What the heck is that? From the article linked below –
CLICK TO ANIMATE! Cross-section through the Old Faithful area showing the location of hydrothermal tremor with depth over time, spanning an Old Faithful eruption cycle. The triangles denote the seismic stations, gray lines are the back-tracked directions from the seismic stations to the tremor source, warm colors indicate the most likely location of the tremor source, and the star marks the location of Old Faithful. Taken from an article by Wu et al., 2019, in Geophysical Research Letters, doi: 10.1029/2018GL081771.
From the USGS comes a damned interesting new article covering an update of what the best guesses are about the underground plumbing that makes Old Faithful so…faithful. Read the full piece here.