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by Matthew Cimitile, Abby Sallenger, Hilary Stockdon, Karen Morgan, and Dennis Krohn, USGS

A series of before-and-after aerial photographs of North Carolina's Outer Banks shows the impact of Hurricane Irene on the coastline, highlighting several breaches that severed a state highway and moved large volumes of sand inland.

The series, produced by the U.S. Geological Survey (USGS) and posted online, features five photo pairs that show coastal change in areas from Cape Lookout to Oregon Inlet.

Hurricane Irene made direct landfall near Cape Lookout on August 27, 2011. Because of the right-angle shape of the Outer Banks, barrier islands facing southeast underwent different coastal changes than those facing east.

The southeast-facing coast, from Cape Lookout to Cape Hatteras, was exposed to waves and surge from the ocean. Photographs of Ocracoke Island (location 2 on map) show large volumes of sand removed from the beach system and deposited over roads and grass marshes. Flooding by storm surge in these areas was minimal, however, as surge crested above dunes only in limited places.

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The east-facing coast, from Cape Hatteras to Oregon Inlet, also was exposed to waves and surge from the ocean, but surge was higher in the sound. Sections of Rodanthe (location 4 on map) and Pea Island National Wildlife Refuge (location 5) were exposed to storm surge from Pamlico Sound of about 6 ft, which contributed to carving of channels through the island that breached a state highway in several places. A total of five breaches were cut through the coastal landscape between Cape Hatteras and Oregon Inlet.

"Such multiple breaches, or new inlets, cut through the Outer Banks could take weeks to months to close on their own," said USGS oceanographer Asbury (Abby) Sallenger, "and without intervention like pumping sand, some could even persist indefinitely, depending on the channel's cross section and the volume of water flushed through it on every tide."

Three days after the landfall of Hurricane Irene, USGS scientists acquired detailed information about coastal change through aerial photography and an airborne lidar (light detection and ranging) survey conducted with the National Oceanic and Atmospheric Administration. Airborne lidar is a remote-sensing tool attached to an aircraft that uses laser pulses to collect highly detailed ground-elevation data. Information from the surveys allows scientists to discern the degree of changes to beaches and coastal environments and to determine how much the land has eroded and where new inlets have cut through. The photographic and lidar information will be useful in mitigation and restoration efforts, such as rebuilding North Carolina Highway 12, which was severed in several places by breaches cut through the barrier islands by Hurricane Irene.

Data acquired will also be used to make more accurate predictive models of future coastal impacts from severe storms and to identify areas vulnerable to extreme coastal change.

View the before-and-after photographs illustrating coastal changes and damage from Hurricane Irene. Get more information on hurricane preparedness.