Thursday, September 30, 2010

Partial Repost: Basalt Dike with Sideways Columns

I was inspired earlier this morning, while reading the most recent columnar post over at Geotripper, to rejoin the current geoblogospheric meme on columnar joints with a partial repost of photos I took last October. This basalt dike can be seen right along the east side of Highway 139, just south of Lassen County Milepost 52 (Google Maps location), and just before you get to the Willow Creek Campground if you're driving north.
The columnar jointing in the dike is nearly horizontal, making the rock look like a bunch of stacked logs.

Looking end-on at the pile of stacked logs, the cross-section through the stacked columns shows the typical, though is this case irregular, polygonal shapes common to basalt columns.

NOTE: Lockwood has a good running list of blog posts for this meme. Additionally, Kim posted about a dike with horizontal columnar joints in early 2009, and Andrew's article on basalt columns has a great photo of a piece of basalt with an almost perfect hexagonal shape.


Alaska Al said...

I view this as a triple dike of 3 different ages. I believe the age distinction can be based on the relative "freshness" of the three. It has been a long time, 5 to 10 years, since I have visited this outcrop but my recollection is that the dike on the left is the oldest.

Silver Fox said...

Obviously I'm going to have to stop and look at this dike - or set of dikes - more closely next time! It's such a fine outcrop. Hard to imagine taking a rock hammer to it, but I will!