What Is the Largest Waterfall Ever Known on Earth?

Dry Falls in Washington State is the largest waterfall ever known on Earth — a 400-foot-tall, 3.5-mile-wide cliff that once thundered with more water than all of Earth’s rivers combined, before going silent thousands of years ago.

A Waterfall Bigger Than Anything Alive Today

Dry Falls sits in the Grand Coulee region of Washington State, and its scale is almost impossible to process. At 3.5 miles wide and 400 feet tall, it is five times wider than Niagara Falls. Standing at the rim today, the cliff curves around you like a vast amphitheater — magnificent, silent, and completely dry. It hasn’t carried a single drop of water for roughly 13,000 years.

The Ice Age Flood That Created It

During the last Ice Age, a glacial ice dam in present-day Montana held back an inland sea called Glacial Lake Missoula — roughly 500 cubic miles of water, about half the volume of Lake Michigan. When that dam catastrophically failed, it released one of the most violent floods in Earth’s geological history.

The water didn’t trickle. It surged across the Pacific Northwest at 65 miles per hour, carving the scarred landscape now known as the Channeled Scablands — ripping away topsoil, slicing through basalt bedrock, and pouring over the cliff at Dry Falls in a torrent so massive that the roar would have been audible hundreds of miles away. This likely happened not just once, but dozens of times as the ice dam repeatedly formed and failed over thousands of years.

J Harlen Bretz and the Flood Nobody Believed

In 1923, a geologist named J Harlen Bretz looked at the Channeled Scablands — the stripped rock, the giant ripple marks, the coulees — and proposed something radical: a single catastrophic flood had created all of it. The geological establishment was not impressed. The dominant scientific thinking of the era held that landscapes formed slowly and gradually. The idea of a sudden, cataclysmic flood sounded unscientific — even biblical — and Bretz was widely ridiculed.

He held his ground for nearly four decades. By the 1960s, the evidence had become impossible to dismiss. Satellite imagery, field mapping, and the discovery of Glacial Lake Missoula’s remnants confirmed everything Bretz had argued. In 1979, at 96 years old, he received the Penrose Medal — geology’s highest honor. His acceptance letter contained three words: “All my enemies are dead.”

What Dry Falls Taught Us About Mars

The story didn’t end on Earth. When NASA scientists began analyzing imagery of Mars, they noticed enormous channels carved into the Martian surface — formations that looked strikingly similar to the Channeled Scablands. Geologists used Dry Falls and the surrounding landscape as a physical reference point to interpret those Martian features, concluding that ancient catastrophic floods had once reshaped Mars as well.

A dry cliff in central Washington became a key to reading another planet’s past.

A Geological Heritage Site of Global Importance

In 2022, the International Union of Geological Sciences (IUGS) named Dry Falls one of the first 100 Geological Heritage Sites on Earth — a designation recognizing locations of exceptional scientific value to humanity’s understanding of the planet. Few sites on that list can claim to have also shaped our understanding of another world.

The waterfall is gone. What remains is the skeleton of the most powerful cascade ever documented — and one of the most consequential geological discoveries in modern science.