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Geology of the Columbia River Gorge

The Columbia River Gorge is a breathtaking canyon that stretches over 80 miles through the Pacific Northwest, separating the states of Oregon and Washington. With its steep cliffs, cascading waterfalls, and towering mountains, the gorge is a favorite destination for outdoor enthusiasts, hikers, and geology enthusiasts alike.

The geology of the Columbia River Gorge is as fascinating as it is stunning. The area’s rock formations tell the story of millions of years of geological activity, from ancient lava flows to cataclysmic floods.

One of the most distinctive features of the gorge is its basalt cliffs. These cliffs were formed by a series of volcanic eruptions that occurred between 15 and 17 million years ago, during the Miocene epoch. The eruptions, which occurred in what is now eastern Oregon and Washington, created massive lava flows that covered thousands of square miles. Over time, these lava flows cooled and solidified, creating the basalt cliffs that we see today.

The Columbia River Gorge is characterized by its steep basalt cliffs, which rise hundreds of feet above the river. These cliffs are made up of layers of basalt, which were formed by successive volcanic eruptions that occurred over millions of years.

The layers of basalt in the Columbia River Gorge are arranged in a series of horizontal sheets, which are called basalt flows. Each flow represents a single volcanic eruption, and they can vary in thickness from a few feet to several hundred feet. In some places, there may be dozens of individual flows stacked on top of each other, creating massive cliffs that can reach heights of over 2,000 feet.

The basalt flows in the Columbia River Gorge are composed of a type of volcanic rock called flood basalt. Flood basalts are created by massive, effusive volcanic eruptions that release enormous amounts of lava onto the Earth’s surface. The lava flows out in sheets and spreads over a large area, creating flat-lying layers of rock.

One of the unique features of the basalt flows in the Columbia River Gorge is their composition. Most of the basalt in the gorge is what geologists call tholeiitic basalt, which is a type of basalt that is rich in iron and magnesium. Tholeiitic basalt is typically associated with oceanic crust and is thought to have formed from magma that originated in the Earth’s mantle.

The layers of basalt in the Columbia River Gorge are not all the same. While they are all composed of tholeiitic basalt, there are variations in their composition and texture. For example, some flows are very dense and crystalline, while others are more porous and contain numerous gas bubbles. Some flows are also heavily weathered, while others are relatively fresh.

Overall, the layers of basalt in the Columbia River Gorge are a testament to the region’s volcanic past and the incredible forces that have shaped the landscape over millions of years. They are a fascinating reminder of the power of nature and the incredible geological history of our planet.

Another fascinating geological feature of the Columbia River Gorge is its waterfalls. Many of these waterfalls are formed by basalt layers that are more resistant to erosion than the surrounding rock. As the softer rock is eroded away by the powerful flow of the Columbia River, the harder basalt layers remain, creating spectacular cascades like Multnomah Falls, which drops over 600 feet in two tiers.

In addition to its volcanic and erosional features, the Columbia River Gorge is also known for its massive floods. These floods, which occurred between 15,000 and 18,000 years ago, were caused by the melting of glaciers during the last Ice Age. As the glaciers melted, enormous amounts of water were released, creating catastrophic floods that swept across the Pacific Northwest. These floods, known as the Missoula Floods, scoured the landscape of the Columbia River Gorge, creating the steep cliffs and dramatic features that we see today.

The columnar basalt and cuboidal basalt formations that you might see in the Columbia River Gorge are both the result of the same geological process: the cooling and solidification of lava.

When lava flows out of a volcanic vent and onto the Earth’s surface, it starts to cool and solidify. As it cools, the lava contracts and cracks, much like how mud cracks as it dries. These cracks form hexagonal patterns, which are the basis for the columnar basalt formations.

Columnar basalt forms when lava cools slowly and evenly, allowing the cracks to continue forming and extend downward. The columns can be several feet in diameter and can extend down dozens of feet, creating impressive formations that look almost like giant organ pipes. The columns can be straight or curved, depending on the specific conditions of the cooling lava.

Cuboidal basalt, on the other hand, forms when lava cools more rapidly and unevenly, causing it to crack in a more angular pattern. The cracks create cubes or rectangular blocks of basalt that can be stacked on top of each other, forming formations that look almost like building blocks.

The specific conditions of the lava flow and cooling process can influence whether columnar or cuboidal basalt forms. Factors such as the temperature of the lava, the rate of cooling, and the mineral content of the lava can all contribute to the final shape and pattern of the basalt formations.

Both columnar and cuboidal basalt formations are common in the Columbia River Gorge, and they are a testament to the region’s rich geological history and the incredible power of volcanic activity.

Overall, the geology of the Columbia River Gorge is a testament to the power of nature and the incredible forces that have shaped our planet over millions of years. Whether you’re a geology enthusiast, hiker, or just someone who appreciates natural beauty, the gorge is a must-see destination that offers a glimpse into the fascinating history of our planet.

a large waterfall over some water

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