Carolina Environmental Diversity Explorations

Hurricanes on sandy shorelines · By Dirk Frankenberg

Overwash fan on Masonboro Island

Mansonboro Island after Hurricane (Sand Lobes)

Figure 5. The overwash fan from Hurricane Floyd on Masonboro Island. (Photograph by the author. More about the photograph)

Figure 5 shows you some of the sand that was washed landward on Masonboro Island by hurricanes Dennis and Floyd. It was washed into and over the salt marsh, forming what geologists call an overwash fan. This structure forms like a river delta, in that water currents carry sand along until the water slows enough for it to drop out of suspension and onto the bottom. When the water recedes, the sand is left behind.

This overwash fan was deposited on what had been, before the hurricane, an intertidal salt marsh. It will take another event as extreme as Hurricane Floyd to move most of this sand somewhere else. Fine sand grains may be moved by wind to form dunes, but most of this sand will stay here, thereby making the island closer to the mainland than it was before the hurricane.

Definitions

salt marsh n.
A low coastal grassland frequently overflowed by the tide.
overwash fan n.
A break in a continuous dune line or line of vegetation where storm tides carried sand from oceanside, to estuaries, great ponds, and bayside; often clears a vegetation-free path from ocean to inner water body.
hurricane n.
A severe tropical cyclone originating in the equatorial regions of the Atlantic Ocean or Caribbean Sea or eastern regions of the Pacific Ocean, traveling north, northwest, or northeast from its point of origin, and usually involving heavy rains and has surface wind speeds greater than 74 miles (or 119 kilometers) per hour. [more]
intertidal adj.
Of or being the region between the high tide mark and the low tide mark.
dune n.
A hill or ridge of wind-blown sand.