Hey there! Imagine standing in a dry, rocky place in eastern Washington, looking at a waterfall. It might seem like an ordinary waterfall, but it holds a secret about one of the biggest floods ever known on Earth. This flood was so massive that it’s hard to even imagine. Let’s dive into this fascinating story!
Our journey begins in a beautiful river valley in Missoula, Montana. Thousands of years ago, at the end of the last Ice Age, this valley was home to a gigantic lake called Glacial Lake Missoula. This lake was formed when a huge ice sheet blocked a river, creating a natural dam. The lake was so big that it held more water than Lake Ontario and Lake Erie combined!
But here’s the catch: ice floats in water. Over time, the pressure from the water behind the ice dam became too much. Eventually, the ice dam broke, unleashing a flood of water that was more powerful than all the rivers on Earth combined. This sudden release of water is known as a “jökulhlaup,” and it changed the landscape in just a few days.
The floodwaters raced across the land at incredible speeds, carving deep channels and canyons into the earth. This region is now known as the Channeled Scablands. One of the most impressive sights is Dry Falls, which was once the largest waterfall in the world during the flood. The water was so powerful that it even moved giant boulders across the landscape.
Normally, we think of erosion as a slow process, but this flood reshaped the land almost instantly. How? The area is made of a special type of rock called basalt, which was already cracked and ready to be swept away by the floodwaters. This rock was formed millions of years earlier by volcanic eruptions.
What’s even more astonishing is that this wasn’t a one-time event. Scientists believe that the ice dam melted and refroze up to 25 times, causing repeated floods over several centuries. Each flood left its mark on the landscape, creating new features and changing the course of rivers.
When geologist J. Harlen Bretz first suggested the idea of these massive floods in the 1920s, many people thought he was crazy. At the time, scientists believed that Earth’s features were shaped slowly over time. But the Missoula floods showed that sometimes, rapid and violent events can have a huge impact on the planet.
The story of the Missoula floods teaches us to look closely at the world around us. The Earth has many stories to tell, written in its rocks and landscapes. By studying these stories, we can learn more about our planet’s history and the forces that have shaped it.
Speaking of shaping the planet, did you know that humans have been affecting the Earth’s climate for over a century? Climeworks is a company that helps fight climate change by removing carbon dioxide from the air. They use a technology called direct air capture to permanently store CO2 underground, turning it into stone. This helps reduce the amount of CO2 in the atmosphere and combat global warming.
Climeworks’ CO2 capture plants are powered by renewable energy, making them an eco-friendly solution. You can even subscribe to a plan to help remove CO2 in your name. It’s a great way to make a positive impact on the environment!
So, keep exploring, stay curious, and remember that the Earth has many amazing stories waiting to be discovered!
Imagine you are a geologist studying the ancient Glacial Lake Missoula. Use materials like clay, water, and small rocks to create a model of the lake and the ice dam. Observe what happens when the “ice dam” breaks and discuss how this relates to the Missoula Floods.
Use a map of eastern Washington to identify and mark the Channeled Scablands. Research and label key features such as Dry Falls and other landmarks formed by the Missoula Floods. Discuss how these features were created by the floodwaters.
Conduct an experiment to simulate erosion using small basalt rocks and water. Observe how water affects the rocks over time. Discuss how the rapid erosion during the Missoula Floods differs from normal erosion processes.
Imagine you are J. Harlen Bretz presenting your theory of the Missoula Floods to skeptical scientists in the 1920s. Prepare a short presentation explaining your evidence and how these floods shaped the landscape. Discuss how scientific ideas can change over time.
Research Climeworks and their direct air capture technology. Create a poster or presentation explaining how this technology helps combat climate change. Discuss how understanding past events like the Missoula Floods can inform our approach to current environmental challenges.
Thank you to Climeworks for supporting PBS. Hey, smart people, Joe here. I’m in the scablands of eastern Washington right now, and that’s a waterfall behind me. It’s a pretty nice waterfall, but as waterfalls go, it’s actually pretty average. Its height and the volume of water that falls over its face don’t rank anywhere near the top 10. However, this waterfall does hold one important record among all waterfalls. It was created in what is perhaps the largest flood to ever happen on planet Earth, at least that we know of. Whatever you’re imagining as this flood, you need to think bigger—much, much bigger.
Because the flood that created this and the entire landscape around us is bigger than anything that could happen on the planet today, by a long shot. Across what is today a dry and arid landscape, there are clues of an epic flood hidden in rocky scars and strange landforms if you know how to read them. The pieces of this mystery are hard to make sense of on their own, but together they tell a story that’s almost impossible to believe. In fact, it took decades for scientists to finally accept that these cataclysmic events really did happen. This discovery completely changed science, forcing geologists to rethink their ideas about the powerful forces and events that have shaped the Earth throughout deep time.
Our story begins hundreds of miles to the east in a beautiful river valley where today we find the town of Missoula, Montana. This is the Glacial Lake Missoula high water mark, which marks the highest level that Glacial Lake Missoula reached in Missoula Valley. This would have been the shore of a giant glacial-fed lake. If we had stood in this spot 15,000 years ago, we would have found ourselves on the shore of an immense lake. At the end of the last Ice Age, the valley below us sat beneath 300 meters of peaceful blue water.
As far as you can see would have been basically underwater, except for where we’re standing and the tops of some of these taller mountains. These would have just been little pointy islands in the lake. It was called Lake Missoula, a freshwater inland sea, more than 600 meters deep at its deepest point, holding more water than Lake Ontario and Lake Erie combined. But why was there a lake here? About the past million years, massive ice sheets advanced and retreated across the Northern Hemisphere during natural cycles of climate change. During the last Ice Age, an ice sheet stretched unbroken from Alaska to today’s US-Canada border. One little finger of that ice sheet sat here at the end of this river valley.
That massive mountain of ice would have been right here. You need to picture something more like a massive wall of ice, 2,000 feet tall, 30 miles wide at its widest, blocking the river and forming Glacial Lake Missoula. Just like a stopper filling a bathtub, river water, rain, and melted snow backed up behind this ice dam for centuries, forming a lake covering nearly 8,000 square kilometers. But there’s just one problem: ice floats in water. A few leaks began to form in the ice dam, and with the weight of thousands of cubic kilometers of water pushing against it, one day… it catastrophically failed. The explosion, the sound of it, probably would have carried throughout the entire northwest. It drained probably in a couple of days.
A glacial lake twice the size of Rhode Island emptied in just a couple of days, and the torrent of water escaping the broken ice dam was equivalent to more than 10 times the flow from all the rivers on the planet. This kind of sudden glacial outburst is called a jökulhlaup. It’s almost impossible to put into scale the unimaginable power of these floodwaters, but right behind me, we can see proof of them. If you’ve ever seen those little ripples that form in the sand at the bottom of a little stream, well, there are ripples at the bottom of this valley caused by the floodwaters.
As thousands of cubic kilometers of water emptied out of this giant bathtub, flowing more than 120 kilometers per hour, it set off the worst and most destructive flood that we know of in Earth’s history. We think of erosion as something happening slowly over eons, but these Ice Age floods cataclysmically reshaped the landscape in just a matter of days. Water swept the land clean of topsoil, gravel, and sand. It even ripped away bedrock in some places. From above, we can see the scars left by this violent flood, branching channels and coulees carved deep into the Earth. They give this region its nickname, the Channeled Scablands.
And there’s nowhere that demonstrates the unimaginable scale and power of these floodwaters better than here, Dry Falls. About 50 kilometers south of the Grand Coulee Dam, we find what looks today like a deep, broad canyon, slowly carved into the Earth over eons. But that’s not what happened here. Everything you see was carved almost instantly by the violent floodwaters from Lake Missoula. During the floods, this was the largest waterfall in the world, five times the width of Niagara Falls. The water was more than 30 meters deep as it rushed over the edge, ripping away rock from its 120-meter face and carrying it downstream.
Elsewhere, powerful flood surges cut deep vertical canyons and cataract cliffs in just days. The raging waters were powerful enough to redirect entire rivers. The ancient path of this river flowed west through the Washtucna Coulee. But during the floods, the river overflowed its banks, raged south, and cut this new waterfall. All across the scablands, raging whirlpools of floodwater carved potholes and craters into the bedrock. The floods were so powerful they carried giant granite boulders embedded in icebergs, dropping them hundreds of kilometers from the mountains where they originated.
But there’s another mystery to solve. When we think about eroding rocks, that seems like something that should take thousands, millions of years even. How did a flood that only lasted a couple of days do so much damage to this landscape? Well, that’s because it’s made of a very special kind of rock that came from another kind of flood millions of years before the Ice Age floods. It was a flood of lava. All across this area, massive eruptions happened that laid down lava 2,000 feet thick in some places and that cooled into basalt.
As that lava cooled over decades, even centuries, it contracted and fractured along these amazing geometric faces. When that flood came through here, these columns were already pre-broken, ready to be swept away. So, thousands of years ago, a wall of ice was violently destroyed, emptying 20 million cubic kilometers of water per hour into eastern Washington, scouring and reshaping the surface of the Earth, causing eons of erosion in mere days.
And eventually emptying out into the Pacific Ocean, where huge amounts of sediment and rock from Montana, Idaho, and Washington can still be found today. And what’s crazy is this didn’t just happen once. It’s now thought that this ice dam repeatedly melted and refroze as many as 25 times over several centuries, each time devastating the land with epic floods. We can see evidence that Lake Missoula repeatedly filled and emptied in the so-called strand-lines marking the hills around the town, each an ancient shoreline of this Ice Age lake.
These violent events all happened surprisingly recently in human history. Archaeological evidence tells us that humans had already crossed into North America by the time of the floods. The creation stories told by the Nez Perce and Palouse Indian tribes even contain similar flood elements. We know there were animals and humans in the area during this time.
When geologist J. Harlen Bretz first proposed the idea of the Missoula floods in the 1920s, people thought he was nuts. At the time, geologists just didn’t think that large catastrophic events like this really happened. Instead, everyone figured that Earth’s geologic formations were carved only by the same slow, gradual processes still happening today like rivers, glaciers, and weather. The old slow and steady idea called uniformitarianism now stood alongside a new idea called catastrophism, where rapid and violent events could sometimes shape Earth’s geology in ways that slower processes couldn’t explain.
The Ice Age floods of Lake Missoula changed the face of our planet in violent and dramatic ways, but they also changed science. Our planet’s shapes and scars tell stories written in time and stone if you know how to read them. So listen to the Earth, keep your eyes open, and stay curious. Thank you, Kallie, for hiking us up here. And if you want to be taken on more great prehistoric adventures, go check out “PBS Eons.”
And thank you to Climeworks for supporting PBS. Did you know that for over a hundred years, humans have been extracting carbon from the Earth, releasing excess carbon dioxide into the air and instigating climate change? Climeworks enables us to fight climate change by permanently removing CO2 from the air. They use a technology called direct air capture that removes unavoidable and historic CO2 emissions from the air. The captured CO2 is then stored by Carbfix, who turns CO2 permanently into stone underground where it can no longer contribute to global warming.
And what’s really great is their CO2 capture plants are powered by renewable energy only. You can subscribe to a monthly or yearly plan that will help you remove CO2 in your name. Just head to actnow.climeworks.com/besmart and learn more about removing CO2 from the air.
Floods – Floods are natural events where an area that is usually dry becomes submerged in water, often due to heavy rain or overflowing rivers. – Example sentence: The floods caused by the heavy rains damaged many homes and roads in the valley.
Lake – A lake is a large body of water surrounded by land, usually filled with fresh water. – Example sentence: The lake was formed thousands of years ago by melting glaciers and is now a popular spot for fishing and boating.
Erosion – Erosion is the process by which soil, rock, or other surface material is worn away and transported by wind, water, or ice. – Example sentence: The erosion of the riverbank has created deep channels and changed the course of the river over time.
Geology – Geology is the study of the Earth’s physical structure, history, and the processes that act on it. – Example sentence: In our geology class, we learned how volcanic eruptions can create new landforms.
Climate – Climate refers to the long-term patterns of temperature, humidity, wind, and precipitation in a particular region. – Example sentence: The climate in the desert is characterized by hot days and cool nights with very little rainfall.
River – A river is a large, flowing body of water that usually empties into a sea or ocean. – Example sentence: The river carved a deep canyon through the mountains over millions of years.
Ice – Ice is the solid form of water, often found in glaciers, ice caps, and as frost. – Example sentence: The ice covering the lake melted in the spring, allowing the fish to swim freely again.
Landscape – A landscape is the visible features of an area of land, including its physical elements like mountains, valleys, and bodies of water. – Example sentence: The landscape of the national park includes towering cliffs and lush forests.
Water – Water is a transparent, tasteless, odorless, and nearly colorless chemical substance that is essential for all known forms of life. – Example sentence: Water from the river is used to irrigate the fields and provide drinking water for the town.
Boulders – Boulders are large rocks that have been shaped and moved by natural forces like glaciers or rivers. – Example sentence: The boulders scattered across the landscape were left behind by retreating glaciers thousands of years ago.
