Missoula Floods: How Did This Get Here?

Granite Erratic in Pasco Basin, Washington

The Central Washington Basin is covered with layers of basalt, totaling as much as 2 miles thick, created by huge lava flows 8-15 million years ago.  The nearest source of granite rock is several hundred miles away.  This photo was taken near the Hanford site north of Richland.  The granite rock was about 1/4 mile from the road.  My lens combination was 560mm.  For reference, the actual height of the rock (above ground) is about 12 feet.  It is a big granite rock.  How did it get here???

The current theory is that it was brought here as part of the ice dam that broke loose during one of the Missoula floods around 15,000 years ago.  As the ice melted, embedded rocks were released.  The Pasco basin and its surround hills have many such erratics.

Leave a Reply

Your email address will not be published. Required fields are marked *