Mad about Science: The Zanclean Flood

By Brenden Bobby
Reader Columnist

Tales of massive floods are a feature of virtually every religion in the history of humankind. The idea of a flood that can move mountains is a terrifying prospect, but is there any irrefutable evidence that this sort of thing has happened on Earth?

The Missoula floods were a major part of my fourth-grade curriculum. Local history and how massive geological events shaped our present are important to know. Lake Pend Oreille wouldn’t exist had it not been for an apocalyptic amount of water ripping through Montana, Idaho, Oregon and Washington on its way to the Pacific Coast.

During a 5,000-year period between 18,000 and 13,000 years ago, the world was in a major glaciation period commonly referred to as the Ice Age. These lower temperatures caused massive glaciers to form throughout the northern latitudes of Earth, particularly in North America. Some of these glaciers began to block major waterways by creating ice dams hundreds of feet high, particularly around modern-day Missoula, Mont. Water is extremely heavy, especially when it’s trying to move. Moving water also doesn’t freeze as quickly as stationary water, so these ice dams were only able to grow so much before giving way to the tremendous pressure of the liquid water behind them. When these dams broke, vast quantities of water were sent rushing toward the Pacific Ocean. Try to imagine a 400-foot-high wall of water ripping across the entire Pacific Northwest — it’s difficult to wrap your head around just how massive these events were.

That’s right, events being plural, because this happened multiple times over thousands of years. Even more wild, humans inhabited North America during this period and may have not only witnessed one or several of these flood events, but recorded them in story. 

Apocalyptic flood stories from the Klallam people of the Pacific Northwest describe events that are shockingly close to the Missoula floods. These floods struck with such force that they gouged away the earth to form a basin in what is now Lake Pend Oreille, forming the lake you recreate on and around to this day.

This is such a staggeringly huge event it’s almost impossible to accurately imagine. The ice dam would have stood 2,000 feet high — about as tall as the Shanghai Tower in China — holding back enough water to drown the entirety of North Idaho and western Montana.

But for as huge as the Missoula event was, it was akin to knocking over a bucket compared to the Zanclean flood.

Plate tectonics caused the European and African plates to collide 5.9 million years ago, effectively sealing the Strait of Gibraltar. This cut off the Mediterranean Sea from the Atlantic Ocean and caused a series of events that would change the ecology of northern Africa and southern Europe for hundreds of thousands of years.

Over the period of about 1,000 years, the Mediterranean dried up. We aren’t talking about water levels dropping a few feet — we’re talking the Mediterranean Sea dried up.

This created a completely new biome between the two continents that was a death trap for almost anything that dared explore this new land.

Due to the configuration of the Mediterranean and the relatively small amount of water that’s able to exchange with the Atlantic Ocean, it is naturally saltier than the Atlantic. Once the water evaporated, all that salt had to go somewhere, creating a colossal salt plain where very little could survive. Try to imagine the Great Salt Lake, but it’s 1,000 miles long and 400 miles wide.  That’s equivalent to a salt desert that would engulf a stretch of land north-to-south that includes Washington and Oregon, and west all the way to Minnesota.

Despite this massive salty death trap, some species of animals managed to cross between Europe and Africa. Hippopotamuses migrated from Africa to the Mediterranean, giving rise to the Cypriot dwarf hippo. Camels migrated into Turkey. Mice, voles and rabbits moved from Europe into northern Africa.

As wild as that sounds, the Mediterranean desert pales in comparison to the moment the Strait of Gibraltar finally gave way to the Atlantic Ocean. After 600,000 years of a world without the Mediterranean Sea, the immense pressure of water from the Atlantic Ocean finally caused the sealed up strait to burst open, sending an unfathomably huge volume of water roaring through the channel into a 3,300-foot-deep basin. It’s estimated that 3.5 billion cubic feet of water per second moved to refill the Mediterranean moving at speeds of up to 89 miles per hour. Meanwhile, 240 cubic miles of rock was carried from Western Europe to the eastern Mediterranean and deposited on the sea floor.

One of the most interesting elements of the story of the Zanclean flood and the Mediterranean is the human element. Humans wouldn’t evolve as we know them for almost 5 million years after those events. However, there were legends from the ancient Greeks recorded by Roman historian Pliny the Elder, in his work Historia Naturalis, that stated Hercules used his strength to carve out the Strait of Gibraltar and let the ocean flow into the Mediterranean.

Either the Greeks and Romans had some incredible foresight or, like the Klallam people, someone shared a story that was good enough to last 5 million years.

Stay curious, 7B.