Ionospheric Disturbances

https://earth-planets-space.springeropen.com/articles/10.1186/s40623-022-01619-0

Japan monioring ionospheric disturbsnces preceeding volcanic eruptions..  They have set up an extensive monitoring system since Fukushima. 

The key point is 2 sets of waves were measured.  The first set preceeded the acoustic waves.