How volcanoes shaped the Tri-Cities
Twisted Columbia River Basalt lava flows next to Devils Canyon Road south of Kahlotus, Washington / Photo by L. Guy McWethy, WGS/DNR
As you walk around Richland, Kennewick, and Pasco, you’re almost guaranteed to come across decorative blocks of rocks. Usually, they’re brown to black in color, standing up in columns or angular blocks. If you hike to the top of Badger Mountain, you may have sat upon a polished, hexagonal bench made from this kind of rock. And if you pay attention to the gravel along many sidewalks and slopes, you’ll notice the same dark black to brown rock. Geologists have named it Columbia River Basalt.
Columbia River Basalt is so ubiquitous in the Tri-Cities and surrounding area because it is the most common bedrock — the solid rock underneath the soil — in the area. Exposed in some areas along the Columbia River, this rock formation spans 60,000 square miles across Washington, Oregon, and Idaho. At its thickest point just west of the Tri-Cities, it is estimated to be more than 13,000 feet thick.
Basalt is an igneous rock that forms as magma or lava from a volcanic eruption cools and solidifies. Columbia River Basalt erupted approximately 16.7 million years ago from volcanic fissures near the present-day border between Washington, Oregon, and Idaho. While it’s impossible to compare that timeframe with the human lifespan, Columbia River Basalt is actually the youngest continental basalt flow on Earth.
Geologists refer to it as a ‘flow basalt’ because, as the volcanic fissures erupted, the lava was runny enough to flow and ‘flood’ the landscape before solidifying. As the lava cooled into basalt, uneven cooling caused some areas to cool faster than others, leading the rock to crack at specific and consistent angles. This cooling pattern is called columnar jointing, forming the five- to seven-sided prisms or columns proudly displayed across the Tri-Cities. You can see these columns in situ in many places nearby, including Othello and Devil’s Monument.
For the volcanic cracks to have erupted the lava, they needed a source of heat. In this case, it was provided by a hotspot, which is a location within the Earth’s mantle where the mantle is unusually hot. Hot spots can melt the crust — the surface layer of the planet — above the hotspot and generate volcanoes. The mantle is a semi-solid layer directly below the crust that the crust floats on, akin to a piece of paper floating in a bucket of water. A classic example of a hotspot is Hawaiʻi, which is composed entirely of islands generated by hotspot volcanoes. The hotspot that created the Columbia River Basalt is believed to be the same one that is now underneath Yellowstone, heating the hot springs and geysers like Old Faithful.
Columbia River Basalt is by no means the only rock in the Tri-Cities, just the oldest one we can still see at the surface. The basalt forms the foundation of the Tri-Cities and southeastern Washington. Its distinct columnar shape has become a defining symbol for the region, and its abundance makes it a cheap option for gravel and other rock fill. The Columbia River Basalt changed the course of the Columbia River, as its immense weight caused the region to sink minutely. The basalt may have even had a hand in the creation of the Hanford nuclear site, as its particular shape and stability met the environmental conditions for the federal government’s Manhattan Project.
Columbia River Basalt is only one piece of the geologic puzzle that makes up the Tri-Cities we know today. But it is such an important one! The more you look around, the more geology you’ll see that makes up our environment. Keep an eye out!
Elliz is a geologist and avid birdwatcher who loves to collect cool rocks.
References:
Cascades Volcano Observatory. “Columbia River Basalt Group Stretches from Oregon to Idaho.” USGS, United States Geological Survey, 7 Dec. 2023, usgs.gov/observatories/cvo/science/columbia-river-basalt-group-stretches-oregon-idaho
“Columbia River Flood Basalt Volcanism.” WA 100 Colombia Basin, Washington DNR, wa100.dnr.wa.gov/columbia-basin/flood-basalts
“Columbia River: Description, Creation, and Discovery.” NW Council, Northwest Power and Conservation Council, nwcouncil.org/reports/columbia-river-history/columbiariver