)

The final project of my PhD was the development of a minimalist infrasonic signal detection and characterization technique requiring just one microphone and one three-component seismometer. This technique could be advantageous in situations where resources are limited. The development of this signal detection and characterization technique for ground-coupled airwaves using a nearly collocated seismometer and microphone was feasible because of groundwork laid out in Ichihara et al. [2012] and Matoza and Fee [2014]. This work was a poster presentation at the AGU Fall Meeting 2016 (Poster) and was presented at the IAVCEI 2017 Scientific Assembly in August. Details of this method are published in the Journal of Geophysical Research [McKee et al., 2018].

Stromboli Field Campaign

May 2018 Field Campaign

Here are some pictures of two great weeks at Stromboli with an amazing field team. We deployed seismometers, microphones, FLIR, FTIR, and a gravimeter.

2018 Seismo-acoustic campaign data available through the IRIS DMC: https://doi.org/10.7914/SN/YI_2018

Fumarolic jet noise at Aso volcano, Japan

This work is an in-depth investigation of a specific acoustic signal, volcanic jet noise, also referred to as volcanic jetting or simply, jet noise. Volcanoes generate jet noise at a variety of scales, from low-level gas jetting to violent subplinian-plinian volcanic jets. Research on jet noise produced by jet engines and rockets has shown there is a relationship between jet noise and the jet's parameters (i.e. jet velocity, temperature, nozzle diameter, etc.) that continues to evolve with increased understanding. Jets have been observed to be self-similar; in other words, they scale. This scaling implies that lessons learned in human-made jet noise studies could be applied to volcanic jets. The challenge lies in that volcanoes are not jet engines with smooth surfaces, easily measurable features, and comparatively constant shape; rather they are dynamic and complex, with varying surrounding topography and flow features. This varied nature is what makes them not only fascinating but also dangerous to the local populous and global air traffic. Although the length scales of laboratory and volcanic jets are vastly

different, the acoustic features should scale similarly. This suggests that studying smaller-scale volcanic jets, such as from gas jetting fumaroles, is useful. A fumarole is a vent in an active volcanic environment that issues steam and other volatiles (i.e. carbon dioxide, sulfur dioxide, etc.) at temperatures greater that 100°C. Here is an example from Mt. Griggs, Alaska. Fumaroles are more accessible and easier to characterize, and should scale to large, less frequent and more hazardous volcanic jets with plumes that reach 10 to 30+ km in the atmosphere. In the past fumaroles have been recorded but not investigated in depth. Our aim for this work was to understand fumarole acoustics and its relation to degassing to better understand volcanic jetting and its relationship to other eruptive activity. To achieve this we characterized the acoustic signal from a gas-jetting fumarole at Aso volcano, Japan, investigated the path effects and estimated the volatile flux using the acoustic data, thermal infrared images and published gas composition data. More details can be found in the paper McKee et al. (2017).

Semblance Source Location at Sakurajima

An important step in advancing the science and application of volcano infrasound is improved source location and characterization. Semblance is a commonly used technique for determining both seismic and infrasound source locations at volcanoes. The method uses a forward grid search in which each unique sensor pair is time-shifted for each grid node, and then cross-correlated to determine which time-shift and respective node provides the best fit. This work evaluated the infrasonic source location at Sakurajima Volcano, Japan using the semblance method on data collected in July 2013. The activity at Sakurajima Volcano consists of strombolian to vulcanian style explosions. Five sensors were deployed in a network configuration around Sakurajima with vent to sensor distances ranging from 2.3 to 6.2 km and a maximum vertical relief across the network of 356 m. All sensors were deployed at elevations below that of the active vent. We investigated semblance in 2D and 3D to assess the necessity of considering 3D sensor and vent locations. Semblance-derived

infrasonic source locations showed a clear offset of ~420 m from the actual vent. To determine the cause of the source location offset we evaluated semblance in multiple frequency bands, as diffraction around topography should be more severe at high frequencies. We also incorporated influences on sound speed such as diurnal temperature variations and wind speed, and tracked changes in the travel time associated with peak semblance over the dataset period. The source location offset is likely the result of significant local topography as the volcanic edifice lies between the vent and the sensor for two stations. This is evidenced by differences in frequency content across the network and consistent travel-time differences. Semblance can also be used to track and characterize volcanic activity, as periods of high semblance correspond to the eruption of ash and gas. Further details of this work can be found in McKee et al. [2014] or the poster below, which was presented at Cities on Volcanoes 8, Yogyakarta, Indonesia.