Formation of Columnar Basalt is quickly described in this 2 Minute Geology episode.
Columnar Basalt is the result of cooling and cracking of an unusually thick basaltic lava flow. Columns are often 50 feet high or more! The Columbia River Basalt Group of Washington and Oregon (USA) is a stack of more than 300 individual lava flows. The flows issued forth from deep fissures that began forming 17 million years ago in southeast Washington and northeast Oregon. Columns are well-developed in some of the flows and non-existant in many others. The Roza Flow is the most famous Columbia River Basalt flow for column formation. Notable columns around the world include Devil's Tower in Wyoming and Giant's Causeway in Ireland.
This episode begins with Nick at the foot of some Columnar Basalt in the Columbia Wildlife Refuge northeast of Othello, WA. The Elephant Mountain basalt flow is featured - a flow that has particularly beautiful columns, although the columns are thinner than Roza columns. This region - the Drumheller Channels - was hit hard by the Ice Age Floods that swept through the area between 17,000 and 15,000 years ago. The floods took many columns away, but these majestic columns remain. Lower Crab Creek is nearby - an old course of the Columbia River.
The episode continues with Nick climbing to the top of the Elephant Mountain flow. The tops of columns have well-defined polygonal shapes: pentagons, hexagons, octagons, etc. Cracks with these shapes in nature usually indicate contraction of surfaces - in this case, a cooling lava flow that took perhaps up to 100 years to completely cool. Columnar Basalt forms in the lower section of basalt flows - know as the Colonnade. Higher in basalt flows, a more densely clustered sets of joints and fractures - the Entablature - suggests a more intricate and complicated cooling history of the lava long ago.
Filmed in September, 2012
Episode written by Nick Zentner and Tom Foster.
Video, Sound, & Editing: Tom Foster