Title

Event sedimentation from Hurricane Andrew along the southwest Florida coast

Date of Award

1998

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine Geology and Geophysics

First Committee Member

Harold R. Wanless, Committee Chair

Abstract

Hurricane Andrew passed over south Florida on August 24, 1992 as a fast moving category 4 storm causing brief, but intense erosion and deposition. The sedimentary deposits created by Hurricane Andrew are of importance in that they represent the nature of the material eroded and transported during high energy events while also creating new source areas for sediment redistribution by subsequent prevailing winds, and winter storm waves and currents. The composition, thickness, and distribution of the hurricane deposits influence the future turbidity, nutrient levels, and oxygen levels in adjacent marine environments.The storm created four types of sediment deposits along the southwest Florida coast. (1) The onshore surge spread a broad, fine sand to mud layer across the supratidal and mangrove wetland. This layer covered over 110 km$\sp2$, was as much as 20 cm in thickness, averaged 8% in organic material, and was composed predominately of marine carbonate particles. (2) The flanks of channels and creeks contain ebb-surge deltas where as much as 2 meters of carbonate and organic-rich mud accumulated during and just following the hurricane. (3) Along the coast and interior bays and channels, some carbonate and organic-rich mud wedges and deltas formed during both the flood and ebb surge. (4) The brief but intense onshore surge caused landward migration of sand and shell behind beach ridges as much as 5-15 meters into the mangrove swamp.The study has monitored an organic-rich, quartz-carbonate, storm layer deposited across 450 square kilometers of the mangrove forest; storm deltas associated with channels and creeks; and mud wedges along the coast and interior bays. The sites have been subjected to bioturbation and forces of weather such as prolonged winter storms and tropical storms. After four years, all depositional sites preserve a relic of the Hurricane Andrew layer, though many have been altered. Throughout a four year monitoring period, the sites were studied quarterly for changes in sedimentary characteristics.Substrate elevation markers have showed an important aspect of the biological destruction which occurred when the hurricane swept through the mangrove forest. Because 60% of the mass of a mangrove tree is in the root system (Smith et al., 1994), mangrove root mass within the destruction zones have since been unable to re-establish themselves. At some stations, this lack of mature mangrove root-peat system has lead to a significant lowering or shrinking of the sediment and organic Holocene sediment package. At stations within impounded mangrove forests, as much as 2 cm per year reduction in substrate elevation has been recorded. Along the tidal rivers on the levees, the reduction in substrate elevation was approximately 1 cm per year.

Keywords

Geology; Physical Oceanography; Biology, Oceanography; Engineering, Marine and Ocean

Link to Full Text

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