That Sinking Feeling

While government geologists argue over subsidence and sediment loading, the rest of us are wondering: Is the Gulf Coast toast?

September 2005By Comments

IF I INTERPRET IT CORRECTLY, a controversial July 2004 report from the National Oceanic and Atmospheric Administration (NOAA) predicts that Galveston Island will be a memory by the time my great-great-great grandchildren are born. Or maybe it’s their great-great-great grandchildren. We’re speaking here in geological time, and in an arcane, apocalyptic language that is mostly gibberish to laypeople like me. According to one of the report’s co-authors, Louisiana State University geologist Roy Dokka, southern Louisiana is sinking into the Gulf of Mexico at a rate of five feet a century, and the upper coast of Texas can’t be far behind. The good news is that some scientists in other government agencies think Dokka is full of beans. The bad news is that nobody really knows for certain, and even if they did, there’s very little we can do about it.

Nearly everyone agrees that our coasts are vanishing, that sea levels are rising, and that the earth is warming. The question is why. Clearly, the coastal problem is not as bad in Texas as it is in Louisiana, which lost more than four thousand square kilometers of coast during the twentieth century. New Orleans is almost under water already. But so are parts of Houston after a good rain; there are places where the surface level is eight to ten feet lower than it was in 1930. In the community of Surfside, in Brazoria County, you can drive along the beaches and see waves lapping around the pilings of cottages that once stood hundreds of feet from the shoreline. In the village of Treasure Island, just across the San Luis Pass bridge from Galveston Island, homes built fifty yards from the shore in the seventies now stand with their decks overlooking a breakwater instead of a beach (the Gulf shoreline was more than one hundred miles south of Galveston during the last ice age). Thirty miles south of the mouth of the Sabine River, geologists have found evidence of encampments—arrowheads, pottery, mastodon teeth—in 75 feet of water.

Beach loss is caused mainly by erosion, especially surges that accompany hurricanes and tropical storms. The larger problems, however, are rising sea levels and subsidence, the sinking or settling of land, which can be either man-made or natural. Scientists have known since 1926 that land sinks when groundwater, oil, or gas is extracted. Harris County has spent billions of dollars converting from groundwater to surface water, and the Harris-Galveston Coastal Subsidence District has spent about $10 million monitoring subsidence with a network of “benchmarks,” devices anchored to stable places on the earth’s surface to measure elevation and subsidence rates. Ron Neighbors, the district’s general manager, told me that subsidence today is negligible, maybe three quarters of a foot per century. But here’s what makes the NOAA report so controversial and fraught with intrigue: Dokka and his colleagues claim that the real monster is geological subsidence, a force of nature that is inexorable and irreversible.

The Gulf Basin, a giant, seething cauldron of tectonic mischief that extends inland nearly as far as Dallas, started sinking millions of years before man made his appearance, sagging under the weight of billions of tons of sediment pouring down the Mississippi River and Texas rivers like the Trinity, Colorado, Brazos, and Rio Grande. Geologists call this sediment loading: Houston Chronicle reporter Eric Berger likens the phenomenon to a bowling ball weighing down the center of a trampoline. As sediment accumulates and is compacted, the earth’s crust begins to crack under the weight, splintering the subsurface of the basin into thousands of faults and squeezing ancient deposits of salt and soft shale into amazing formations, some of them miles inland. (The numerous salt domes around Houston are the result of this big squeeze; in the deepest part of the Gulf is a mountain range of salt and sediment called the Sigsbee Escarpment, six hundred miles across, rising three thousand feet.) As pressure mounts, parts of the coast slip off into the Gulf through a process known as gravity gliding. Take Galveston: Although sea levels worldwide are rising about a foot a century, the Island is losing more than twice that when subsidence is factored in. “You have to ask, Does Galveston have two and a half feet to lose?” said Houston geologist Art Berman, whose recent article in the Houston Geological Society Bulletin, “The Anatomy of a Silent Disaster,” comes down on the side of Dokka’s research.

On the other hand, research geologist Robert Morton, of the U.S. Geological Survey in St. Petersburg, Florida, told me that Dokka’s research was “scientifically questionable”—a serious allegation against a Ph.D. in geology who is trained in geodesy, the science of measuring the earth’s elevations. Even more damning, Morton suggests that Dokka may be more interested in grabbing headlines than in scholarly pursuit. “Terms like ‘sediment loading’ and ‘gravity gliding’ made perfect sense millions of years ago, but they don’t necessarily apply today,” Morton said. “We know that Galveston Island began forming several thousand years ago, and we know its elevation has not changed much since then. If the rates of subsidence had been as fast [as the NOAA report claims], Galveston would have been permanently submerged a long time ago.”

The quarrel between Dokka and Morton has been roiling for some time, and the NOAA’s National Geodetic Survey, which sets the standards for benchmarks and is the final authority on geodetic measurements in the country, appears caught in the crossfire. “A lot of geologists don’t understand what we do,” said Dave Zilkoski, the NGS’s deputy director. “The report is the best available information on subsidence rates we have. How they are interpreted is something else. Let the geologists work it out.” In a paper released after our conversation, Morton wrote that the rapid subsidence in Louisiana was largely the result of oil and gas production and that there was no evidence that the subsidence that had occurred in the past few thousand years was a result of natural processes like sediment loading and gravity gliding. “The historical rates of subsidence reported by the NGS do not apply to the recent geological past. Therefore, projecting them a century or more into the future without qualification is simply bad science,” Morton concluded. A Dokka colleague replied to Morton’s paper by noting: “The Gulf Basin has been subsiding for one hundred sixty million years. Why would it stop now?” Another Dokka defender said simply, “Morton is pissed because the numbers don’t fit with his preconceived notion. His expertise is in coastal and watershed studies, not in subsurface geology. He’s way out of his league.”

All sides agree on at least one thing: The benchmarks in both states are flawed and outdated. U.S. senator Kay Bailey Hutchison recently pushed for a $665,000 federal grant so that geologists at Texas A&M—Corpus Christi can update the height of Texas benchmarks. This process will require land surveyors to take elevations from somewhere outside the subsidence zone—probably in La Grange or Smithville—and work their way to the coast, at a cost of about $1,000 a mile. Until this happens, debates about sea levels and subsidence rates are strictly hypothetical. The NGS believes that the network it helped build for Harris-Galveston is working well and plans to develop a similar one for Louisiana, which, as the current hurricane season has demonstrated, needs it desperately. When I called Dokka in early July, Hurricane Dennis was roaring toward the Gulf Coast. He had just come from a four-hour meeting with evacuation officials in which he’d tried to convince them that the elevations on some of the evacuation routes were a foot lower than their maps showed. “Our rates are correct, and people need to heed them,” he told me. “People could be killed in a hurricane if they don’t believe elevations have changed.”

Scientific talk makes my head spin, but I saw with my own eyes a glaring example of subsidence in a part of Houston where no groundwater, oil, or gas had been extracted. Art Berman drove me to an area just north of Houston’s Katy Freeway between Gessner and Bingle, where Long Point Fault snakes under the subsurface and occasionally bulges up under the pavement. The fault, which is millions of years old, runs about twenty miles, east to west, and plunges to a depth of perhaps 20,000 feet, yet most residents of this area had no idea it was there until it began to wreck their streets, driveways, and foundations some years ago. In the 1300 block of Moorhead Street, we stopped to inspect a two- to three-foot-high ridge that had broken apart the sidewalk on the east side of the street and plowed up the driveway of a one-story ranch-style home on the west side. “This is what we call a growth fault,” Berman explained. “It will continue to grow as the weight of the sediment loads pulls down on its active side.” Though the Texas coastal plain is one of the flattest places on earth, we spotted “bump” and “dip” signs on most north-south streets from Hedwig Village to Spring Branch, along with cracking driveways, broken sidewalks, and curbs that seemed to be melting into the asphalt. “This is a unique, dynamic basin,” Berman told me. “We have to drill twenty thousand feet to reach a reservoir that everyone agrees was deposited at sea level. So how did it drop twenty thousand feet in a few million years?”

Combating forces of nature is a futile exercise, as is predicting what will happen a century from now, but that doesn’t mean we shouldn’t get real about what’s happening today. Everyone except the fossil-fuel industry and some elements of the Republican party knows that global warming is fact, not theory. In the twentieth century, the earth warmed faster than it has in any period in the past 10,000 years. Nearly every year since 1990 has been hotter than the year before. The Environmental Protection Agency estimates that the earth’s temperature will jump 3 to 9 degrees by 2100 (if that sounds insignificant, consider that during the last ice age, the earth’s average temperature was only 5 degrees cooler than today). Glaciers all over the world are melting. By some estimates, sea level will rise three feet by 2100, threatening not just barrier islands like Galveston but entire nations.

Like subsidence, climate change is a natural process, and scientists are divided over how much of it is influenced by human activity. But nearly everyone agrees that the buildup of carbon dioxide and other greenhouse gases traps heat close to the earth’s surface. It’s been more than 400,000 years since this much carbon dioxide was in the atmosphere. The United States is the only major country that thumbs its nose at the Kyoto accords, which attempt to control carbon emissions. The president insisted as recently as early July that Kyoto would “wreck the U.S. economy,” but his administration hasn’t offered a substitute or even acknowledged that there’s a problem. Quite the contrary: According to the New York Times, the chief of staff for the White House Council on Environmental Quality edited government climate reports to play down links between emissions and global warming.

Misdirection plays might win elections, but refusing to admit that the climate is changing doesn’t mean it’s not changing. Cynicism won’t carry the day in geological time, and it won’t keep Galveston from a watery grave or even give residents of Houston much comfort when they can see the Gulf from their kitchen windows.

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  • Nico

    It’s really not that controversial. Only journalists like you make climatology sound controversial when you say, “This is controversial”. The kind of climate change we’re experiencing is almost unanimously known to to be caused by humans. Someone that knows nothing about the subject saying that they “disagree” because it scares them isn’t a valid scientific retort.