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As Hurricane Ike pummels the Texas coast, the only thing standing in the way is a thin stretch of land called Galveston.
Galveston is a barrier island, a narrow landmass made mostly of sand that extends along a coastline parallel to the land. These islands, common along the Gulf Coast and East Coast of the United States, are some of the most fragile and changing landforms on Earth. And they are particularly vulnerable to storms.
"Barrier islands are exposed to the open ocean, and the waves and storm surges generated by hurricanes," said Bob Morton, a geologist at the U.S. Geological Survey's Center for Coastal and Watershed Studies in St. Petersburg, Fla. "As a storm makes landfall they're the ones that are going to receive the strongest winds and the highest wave actions."
National Hurricane Center officials have warned residents of Galveston to evacuate or else face "certain death," though several thousand are thought to be staying put.
Barrier islands like Galveston are particularly vulnerable to storm damage because they are made of sand, as opposed to the hard bedrock that underlies larger islands and the mainland. They also tend to have very low elevations, making it easy for water to wash over and submerge the island.
Many have questioned the wisdom of choosing to build on and develop barrier islands, given their risks.
"Every year there's reporting on the foolishness of building on barrier islands, but people are going to do it anyway," Morton told LiveScience. "We don't learn from the past. If you look at the barrier islands on the Mississippi coast in particular, after both Hurricane Camille in 1969, and Katrina, what did they do? They rebuilt. It's a perfect example of a coastal area that did get hit as bad as it can get, and they just go back and rebuild."
Barrier islands tend to be even riskier places to live than coastal areas, because they bear the brunt of any approaching storm impact.
"If you think about their location, they're basically lonely sentinels that serve as barriers for the mainland," said Clark Alexander, a marine geologist at Georgia's Skidaway Institute of Oceanography. "Basically you're in a vulnerable spot, because you're located where you get the first effects of anything coming in off the ocean."
Setting up residence in these vulnerable spots is particularly perilous.
"From a safety standpoint, it's silly," Alexander said. "Because the lifespan of a typical house is something like 60 years. But if you live on a barrier island, you can't guarantee you'll have land under your house in 60 years. It's trying to put something permanent in a place that’s very dynamic."
As a result of Hurricane Katrina, a number of barrier islands off the Mississippi coast were completely wiped off the map. Even when storms aren't enough to raze islands completely, barriers often suffer severe damage from storms.
The 1989 Hurricane Hugo wreaked massive havoc on Pawleys Island in South Carolina. Isles Dernieres off the coast of Louisiana was devastated by Hurricane Andrew in 1992. Often, after these storms, people move back and set themselves up for disaster again.
St. George Island on Apalachicola Bay off the Florida coast "has been washed away five or six or eight times and people just keep building back their houses," Alexander said.
For many people living on barrier islands, there is no amount of structural support that can ward off the worst.
"It's important to note that in the big storms, the category 4 or 5 hurricanes, it really doesn't matter how well-constructed your building is," said Orrin Pilkey, a professor emeritus of geology at Duke University, of homes on barrier islands. "And it doesn't matter whether you have a seawall or not. The chances are pretty good that if you have beachfront property, it's history."
Outlook for Galveston
Though Ike might not completely destroy Galveston Island, it could inflict major damage. Already Friday afternoon, the island was being pounded by high waves and flooding. How much depends on how the hurricane develops and what part of the island the eye of the storm passes over.
The eastern part of Galveston Island (also the more densely inhabited) has a strong 18-foot sea wall in place to deflect some of the incoming waves, so it should be more protected than the western half, depending on the extent to which the storm surge overtops the wall.
Galveston was hit hard by Hurricane Alicia in 1983, and was devastated by the "Great Storm" of 1900, when thousands died. After that disaster, a major effort went into fortifying the island against future storms.
"They went in and literally raised the city, propped up houses on stilts," Morton said. "They brought a huge dredge in from Europe and dredged up material and pumped it into the land to build it up. It was an amazing engineering feat for the time. No other place has done something like that." The city also erected a seawall.
Other well-known U.S. barrier islands include the Outer Banks of North Carolina, the islands along the Eastern Shore of Virginia, and even New York's Long Island (though Long Island's northern position makes it less vulnerable to storms than barriers in the Gulf of Mexico and southern Atlantic coast).
The ultimate fate of barrier islands varies, with many gradually retreating landward as eroded sand is pushed back to deposit in the lagoon behind it, and ultimately joining the coast. But some barrier islands with high dunes can avoid this fate.
Galveston is not yet migrating toward the coast, but is in what Morton calls a "narrowing stage," with sand on both sides of the island gradually eroding away. Many barrier islands wax and wane, with sand shifting around and sometimes reducing the land area, but most inhabited barriers are not at risk of being completely destroyed.
"Barrier islands are constantly changing," Morton said. "The barrier islands as a whole are some of the most dynamic landforms on the surface of the Earth."
- Image Gallery: Ike's Fury
- Video - How A Surge Swamps Galveston
- Images: Other Hurricane Destruction