Bubbles: A matter of life and death

The growing use of hydroacoustics to study magmatic degassing underwater is providing increasingly powerful insights in topics as varied hazard monitoring and microbial evolution. This talk will discuss the use of marine acoustics to study magmatic degassing and present two case studies, 1) Dziani Lake (Mayotte) a Precambrian analogue where variations in magmatic degassing may be driving microbial adaptation , and 2) Lake Kivu (Rwanda) where deadly limnic eruptions may be triggered by newly discovered gas blowouts.

 

Hydrophones record the sound emitted by gas bubbles at the moment of their release into the water column. The frequency and power of these signals tells us about their number and size. By applying Passive Acoustic Flux Inversion techniques, bubble oscillation spectra can be inverted to passively quantify gas flux continuously,  regardless of water quality or depth. This approach enables long-term monitoring of degassing dynamics that are inaccessible using traditional geochemical or visual methods.

Dziani Dzaha Lake undergoes persistent magmatic degassing and is considered one of the best modern analogues for Precambrian environments. A better understanding of what drives adaption in the microbial population of Dziani provides a better understanding of what drove Precambrian evolution. A month long observation reveals strong temporal variability in gas flux, with rapid increases potentially preceding local seismic activity. These observations provide the first quantitative constraints on magmatic gas input to the lake and may suggest a tentative link between volcanic activity and early life.

At Lake Kivu, a hydrophone deployed during the 2021 Nyiragongo dyke intrusion provided the first direct acoustic observations of lakebed degassing. Analysis reveals highly variable degassing behaviour, including pulsed bubble releases, long-period signals associated with subsurface gas migration, and previously undocumented explosive gas blowout events on the lakebed. These high-energy events have the potential to trigger limnic eruption but were not detected by the regional land-based seismic network, highlighting critical gaps in current monitoring strategies. Although no limnic eruption was triggered, the observations demonstrate that potentially hazardous degassing processes can occur silently and episodically, challenging assumptions of steady gas input used in existing limnic hazard forecasts.

Together, these case studies demonstrate the growing potential of hydroacoustics to study magamtic degassing and will hopefully inspire future studies incorporating the use of hydrophones to study magmatic degassing.