Columnar Basalts (17.4-6 myo), Frenchman Coulee
April 7, 2013
Basalt columns such as these famous and well-climbed basalts outside Vantage, WA, are formed as lava cooled and fractured. Fracture lines form vertical, polygonal columns often known as “organ pipes” or “postpiles” here in the PNW. This landscape was then carved by some of the largest floods North America has ever seen, which roared through the Columbia Basin dozens of times between 1700 and 1500 years ago. These floods were largely caused by an ice dam at the edge of Glacial Lake Missoula which repeatedly broke and re-froze throughout this period.