Monday, October 12, 2009

Whose Fault Is It?

We joined the Kentucky Society for Natural History on their fall conference at Reelfoot Lake this weekend. As we packed the car on Thursday morning, a quick glance at the weather map showed bright areas of green, yellow and red between Louisville and Colorado. It's going to be a rough weekend, we agreed. Indeed, as we explored the New Madrid fault region, we drove through miles and miles of rain. In addition to being wet, we spent the weekend without technology! Our T-Mobile phones had no signal at all, and the resort where we stayed, although very nice otherwise, had no Internet connections. This was truly a test of our dedication to nature studies! If you aren't familiar with history of the area, New Madrid, MO, was the epicenter of the worst earthquakes in the United States, in 1811 and 1812. The fault was created by a rift that failed about 500 million years ago, and the rift valley filled with sediment. The actual fault is about 25 miles underground, so you don't see evidence of faulting as you would in California, for instance.

Fortunately, the center of the country was relatively unpopulated at that time, when earthquakes exceeding 7 and 8 on the current Richter scale struck over a 3 month period. The fault crosses under the Mississippi River in several places, and uplifting caused the river itself to flow upstream for a while. Liquefied sand erupted in large geysers. The quakes were felt as far away as Canada. I-55 has a rest stop at the site of the epicenter, although they don't publicize it.

Will there be another quake here? Sure, but no one knows when. The damage will be catastrophic when it hits this time, given the size and nearness of cities like St. Louis, Memphis, Nashville and, yes, Louisville. A relatively small quake in April 2008 was centered in Illinois, felt in Louisville, and arose from the New Madrid fault system. Seismometers in the area show unfelt earthquakes occurring regularly. NOVA has a good online video about the New Madrid fault system.

The river itself is not exactly what I expected. The Army Corps of Engineers has turned the Ohio River into a series of lakes using dams and locks. Their goal is to maintain a navigation channel nine feet deep at all times. We call it the Ohio Lake here in Louisville.

The Mississippi River also has dams for navigation, but in between the dams the river twists and turns as it did in the days of Mark Twain. We watched a fully loaded coal barge turn almost sideways to make a turn around a large sand bar. A towboat pushing a full load of fifteen barges is like trying to steer three football fields, 365 days a year, in all kinds of weather. The map above shows some of the channels from the last 250 years. Oxbow lakes, such as Reelfoot, are left as the channel changes directions. The land is perfectly flat and fertile, so farmers plant great fields of corn, soybeans and cotton. Migrating Tree Swallows swoop after insects we can't even see, then perch on the power lines. I saw more Kestrels this weekend than ever before.

We drove downstream to the nearest bridge, then up the Missouri bootheel through the fault zone. Not wanting to drive that far again to get back to Reelfoot, we got to ride the Hickman Ferry across the river, back to the Kentucky side. The small boat you see on the side of this photo is on a hinge. When we pulled away from shore, this part swung out and around, so it could push across the river in a forward direction, just as it did on the way to pick us all up.

My next postings will all be about our weekend at Reelfoot, and the cypress swamps and wildlife we enjoyed.

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