When did the Columbia River basalts form?

The Columbia River Basalts: When the Earth Went Wild in the Northwest

Picture this: vast stretches of the Pacific Northwest, once a relatively normal landscape, suddenly ripped open, spewing molten rock like a scene from a disaster movie. That’s essentially what happened when the Columbia River Basalt Group (CRBG) formed. This wasn’t just a regular volcanic eruption; it was one of the biggest volcanic events to ever hit North America. We’re talking about southeast Washington, northeast Oregon, western Idaho—all buried under layers of basalt.

So, when did this all go down? Well, the main action happened between 17 million and 6 million years ago. But get this: the real fireworks, the period when over 99% of the basalt flooded the region, was crammed into a mere 3 million years, from 17 to 14 million years ago. Can you imagine the sheer scale of that? It must have been an absolutely insane period.

Breaking Down the Basalt Bonanza

Now, the CRBG isn’t just one giant blob of rock. It’s more like a layered cake, with different formations representing different phases of the eruption. Each layer has its own unique chemical fingerprint and story to tell. Here are a few of the headliners:

• Steens Basalt: Think of this as the opening act. It kicked things off around 16.6 million years ago in southeast Oregon. But, hold on, some recent studies suggest it might have started even earlier, maybe around 17.2 million years ago.
• Imnaha Basalt: Next up, the Imnaha Basalt flowed over the Steens Basalt, roughly 16.6 to 16.5 million years ago.
• Grande Ronde Basalt: Now we’re talking! This is the headliner, the rock star of the CRBG. It accounts for a whopping 90% of the total volume. Deposited between 16.5 and 16.1 million years ago, it blanketed an area of about 163,700 square kilometers. That’s like covering the state of Florida three times over!
• Wanapum Basalt: Following the Grande Ronde’s epic performance, the Wanapum Basalt took the stage between 16.1 and 15.9 million years ago.
• Saddle Mountains Basalt: And finally, the encore. The Saddle Mountains Basalt represents the last major eruptive phase, stretching from 15.9 to 6 million years ago.

Cracking the Code: How We Know the Dates

So, how do scientists figure out when all this happened? It’s not like they were there with stopwatches! They use some pretty cool techniques:

• Radiometric Dating: This is like a geological clock. Methods like 40Ar/39Ar dating measure the decay of radioactive elements in the basalt, giving us a pretty accurate age. They also use U-Pb dating on volcanic ash.
• Stratigraphy: Think of this as reading the rock layers like pages in a book. By looking at the different layers and their characteristics, scientists can figure out the relative order of events.
• Magnetostratigraphy: This one’s a bit more out there. It uses the magnetic polarity of the basalt layers, comparing them to a known timeline of Earth’s magnetic field reversals. Pretty neat, huh?

The Yellowstone Connection: A Volcanic Family Tree

Here’s where it gets really interesting. Scientists believe the CRBG is linked to the Yellowstone hotspot, that famous volcanic area currently chilling out under Yellowstone National Park. The theory is that this hotspot, a plume of hot rock rising from deep within the Earth, triggered the massive basalt eruptions. As the North American plate drifted over the hotspot, the volcanism shifted, eventually leading to the formation of Yellowstone as we know it today.

A Lasting Legacy: Shaping the Northwest

The Columbia River Basalts didn’t just disappear after they erupted. They fundamentally reshaped the landscape of the Pacific Northwest. The sheer weight of the lava caused the ground to sink, creating the Columbia Basin. The eruptions also forced the Columbia River to carve out its modern path. And, of course, we can’t forget the stunning geological features like the Columbia River Gorge and the Channeled Scablands, sculpted by those ancient lava flows and later shaped by the Missoula Floods.

Even now, scientists are still digging into the CRBG, trying to understand the nitty-gritty details of the eruptions, how they might have affected the climate, and what exactly caused this incredible volcanic outburst. It’s a story that’s still being written, one basalt layer at a time.