Geo 730: August 27, Day 604: Basalt Dike

This is where we generally have lunch- it's not frequented by others, it's nice to have the music of the water in the background, and whether you like sun or shade, you can find a spot that suits you. On top of that, on the bare rock, you don't need to worry about dirt or bugs very much. You can also contemplate the sights and geology as you munch away. In this case I was contemplating the dike beyond Hollie's feet. It's easy to get the impression that sills are horizontal tabular (sheet-like) intrusions, and dikes are vertical. More properly though, sills are conformal with the structure, and dikes cut across structure. In the case of this diorite, all the intrusions, whatever their orientation, are cutting across it. So I consider them all to be dikes. Note that, even on the downstream, protected side of that exposure, the dike is eroded back farther than the surrounding diorite. I should also point out that this is summer low water. The lack of substantial vegetation, and the abundance of rounded cobbles and gravel, indicates that frequently during winter and spring floods, pretty much everything in this photo is inundated and scoured.

Photo unaltered. August 5, 2012. FlashEarth Location.