Saturday, August 21, 2010

Creek Rocks

When the water disappears from the creek, what’s left is mainly rocks. I don’t know nearly enough about geology. I know the basic rock types and the common minerals and understand the role the bedrock plays in the development of soils and the landscape, but when I look at a jumble of rock such as this, I feel that I’m missing some crucial connection. It doesn’t help that so much of the rock is hidden from view by the plants and soil. The creek is where I go to try for a meaningful bond between myself and the elusive subterranean structures.

The exposed creek bed becomes new territory that can be exploited by pioneering plants. Seeds are constantly being moved downstream by the water. In large creek or river systems, seeds are carried by flood water far out into the floodplains where they can grow and establish new colonies. In small creeks like these, the seeds are more likely to become lodged between the rocks or on the gravel bars. Neither of these locations is ideal for long term survival, so the best chance for developing permanent colonies comes from plants in the creek bed maturing and spreading seed outward to the area immediately above the creek bank. Seed falling into the creek bed will most likely move on downstream.

Autumn is the best time to see exposed bedrock features in the creek. Because of the disturbance caused by the meteor impact, most areas appear to be rough and jagged. If I were to put names to these features I would most likely use terms like Gator’s Back or Cat’s Tongue.

Some tilted bedrock slabs are causing the subsurface flow to come to light. This is the trickle of water that is moving through the remaining pools. The water stream is only about two inches across.

I was asked why I spent so much time taking pictures of the creek and I replied that it was the coolest place to be on a hot August day. The big rock slabs bring up the coolness of the earth and when the breeze blows it feels like the flow from an air conditioner. I’m just like any other animal seeking out the most comfortable location.

The unorthodox bedrock in this area results in some pretty odd groundwater patterns. Subsurface water typically follows the plane of the bedrock layers and those layers are expected to closely follow a nearly horizontal orientation. At Blue Jay Barrens, the bedrock may tip in any direction and has many abrupt changes. Downward slanting layers can capture subsurface water and direct the flow deep underground. This means that some sections of the creek can go dry while flow remains both upstream and downstream of the dry section.

Level is not a concept that applies much at Blue Jay Barrens. People sometimes look at my photos and assume that I can’t hold the camera straight. I’m not personally responsible for the tilting bedrock, leaning trees or sloping ground. The tree in the top center background is straight and vertical. By using that tree as a guide, you can see that the camera was level when the shot was taken.


  1. "the disturbance caused by the meteor impact"

    Is there an earlier post that this refers to?

  2. I give a little background on the impact in a post on breccia in June of 2009. You can find it here

    For the most current research on the subject, I would recommend Report of Investigations No. 146 "Subsurface Geology of the Serpent Mound Disturbance of Adams, Highland, and Pike Counties, Ohio." Ohio Department of Natural Resources,Division of Geological Survey.

  3. Glad you posted that link, because I too went "Meteor impact? What?!" when reading this. :)

  4. Creek rocks are interesting,and I found some yesterday in northern Richland County that have fossils in them.

  5. Hi, Jana. Finding fossils is a lot of fun. I rarely find any fossils in my creeks. The rocks must be of the wrong age.