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.
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:
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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