Statemap Field Blog, March 31-April 2, 2014

 

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Hello all!

Another great week in the field.  Signs of spring are everywhere, and unfortunately the field season is drawing to a close.  We skipped around all over the Fairfield Bay quad this week, still trying to trace the very thick-, massive-bedded sandstone that we’re calling the base of the Bloyd for now.  Just off the eastern edge of the Fairfield Bay quad is a locally famous outcrop of that sandstone that was supposedly visited by Hernando Desoto himself in 1542.  Whether or not that’s true, it is a very impressive bluff shelter known as the Indian Rock House.  A lot of eroded material was removed from the floor of the shelter when the adjacent Indian Hills Golf Club was built, leaving behind the fine sandstone amphitheater we see today.   One could see how this formation could later become a natural bridge if erosion continues along the joint set parallel to the bluff face.  If that interior arch were to fall out, then the remaining one would form a bridge.  This is how most of the sandstone natural bridges in Arkansas are formed.  Lots of graffiti has been scratched into the friable rock over the years, including some that may have been carved by native people.

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On Tuesday, we finished up our field work on the lake.  We still had a couple islands we needed to visit, and the entire south side of the lake is so steep that access by land would be difficult.  We were excited to find more old river terraces on the islands, including one that would have been deposited on a cut-off meander in the area of Harpers Cove.  The deposit is about 80 feet above and over a half mile north of the current river channel (before the lake was there, that is).  The high end of the range for the downcutting rate for the Colorado River in the western Grand Canyon is 16 centimeters/1000 years, and I think we can all agree that downcutting there probably exceeds that in Arkansas.  Using that rate, an estimated 152,000 years would have passed since that terrace was deposited.  That gravel has been there a long time!  Of course, cutting off the meander would have stranded that deposit at that time, but don’t forget that this stream is developed in bedrock, so meander cut-off would be a fairly infrequent event.  To get a better estimate of these events, methods such as luminescence dating are being developed to age date the sand in these stranded river terraces.  With this new technology, perhaps someday we will know when these terraces were deposited.

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On the south side of lake below Stevens Point is a good example of a modern landslide, and a bit of a cautionary tale.  Sometimes clearing trees for roads and houses can have catastrophic results.  The photo tells the story.  The major part of this landslide occurred March 28, 2005 just after a road was cleared from the house down to the lake.  Most of the material at the edge of the lake on the north side of Hunter Mountain is there as a result of old landslides, therefore any development in this area can cause it to become unstable, as evidenced here.  That’s why part of our project includes mapping areas where landslides have occurred.

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Speaking of Hunter Mountain, we ran across one of the now ubiquitous gas well pads up there, and I thought you might be interested to know the function of each piece of typical well head production equipment.  At each wellhead is a set of valves that regulate the flow of gas.  These are often controlled remotely, thus the solar panels which power the system.  The big tanks near them contain hydrogen sulfide which is introduced into the gas right away to give it a strong odor.  This odor is, of course, quite useful to determine if there are any gas leaks since natural gas is odorless.  From the wellhead, the gas flows to the separators which remove any fluids contained in the gas.  This fluid could include heavy hydrocarbons, but is mostly produced water.  These fluids are stored in large tanks which are built inside a berm.  The berm is designed to hold 1 1/2 times the capacity of one of the storage tanks in case of a spill.  The level in the tanks is also monitored remotely and emptied on a regular basis.  From here, the gas is piped to a compression station where it undergoes further treatment.   Then it is sent through a transmission line and on to your house.  It’s not pretty, but for now, we have to have it.

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Well, next week will be the last of our field season.

Until then, see you on the outcrop!

 

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