Deep winter here is not deep. It is a few weeks in the back half of January and the front of February when the northers come down one after another and the bay goes gray and the grass in the yards gives up and goes the color of a paper sack. The pipes on the outside of the house get wrapped in whatever is in the garage. Somebody's sprinkler system freezes and a sheet of ice forms across a sidewalk on Rollingbrook and everyone drives past it slowly, as if it were an animal. The high school kids stand at the bus stop in shorts and a hoodie because that is what they own. The plants, which are built to run in a hundred and five degrees, put out steam from every seam in the cold, and at dawn the whole complex looks like it is breathing.
It is the season for thinking about what is stored. The propane truck comes up the county roads to fill the tanks at the houses past the city limits. Firewood, if you have a fireplace, which most of us do not. Whatever is in the freezer. What the town does not think about, because it is out of sight and always has been, is one of the largest stores of fuel in the country, which is fifteen minutes up Highway 146 and a few thousand feet straight down.
Mont Belvieu sits on a hill. That is where the name comes from, a low rise that you can barely feel in a car, in a landscape that is otherwise as flat as a table. The hill is there because of what is under it. Under the town, under the high school and the football field and the water tower and City Hall on Town Center Boulevard, is a column of salt. Not a layer. A column. It rises from miles down and comes up close under the surface, a plug of salt a mile or more across, and the ground is humped over it the way a sheet is humped over a knee. It is called the Barbers Hill salt dome, and in the caverns hollowed out of it is the largest store of natural gas liquids in the United States.
I want to go slowly through how the salt got there, because it is the oldest story anyone in this town is standing on.
A long time ago, and I mean this in the way that only geologists mean it, there was no Gulf of Mexico. The continents were still one piece, and they were beginning to pull apart, and the pulling made a low place. Seawater found the low place and came in over a shallow sill, and the climate was hot and the basin was nearly closed, and the water evaporated faster than it could be replaced. When seawater evaporates it leaves salt. It did this over and over, the sea coming in and drying out, coming in and drying out, for a span of time that nobody can picture, until there was a bed of salt on the floor of that young basin thousands of feet thick. Then the basin opened wider and became an ocean, and the rivers of a continent began to pour sand and mud into it, and the salt was buried. This was more than a hundred and fifty million years ago, in the Jurassic. The dinosaurs were in the middle of their long run. There were no flowers yet anywhere on earth.
Salt is lighter than the rock that was piled on top of it. Under enough weight and over enough time, salt does not behave like a stone. It behaves like a very slow liquid. It flows. And a light thing under a heavy thing, given a million years, does what a light thing does: it rises. The salt found weak places in the sediment above it and pushed up through them in great blunt fingers, some of them miles tall, and where a finger came close to the surface it bowed the ground over it into a low hill. There are dozens of these domes along the coast from Texas to Louisiana. Spindletop was one. Barbers Hill is one. The hill you barely feel on 146 is the top of a plume of Jurassic sea salt that has been rising, slowly, the entire time there have been flowers.
Near the surface the salt meets groundwater, and groundwater dissolves it, and what is left behind when the salt goes is the stuff that was mixed in with it, the gypsum and anhydrite and lime that the old sea dropped alongside. Over the top of nearly every dome is a cap of that residue, a hard lid a few hundred feet thick, the dome's own ash. That is what a driller's bit hits first. It is the salt's way of saying it is there.
People found the domes because of oil. Salt is tight, and as it pushed up it bent and broke the rocks around it, and oil and gas that had been moving through those rocks got caught against the flanks of the salt and under the cap. Drillers learned to look for the hills. There was an oil field on Barbers Hill from early in the last century, and for a while the town was a town of derricks, like Goose Creek down the road. What nobody expected was that the salt itself would turn out to be worth more than what was trapped beside it.
Because salt has a second property that matters even more than being light. It is tight. It does not let anything through. And it heals. Crack it, and under the pressure of the rock above it will slowly creep back and close the crack itself. If you wanted to build a container for a liquid under pressure, and you wanted it to be enormous and to last for generations and to leak nothing, you could not do much better than a chamber in solid salt a few thousand feet underground.
So they built them. The way you make a cavern in salt is almost too simple to believe. You drill a well down through the cap and into the dome. You pump fresh water down the well. The water dissolves the salt, and you pump the brine back up, and you keep doing this, water down and brine up, for months, and the hole grows. You can shape it by where you put the water, because water dissolves salt fastest where it is freshest, and by holding a blanket of something the water cannot touch at the top of the hole so that it eats outward and down instead of up. When it is the size you want, which can be the size of a skyscraper stood on its end, you stop. The cavern is finished. There is no concrete in it, no steel liner, no roof. There is only the salt, which has been holding itself up for a hundred and fifty million years and will go on doing it.
Then you fill it. What goes into the caverns at Mont Belvieu is mostly natural gas liquids: ethane, propane, butane, the light molecules that come out of the ground with natural gas or off the top of a refinery column. They are gases at the surface and liquids under pressure, and the pressure a few thousand feet down keeps them liquid. To put product in, brine is pumped out. To take it out, brine is pumped in. The brine sits in ponds and tanks on the surface, waiting, and the caverns breathe in and out through it, product in, brine out, brine in, product out, all day, all year, in a rhythm that the town on top of them never hears. Think for a moment about what is in those ponds. It is the Jurassic sea. It came out of the ground as the salt of a water that dried up before there were flowers, and it has been dissolved again, and it lies in the open in Chambers County under a January sky, and it is doing a job.
Three of the largest pipeline companies in the country operate there, and the pipes come in from every direction. Gas liquids from across the state and beyond arrive at Mont Belvieu mixed, and the first thing that happens to them is that they are sorted. A fractionator is a set of distillation columns, each one warm enough to boil off the next-lightest molecule: ethane comes off first, then propane, then the butanes, then what is left. Each goes into its own cavern. Some of it goes down the road to the crackers on the channel, where ethane is turned into ethylene and ethylene into everything. Some of it goes to the docks and out to the world. When someone in the trade says a price for propane, there is a fair chance the price they mean is the price at Mont Belvieu, because that is where the propane is. A small town with a good school district and a recreation complex on the edge of it is, underground, one of the reference points of the global energy market. The kids at Barbers Hill play football on a Jurassic sea.
I think about this in the cold, because the cold is when the store matters. Propane is a winter fuel. Ethane feeds a cracker that is running through the freeze at the same temperature it runs through August. What is in the caverns is, like the oil in the refinery, what is left of plankton and algae that lived on the surface of a sea and were buried and cooked and became the light molecules now sitting in a hole in salt that was left by a different sea, older still. The container is a hundred and fifty million years old. The contents are older. And the town is using them to get through a Tuesday in January when the bus stop is thirty-eight degrees.
There is a phrase geologists use, deep time, and it is the right one, but it can sound like something you have to go to a canyon to see. You do not. You can see it from the car. The rise in the road at Mont Belvieu is deep time with a drive-through on it. The strange part is that we found a use for it. Somebody looked at a plug of salt that had been rising through the crust since before there were flowers, and thought: that would hold things. The salt was not put there for us. Nothing was. But we are a way of looking at the world that finds the hollow in the thing and fills it, and there is something in that which is not only practical.
On the coldest night of the winter, drive up 146 after dark. The lights of the terminals come up on the left and the right, white and orange, and the tanks and the brine ponds and the pipe racks go by and then the town, and then the dark again toward the Trinity. There is nothing to see of the caverns. There never will be. They are thousands of feet beneath the truck stop, full and silent, in salt that has not seen the sky since the world was a different shape. Above them the ground is frozen an inch down, and the frost is on the football field, and in the morning the sun will come over the bay and take it off in an hour, the way it always has.