Earlier this month, New Jersey saw a “meteotsunami” hit its coast, according to the West Coast/Alaska Tsunami Warning Center.

The rare phenomenon struck the Jersey Shore on June 13, with Barnegat Light hit the hardest. There, “an approximately 6-foot wave knocked three people off the inlet jetty, injuring at least two of them,” according to USA Today’s report.

A more common tsunami is caused by earthquakes and other seismic activity underwater, and can result in waves reaching dozens of feet tall. The 2004 tsunami in the Indian Ocean killed over 230,000 people as it hit 14 countries.

The Jersey Shore’s smaller version from a couple weeks ago thankfully did not reach that level of damage, nor was it caused by the kind of underwater movements that are usually the cause of such waves. Instead, it seems that the weather conditions stirred the water just enough to produce a less-threatening but still massive event.

Talking to USA Today, Paul Whitmore, director of the Center, attributed the event to “a strong weather system that moved from across the eastern U.S. that day.” Such systems can cause tsunami-like conditions. And that particular day, New Jersey saw a low-end derecho that seems to have caused such an incident, although damage was minimal.

“It’s a complex process that generates these things,” Whitmore told the newspaper, “but the bottom line is you’re looking at a tsunami-like wave that generated from above instead of generated from below.”

The last time the East Coast saw a meteostunami was in Maine in 2008, which left some damage but no major injuries. Before that, you have to go back to 1992 when a similar event hit Daytona Beach, Florida and caused 75 injuries and damage to 36 vehicles. That wave was ten feet high.

According to Long Beach Township authorities in New Jersey, a father and son suffered injuries when the meteotsunami hit on June 13 and had to be airlifted for further medical attention. The father is still recovering.

While initial understanding seems to point to the weather as cause, scientists are still investigating.

“The first impulse was to see this as meteorologically driven,” Whitmore told Huffington Post, “but once a system gets over the [continental] shelf, we lose data. It makes it hard to confirm.”