Transcript for Hurricane Force - A Coastal Perspective, segment 10 of 12
About six months later, we were back in the area surveying the Mamala Bay off of Honolulu and Waikiki, and we took advantage of that opportunity to take the small boat we were working on over off of the south coast of Kauai where we saw most of the damage due to the hurricane and did some offshore surveys to see what the underwater effects of the hurricane were.
Questions about Iniki's impacts on the offshore bottom were motivated by sediment movements that occurred ten years earlier off the adjacent island of Oahu. In nineteen eighty-two Hurricane Iwa triggered submarine sediment flows which swept away current meters and severed interisland communications cables. Lacking indicators of change following Iniki, the scientists used side-scan sonar to create continuous ocean bottom images, the underwater equivalent of aerial photographs. Submarine channels and canyons show up readily on the images. While only limited evidence of hurricane-related change is apparent, the sonar images represent valuable baseline data for the future. Also collected was subbottom profiles which record sedimentary layers and bedrock beneath the ocean bottom. They reveal that large deposits of sand and other sediment, an important coastal resource, are filling the nearshore heads of the submarine canyons, poised to be moved to the offshore by a high-energy event such as a hurricane.
Locating and documenting the movements of this resource is of critical concern to developing island states and territories such as Hawaii, Guam, and Puerto Rico where scarce on-land supplies of sand and gravel, the main ingredient for roadbuilding and construction, are turning the search for these sediments to the offshore. On all hurricane-prone coasts the role of hurricanes in moving material throughout the coastal zone ties into a wide range of issues, from beach erosion and the movement of pollutants to the health of coastal ecosystems and the siting of development. All decisions concerning these codes must take into account that hurricanes will inevitably make landfall there in the future.
On a global scale there maybe tends to a few hundred tropical cyclones yearly. They aren't a rare phenomenon. They're practically a regular natural occurrence. At any one location they may be relatively rare, but over geologic time the cumulative effects of these storms will leave an imprint in the geologic record. A lot of the coastal plains, the low-lying areas of sand around islands, are often built up by these storms. In fact, you need storms like this to regenerate or resupply sediment to the coastal plains, and it's a natural process, an ongoing process, and the problems occur when human development conflicts with the natural process - in other words, building structures or houses in areas that are regularly, if not infrequently, impacted by these storms.