A tidal wave is a common but misleading term for what scientists call a tsunami: a series of enormous ocean waves caused by underwater earthquakes, volcanic eruptions, or landslides. These waves can travel across entire oceans at very high speeds. In deep water they're barely noticeable, but as they approach shore, they slow down and pile up into walls of water that can reach heights of 100 feet or more, destroying much of what lies in their path.

Despite the name, tidal waves have nothing to do with tides. The confusion comes from how these waves behave at the coast: the ocean often pulls back dramatically before the wave strikes, like an extreme low tide, exposing the seafloor. This warning sign means a massive wave is coming within minutes.

People also use tidal wave figuratively to describe any overwhelming surge of something. A school might experience a tidal wave of excitement when snow cancels classes, or a politician might face a tidal wave of criticism after making an unpopular decision. In this sense, the phrase captures the idea of something powerful and unstoppable washing over everything in its path.

Throughout history, tsunamis have caused tremendous destruction in coastal communities around the world, which is why scientists now have warning systems to help people evacuate to safety when a tsunami is detected.