An Odd Column

This enigmatic column of basalt that was found near Hog Lake in Washington State. The interesting thing about this columnar basalt is that there is nothing around it that looks similar. According to the scans of the rock, with the use of a calibration developed with Bruker and EWU (Evart and Pritchard, 2016), it appears to be a part of the Priest Rapids Member of the Wanapum Basalt Formation which would have formed around 14.8 million years ago (Reidel, 2015). The Priest Rapids Member makes up about 27.3% of the Wanapum Formation and the Wanapum Basalt Formation makes up about 5.8% of the Colombia River Basalt Group (Reidel, 2015). Even though these are small percentages, the Priest Rapids Member has a volume of around 2800 km3 making it one of the largest member of the entire Colombia River Basalt Group (Reidel, 2015). Included is the scan of levels of zirconium and strontium of the sample that was taken from the rock that shows that the rock is a part of the Priest Rapids Member.

The big question about this column of basalt is “How did this get here?” One answer is that humans played a part. But since it is an anomaly in the area (it is off the path, people would need tools to move it, no apparent purpose for it being where it is) there could be another reason for the placement of the rock; most likely being an Ice Age Flood.

When there are large floods, like those that would happen with the Missoula Floods, a process called plucking may occur. Columnar basalt are surrounded by joints. Joints are cracks or fractures where rocks get pulled apart and form the border between each complete unit of columnar basalt. Like pizza after it has been cut, the joints make it so the columns are easily pulled apart. The force that most likely pulled the Hog Lake sample is plucking from Kolks during a flood, illustrated in the attached figure from Baker (2009). When large floods occur, they can wash away the top layer of loose rock and sediments, exposing bed rock in the process. In deeper water the turbulent water can form vortices, or underwater tornadoes, with the decreased velocity and pressure that suck up and eject columns from the bed rock and send them into the water. The flood then can deposit the rock wherever in the flow. This can happen with glaciers, but on a much smaller scale than the Ice Age floods.

Going back to the sample found near Hog Lake, a possible reason that the enigmatic is here is through the plucking process, illustrated in the attached figure from Baker (2009). A kolk could have put the column of basalt into a flood, a part of the Missoula Floods, which eventually deposited it next to Hog Lake. However, people do some crazy things!