Geology topics

Sonja A. Behnke

Publications and source records attributed to Sonja A. Behnke.

4 recordsLinked to original sources

USGS2025

Monitoring lightning and electrification in volcanic plumes

Detection of the electrical discharges and, more fundamentally, the electrification from volcanic plumes is an emerging capability for volcano monitoring. In addition to being able to detect an explosive eruption, such measurements also provide insight into volcanic processes. Volcanic lightning monitoring can be achieved through varying levels of complexity. At the lowest complexity, an observatory can use low-cost global lightning data sets for eruption detection and characterization, while at the highest complexity local lightning sensors can be installed to improve the level of observational detail and response times. This chapter provides background about volcanic lightning and plume electrification, information concerning the relevant instrumentation to detect lightning and electrified plumes, examples of how lightning can be used to understand eruptive processes, and a guide to implementing volcanic lightning detection into a monitoring scheme.

Book chapter↗

USGS2023

Lightning rings and gravity waves: Insights into the giant eruption plumefrom Tonga’s Hunga Volcano on 15 January 2022

On 15 January 2022, Hunga Volcano in Tonga produced the most violent eruption in the modern satellite era, sending a water-rich plume at least 58 km high. Using a combination of satellite- and ground-based sensors, we investigate the astonishing rate of volcanic lightning (>2,600 flashes min −1 ) and what it reveals about the dynamics of the submarine eruption. In map view, lightning locations form radially expanding rings. We show that the initial lightning ring is co-located with an internal gravity wave traveling >80 m s −1 in the stratospheric umbrella cloud. Buoyant oscillations of the plume's overshooting top generated the gravity waves, which enhanced turbulent particle interactions and triggered high-current electrical discharges at unusually high altitudes. Our analysis attributes the intense lightning activity to an exceptional mass eruption rate (>5 × 10 9 kg s −1 ), rapidly expanding umbrella cloud, and entrainment of abundant seawater vaporized from magma-water interaction at the submarine vent.

Hunga Volcano↗

USGS2022

Discriminating types of volcanic electrical activity: Toward an eruption detection algorithm

We present a method for classification of the two distinct types of electrical activity that occur during an explosive volcanic eruption: vent discharges and lightning. Vent discharges occur at the onset of an explosion and create a distinctive radio frequency signature called continual radio frequency. Seconds to minutes after the onset of the eruption, lightning begins to occur throughout the eruption column. We use logistic regression to classify a radio frequency impulse as being part of either a lightning flash or a period of continual radio frequency. The classifier uses the number of peaks in the amplitude envelope from 1 ms windows before and after the impulsive very high frequency waveform, with an average accuracy of 97.9%. We propose that this method could be used in an algorithm to determine when explosive eruptions occurred by identification of the distinctive signatures of vent discharges and lightning.

Geophysical Research Letters↗

USGS2021

Impulsive volcanic plumes generate volcanic lightning and vent discharges: A statistical analysis of Sakurajima volcano in 2015

The origin of electrical activity accompanying volcanic ash plumes is an area of heightened interest in volcanology. However, it is unclear how intense an eruption needs to be to produce lightning flashes as opposed to “vent discharges,” which represent the smallest scale of electrical activity. This study targets 97 carefully monitored plumes <3 km high from Sakurajima volcano in Japan, from June 1 to 7, 2015. We use multiparametric measurements from sensors including a nine-station lightning mapping array and an infrared camera to characterize plume ascent. Findings demonstrate that the impulsive, high velocity plumes (>55 m/s) were most likely to create vent discharges, whereas lightning flashes occurred in plumes with high volume flux. We identified conditions where volcanic lightning occurred without detectable vent discharges, highlighting their independent source mechanisms. Our results imply that plume dynamics govern the charging for volcanic lightning, while the characteristics of the source explosion control vent discharges.

Sakurajima volcano↗