Volcanoes produce sound during eruptions, even if inaudible to us. The May 22, 2021 eruption of Nyiragongo volcano in the Democratic Republic of Congo was closely monitored by analyzing inaudible sound waves, according to new research by KNMI and the European Centre for Geodynamics and Seismology in Luxembourg.
The Nyiragongo volcano has one of the largest lava lakes in the world. During an eruption in May 2021, this lava lake drained rapidly. The eruption had a huge impact on safety in the area, including the city of Goma (image 1). Although the process was not clearly visible everywhere on the surface, it was possible to track it through inaudible sound waves – infrasound.
Sound of a Draining Volcano
The sound was so intense that it could be measured even at a distance of over 800 kilometers
With special microphones placed less than 20 kilometers from the crater, the infrasound of the eruption was recorded in detail. The sound was so intense that it could also be measured at a distance of over 800 kilometers, at an infrasound station in Kenya that is part of the International Monitoring System (IMS). The IMS was established to verify the Comprehensive Nuclear-Test-Ban Treaty. Infrasound can detect above-ground nuclear tests.
In the infrasound, a drone lasting several hours was detectable (image 1). This tone can be explained by the formation of a cavity inside the volcano due to the draining of the lava lake. This created, similar to a guitar, a kind of resonating chamber. By simulating the sound signal in a model, researchers were able to reconstruct the draining of the lava lake in the crater.
Activity Along the Flanks
Besides the mentioned vibrations, the measured infrasound also provided information about the opening of fissures along the volcanos flank, from which new lava eruptions occurred. This activity happened simultaneously with the draining of the lava lake. In other words, one large volcanic system broke open in multiple places, and the entire scenario is reflected in the sound signal.
Infrasound for Volcano Monitoring
By measuring infrasound, we can better understand what a volcano is doing – and possibly warn and intervene earlier if danger threatens
The research around Nyiragongo shows that infrasound is an indispensable part of monitoring and surveillance of volcanoes, alongside seismic and satellite measurements. Infrasound can track processes that other instruments cannot always measure. By continuously measuring infrasound, we can better understand what a volcano is doing – and possibly warn and intervene earlier if danger threatens. In the Netherlands, infrasound from the Etna volcano on the Italian island of Sicily is regularly measurable.
Collaboration Between the Netherlands and Luxembourg
The research, recently published in the journal Nature Communications Earth & Environment, is a collaboration between KNMI and the European Centre for Geodynamics and Seismology in Luxembourg. These institutes have been working together since 2019 on the Comprehensive Nuclear-Test-Ban Treaty.
