Tuesday, January 1, 2013

Giant Columns and Palagonite

I was going through some old photo slides and came across a couple of the Columbia River Basalt Group in eastern Washington from a past field trip. Both images were taken east of the Columbia River east of Vantage.
Orange palagonite and pillow basalt
This first site is an example of lava flowing into a lake. The orange palagonite forms from the shattered basalt fragments formed as the lava flowed into water. The site is just up Sand Hollow on State Highway 26 just east of the junction with State Highway 243. Given the presence of rivers and likely lakes as well, lava flows into water are not uncommon in eastern Washington Columbia Basalt Group. Besides this site there are numerous examples within the road cuts of Interstate 90 between Vantage and Rye Grass Summit east of Ellensburg. Tom Foster has a nice post with way better pictures of this exact spot as well as other sites on his Ice Age Floods Blog basaltic-lava-pillows-pillow-basalts.
The other site is a famous site amongst northwest geologists. Giant basalt columns standing in a single line. 

Columnar basalt at Frenchman Coulee
Frenchman Coulee is one of several dry canyons carved by the great Missoula Floods as part of the flood waters poured over the cliff walls on the east side of the Columbia River. The floods carved the landscape here with what must have been a spectacular water fall that somehow left a single line of columns standing between the receding cataracts.
A great spot to study flood basalts, Missoula Floods and perhaps some of the later floods that surged down the Columbia Valley. The site is accessed off of Interstate 90 via Silica Road and then Vantage Road. Silica Road is a reference to some open pit mining in the area that mined diatom deposits formed in lakes between lava flow events.

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