Geo 730: August 11, Day 588: Now That's Slick!

If you looked closely at the cliff below the volcanic neck in yesterday's photo, you might notice it seems to have a lineation to it, a pattern of what appear to be scratches (or you might not, it's subtle). However, in this closer view, the scratches are pretty much unmistakeable. These are slickensides, formed when two surfaces in a fault ground past each other during fault movement- which would have been perceived on the surface as one or more earthquakes. In the case of this cliff, the entire face is slickensided, or "slicked," as geologists sometimes abbreviate the term. Also, this is a fairly typical fault in that there are multiple, roughly parallel, fractures. We often draw or visualize faults as a line, or single break. But actually most larger faults have multiple, interweaving strands, and are more properly referred to as fault zones. When we map an area, a single line will often cover the entire zone at the map scale, but on the ground, as with most things geological, it's a little more complicated than just a single, simple line. (Hammer for scale in lower middle.)

Photo unaltered. June 14, 2014. FlashEarth Location.