Rapid Response: UM Team Studies Geologic Effects of Last Month’s Hurricane Irene on Bahamas
September 15, 2011
MIAMI — On August 25, 2011, Hurricane Irene passed over Exuma Sound and the Exuma Cays, Bahamas. The hurricane was a Category 3 storm with maximum sustained winds of 115 mph when it passed over the Exumas where the University of Miami (UM) has been doing extensive research, and operates a field station. Scientists from the UM Rosenstiel School of Marine & Atmospheric Science conducted a rapid assessment of the hurricane impact on the carbonate coastal systems from the storm’s center in the Exuma Cays to the outer bands of the storm on Andros, Joulters Cays, and Cat Cay.
Just days following the storm, Ph.D. student Kelly Jackson (MGG), M.S. student Kasey Cantwell (MAF), and Rosenstiel School Dean Roni Avissar boarded a helicopter from Miami to the Exumas to survey the effects of Hurricane Irene. More than 23,000 aerial photographs of the islands, coastlines, and shallow water environments document the immediate changes from the storm. Simultaneously, UM Marine Geology & Geophysics Professor Gregor Eberli and a group of Brazilian scientists onboard the R/V Coral Reef II recorded the effects of the storm from Bimini to Nassau.
Along the center path of the storm in the Exumas, the hurricane caused significant beach erosion, storm surge damaged vegetation, and sediment was suspended in a few shallow water environments along this 170 km long, 5-10 km wide island chain. Overall, no major changes to the coastal geomorphology occurred. For example, major channels remain unchanged and were still accessible by boat.
“As we flew over the affected area, we observed damage to the island’s vegetation and beach erosion but overall, no major changes to the landscape. The Exumas are a very large area and to ground-truth the islands and shallow-water environments would take weeks. Taking aerial photographs from a helicopter allowed us to assess a huge area in a matter of hours,” said Jackson, who has been working at this site for more than 3 years.
Away from the storm’s center, though still within storm-force winds, the Andros coastline and offshore reefs experienced very minimal damage. There were a few broken corals but overall no major damage to the ecosystem. The large subtidal ooid shoals of Joulters Cay and Cat Cay remained unchanged, however, at Joulters Cay, the storm surge formed a new beach ridge 1.2 m higher than the normal beach level. Storm surge flooded Andros Island and deposited a millimeter-thick layer of fine white mud on the mangroves and tidal flats. The waters on the leeward side of Andros were milk-white even 6 days after the storm due to the suspension of mud caused by the passing storm.
“Having this immediate aerial information and ship observations is important because it allows us to rapidly assess how hurricanes affect coastal systems. We know from working in the Bahamas that the daily tidal fluctuations will eventually minimize the effects of the storm. Therefore, it was essential to do a survey as quickly as possible to understand changes caused by the storm and create a benchmark so we can also observe how long it will take the coastal system to return to normal.” Eberli added. “Now, Dr. Pam Reid’s Coral Reef Imaging Laboratory will use the images to create mosaic photo panels of the region to compare to previous satellite images, so that we can truly understand the geologic impact of a Category 3 tropical cyclone on the islands and coastal system.”
About the University of Miami’s Rosenstiel
The University of Miami’s mission is to educate and nurture students, to create knowledge, and to provide service to our community and beyond. Committed to excellence and proud of the diversity of our University family, we strive to develop future leaders of our nation and the world. Founded in the 1940’s, the Rosenstiel School of Marine & Atmospheric Science has grown into one of the world’s premier marine and atmospheric research institutions. Offering dynamic interdisciplinary academics, the Rosenstiel School is dedicated to helping communities to better understand the planet, participating in the establishment of environmental policies, and aiding in the improvement of society and quality of life. For more information, please visit www.rsmas.miami.edu.