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St. Petersburg Coastal and Marine Science Center > Coastal Change Hazards: Hurricanes and Extreme Storms > Hurricane Isaac

Coastal Change Hazards: Hurricanes and Extreme Storms

Hurricane Issac

Pre- and Post-Storm Photo Comparisons - Chandeleur Islands, Louisiana and Dauphin Island, Alabama

Hurricane Isaac made landfall in southeastern Louisiana near the mouth of the Mississippi River on August 29, 2012. It was a relatively weak Saffir-Simpson Scale Category 1 hurricane with peak-sustained winds of 70 Knots (or 80 MPH). However, the storm's large size and slow speed as it approached the coast allowed it to impact the coast over many hours, much like a winter storm. In the storm's right-front quadrant, where the winds were onshore and strongest, storm surge and superimposed waves inundated and overwashed the barrier islands that lie to the east of the River, e.g. the Chandeleur Islands, LA and Dauphin Island, AL, both severely impacted during 2005's Hurricane Katrina. During Isaac, these islands suffered considerable changes, including the apparent destruction of remnants of the oil protection berm built on the Chandeleurs after the Deepwater Horizon oil spill. Changes are visualized in comparisons of pre-Isaac (August 8, 2012) and post-Isaac (September 2, 2012) aerial photos.

Location Map
Location Map.

Dauphin Island, Alabama

pre- and post-storm photos
Location 1: Oblique aerial photographs of Dauphin Island. The yellow arrow in each image points to the same feature. The view is looking west along Dauphin Island toward an inlet cut during Hurricane Katrina (Katrina Cut). The Gulf of Mexico is to the left. The linear rock structure that closes the Cut can be seen in the distance. Sand overwash deposits extend onto the road and farther in lobes toward the bayside of the island. Much of this overwash seems funneled through breaks in what appears to be human-made dunes. [larger version]

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pre- and post-storm photos
Location 2: Oblique aerial photographs of Dauphin Island. The yellow arrow in each image points to the same feature. Looking east toward the west end of Dauphin Island from over Katrina Cut. The Gulf of Mexico is to the right. Overwash sand filled the water bodies on the westernmost end of the island. Here, it appears the overwash extended across the island width and into the back bay. The gray colored material across Katrina Cut are rocks, or riprap, used to close the Cut. [larger version]

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pre- and post-storm photos
Location 3: Oblique aerial photographs of Dauphin Island. The yellow arrow in each image points to the same feature. The photograph is taken from over the Gulf of Mexico looking across the island toward the bay. This location is immediately west of Katrina Cut. Note the new breach. The surge and wave setup and runup overtopped the island and severed it, creating a new breach and leaving a classic overwash fan on the bayside. [larger version]

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pre- and post-storm photos
Location 4: Oblique aerial photographs of Dauphin Island. The yellow arrow in each image points to the same feature. The photographs are taken from over the Gulf of Mexico looking across the island toward the bay. Note the classic overwash fans extending the entire width of the island. (This westernmost part of Dauphin Island has been cutoff from the rest of the island by a breach initiated in 2004 by Hurricane Ivan and widened by Hurricane Katrina in 2005.) [larger version]

Chandeleur Islands, Lousiana

pre- and post-storm photos
Location 5: Oblique aerial photographs of Chandeleur Islands. The yellow arrow in each image points to the same feature. The view is looking west from over the Gulf of Mexico across the oil-protection berm in the pre-Isaac photo to a remnant part of the Chandeleur Islands (arrow). The berm in this area appears to have completely eroded during Isaac. [larger version]

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pre- and post-storm photos
Location 6: Oblique aerial photographs of Chandeleur Islands. The yellow arrow in each image points to the same feature. The view is looking west from over the Gulf of Mexico across the sandy oil-protection berm and/or island to a vegetated remnant part of the Chandeleur Islands (arrow). Like in Location 5, the sand berm-like feature seaward of the island remnant appears to have been completely eroded, leaving a shoal area where wave breaking is discernible (white lines). Some of these apparent changes may be due to water level differences between the times of the two acquisitions. Comparisons of pre- and post-storm elevation data will allow accurate vertical comparisons. [larger version]

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pre- and post-storm photos
Location 7: Oblique aerial photographs of Chandeleur Islands. The yellow arrow in each image points to the same feature. The view is looking west across the island from over the Gulf of Mexico. Some erosion of the Gulf shore is apparent here, but it is not as extreme as some other areas on the Chandeleurs. Sand is still apparent on the beach after the storm, unlike after Hurricane Katrina. [larger version]

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pre- and post-storm photos
Location 8: Oblique aerial photographs of Chandeleur Islands. The yellow arrow in each image points to the same feature. The view is looking west across the island from over the Gulf of Mexico. Sand evidently was driven landward as the Gulf shore significantly eroded. The remaining island was shaved narrower and vegetation was covered with sandy overwash deposits. [larger version]


St. Petersburg Coastal and Marine Science Center > Coastal Change Hazards: Hurricanes and Extreme Storms > Hurricane Isaac

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