Infragravity Waves
Here on the coast, we're used to seeing wind-driven waves breaking as they come ashore during a storm, but occasionally there can be a wave that has such a long wavelength that it doesn't break; it can resemble a tsunami when it rolls ashore — even though it isn't associated with any geologic event.
On November 8, 2013, during Typhoon Haiyan, a super-long "infragravity" wave was caught on video in Hernani, in Eastern Samar, Philippines. The following video illustrates the reasoning behind mandatory evacuations. At least 6,300 people died, mostly due to the storm surge, making it the deadliest typhoon in modern Philippines history. It was only by the grace of God that the person making this video survived.
The wave was powerful enough to move a 180-ton boulder on the beach.
/fl