The formation of a sinkhole at the Napoleonville salt dome located near Bayou Corne in Assumption Parish, Louisiana, was preceded by an increase in seismicity, as observed 10 km away by a continuously recording broadband seismic sensor. The seismicity rate in the days prior to the sinkhole formation contained hundreds of long‐period events, some of which could be detected using a power detector (short‐term to long‐term energy ratio) tuned to the duration and frequency content of the seismicity. A characteristic of some of these events is a resonance near 0.4 Hz, which could be due to either an acoustic resonance within the brine‐filled cavity or possibly due to unsteady fluid flow through a crack. A more exhaustive catalog was obtained using some of the events detected by the power detector as templates in a correlation detector. The full pre‐sinkhole sequence of detections could offer lessons in remote monitoring of underground caverns.