Video of two manhole lids bouncing and rattling from wave pressure. On the shore of Lake Michigan, at Concordia University in Mequon, Wisconsin. During stormy weather on October 21, 2019.
The manholes are connected to storm sewers that flow into Lake Michigan a short distance away. As each big wave rolls in and breaks on the rock revetment, the wave forces water and air back up the storm sewer, and the increase in pressure causes the cast iron manhole lids (which usually weigh around 250 pounds or 115 kg) to shake, rattle and roll.
Original key: Concordia_2019_10_21_video_0747.mov