GEOMORPHIC IMPACTS OF HURRICANES.

Meteorology: What is a hurricane?

A tropical cyclone: a cyclonic storm that originates in the tropics. Tropical cyclones typically form over large bodies of relatively warm water – tropical seas. They derive their energy through the evaporation of water from the ocean surface, which ultimately condenses into clouds and rain when moist air rises and cools.

Hurricanes are called typhoons in southeast Asia and cyclones in Australia.

A cyclonic storm has low pressure at the center and counter-clockwise rotating winds.

A tropical cyclone has winds > 74 mph (see Saffir-Simpson scale below).

A hurricane making landfall generates a storm surge that is greater on its right-front quadrant than its left-front quadrant, due to the counter-clockwise cyclonic circulation of winds.

Category  3-5 hurricanes generate storm surges typically of 3-5 m. 

 saffir

 Hurricanes can erode, transport and deposit sediment because of the combination of storm surge and large waves driven by strong winds. Given the origin and movement of hurricanes, the Gulf Coast and east coast are where landfalls occur in the U.S. Erosion: Erosion occurs where unconsolidated sediment (beaches, dunes) is subject to wave action. Erosion can cause scarping of a beach, destroying structures (houses, roads, etc.) and breaching barrier islands.

 
Assessing erosion: Pre and Post storm survey along transect lines:

 pre_and_post

 LIDAR (Light Detection and Ranging): the modern version of the old transect survey. A laser beam bounces from an aircraft to the ground within a wide swath, producing a very precise elevation map. This allows for before and after comparisons to evaluate erosion (reduced elevation) and deposition (increased elevation).

 Hurricane Deposition: Washover Deposition: washover fans and terraces are mostly sand deposits formed where waves overtop coastal barriers, such as beach berms and dunes. A fan is an isolated lobe-shaped deposit formed where waves overtop breaches in coastal barriers. A terrace is a continuous apron of deposition where waves overtop longer sections of coastlines. Fans and terraces were formed by Hurricane Irene along the U.S. east coast in 2011.

 Storm Surge Deposition: storm surge flooding may cover many tens of km inland and transport large amounts of offshore and littoral sediments into nearshore subaerial environments. The storm surge and wind-generated waves transport debris and sediment inland. A blanket of finer sediment deposited from suspension may extend far inland. Inland extent of sedimentation near High Island after Hurricane Ike was 3,567 m.

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