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Sep 15 / Dave Schumaker

How Barrier Islands (Such as Galveston) Work

Judge Ed Emmett, chief executive of Harris County, Texas was quoted in a CNN article about the damage that Hurricane Ike left behind in Galveston.

“Galveston Island is called a barrier island for a reason. It served as a barrier for Houston.”

So what exactly is a barrier island? (See HowStuffWorks: How Barrier Islands Work)

Barrier islands are narrow strips of land that parallel the coastline and consist of a variety of fine sediments and particulate matter. A barrier island is separated from land by a shallow bay or lagoon and can stretch for tens of miles.


Source: University of Texas

How long barrier islands have existed how they are formed is not well understood.

The formation of barrier islands is complex and not completely understood. The current theory is that barrier islands were formed about 18,000 years ago when the last Ice Age ended. As the glaciers melted and receded, the sea levels began to rise, and flooded areas behind the beach ridges at that time. The rising waters carried sediments from those beach ridges and deposited them along shallow areas just off the new coast lines. Waves and currents continued to bring in sediments that built up, forming the barrier islands. In addition, rivers washed sediments from the mainland that settled behind the islands and helped build them up.

In recent history, we’ve seen human development encroach on barrier islands, often with disastrous results when hurricanes occur. This article from Live Science talks about the foolishness of building on barrier islands.

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.

For comparison, the USGS has a web page showing the effects of Hurricane Katrina on Louisiana’s Barrier Islands.


This photo shows the aftermath of Hurricane Ike on Galveston Island.
Source: AP

Here is a video that shows the effects of a hurricane on a barrier island. This particular video is from Hurricane Ivan in 2004 and the Pensacola Beach barrier islands.

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