Witches' Brew

After seeing the result of Hurricane Katrina on the news over the past week, I've been thinking back to when I visited Louisiana on a brief geological excursion on Saturday 9th March 2002. I've typed up the following from the scruffy notes in my jotter.

+++++++++

We drove in a coach from Houston to Morgan City on the Gulf Coast and stayed in a white, clap-board hotel. I was struck mainly by how flat and featureless the place was. A title for a poem came into my head: 'Calibrated to Flat'.

All the way there: long straight roads and a sign board every so often advertised a crawfish restaurant or a tyre-changng place. That evening we ate in a salad bar type restaurant. An 'eat-as-much-as-you-can' style joint with a great view of an enormous car park.

The next day, we visited Six Mile Lake. This lake used to be some eighty kilometres long, but is now just a couple of kilometers in length. It has been filled during the last hundred and fifty years or so by sediment diverted from the main course of the Mississippi River in 1839. This was no accident, but rather an attempt to prevent flooding of New Orleans.

Our guide told us a bit about the Pleistocene history of the Mississippi, which is recorded by the fill of a huge valley cut and filled during and after the last ice age around 10,000 years ago. The sediment-filled valley is up to 450 feet deep and 70 miles wide. The Mississippi is a huge river, fed from all over the North American Craton from the Rockies in the West to the Finger Lakes in the North. In the last ten thousand years or so, the sediment it carries has built a delta which is about 300 miles wide.

We stopped at Six Mile Lake. One of the first things that our guide told us about was the hurricane threat to New Orleans. He called it 'a witches' brew'. Of a total population who live in the flood zone, there are 200,000 who don't have cars and a further 100,000 who are disabled. People are told, apparently, to keep a chainsaw in their attic in readiness for the floods that may come when a hurricane driven tidal wave drives water back up the Mississippi and bursts the 5m high levees. Being trapped in your attic with flood water rising through the house is clearly a situation to avoid. He also mentioned the 'killer mold' which can infest homes when they become flooded. The Stachybotrys Mold releases toxigenic spores that are potentially dangerous to humans, especially if they enter an air-conditioning system.

"In 2000", he said, "there were three major loss-of-life threats in America: the World Trade Centre, The San Andreas fault zone and a New Orleans flood. the World Trade Centre is no more, so now there are only two."

We drove down to Patterson where we would take a small motorboat out to the Wax Lake Delta, an embryonic delta that has been created by man following the cutting of a canal some 400m wide from Six Mile Lake to the sea, a distance of about 20 km. Since 1973, the delta has built out around 5 km into the Gulf of Mexico.

Signs outside shops advertised: "Beer Gas Bait" or simply "Tackle". Our guide pointed out to us that Cypress trees indicate areas that might potentially flood. The trees were hung with a pale green lacey plant called Spanish Moss, a curious epiphyte plant, very simple and ancient. It was once used as material for stuffing the seats of Model-T Ford cars. Moping black cormorants sat on the cypress tree branches.

Our guide continued talking about the hurrican threat, telling us that when a large, established delta mouth bar is drowned, a system of barrier islands is created at the outer edge of the delta lobe. These barrier islands out in the Gulf of Mexico can be maintained, but it costs money. Geologically they are unstable, because the delta lobes are slowly sinking due to compaction. Barrier islands, however are "the last line of defence from hurricanes".

Driving in the bus, we passed a sort of compound containing a load of little brick houses, very basic, all the same design. "These houses are all below sea level" remarked our guide. I glimpsed a group of black children playing on the gravel track.

We arrived at Wax Lake Landing, passing trailer homes on piles of bricks. There were several 4x4 pickups, Dodges and Chevrolets, parked on the grass and a couple of white men were just then backing their Fishmaster boat into the water before loading up with guns, dogs and beer. Off for a wildfowl shoot.

A US stars and stripes flag was trying to fly, but had got caught up in a cypress tree by the river. I walked out along the little jetty, and when I looked down from the side, I could see the carcass of a small dog lying in the mud, its yellow ribs poking through matted fur. A plume of silt was sweeping along the riverbank in the brown water and, close by, a dredging boat lay rusting like burnt paper, the bottom of its dredge bucket corroded to intricate lacework. In the eroding riverbank, between layers of chocolate-coloured mud, I noticed a layer of brilliant white shells being slowly revealed.

We got into the boats and headed off, passing underneath a vast pipeline carrying oil, which was strung over our heads on great metal poles and tension cables. The river was incredibly wide, grey and featureless. Drab beds of reeds and scrubby trees rose up on either side, puntuated here and there by a rusted boat, a hunting hide or a white egret out searching for dinner. The flat-bottomed skiff bumped along on the choppy waters. I had already got myself sunburnt standing for an hour by the lake earlier in the day. Now the sky was looking threatening. We crossed the Intracoastal Canal, another huge waterway, this one a 1000 miles long. It allows large boats to pass along the Gulf Coast without ever heading out to sea.

As we neared the coast, we were engulfed by mist, then we landed on one of the delta mouth bars, climbing out onto firm ground with reeds and scrubby trees. We drilled a core down into the delta mouth sediment, which was only a few metres thick, surprisingly, considering the size of the river. It seems that it shallows significantly as it nears the sea. The sediment was chocolate brown again, with thin bands of plastic clay.

When we got back into the boat, it started to rain, and by the time we got back to the landing, I was soaked to the skin. As soon as we had landed, the rain stopped and I was able to strip off some clothes and wring them out. We ate some sandwiches, watched the craft being hauled from the water, and got back on the bus which would take us back to Houston.

The road back was long and straight. On the way there, we stopped at a Crawfish restaurant. I don't remember what I ate. I was tired, sunburnt and wet. Crawfish I expect.