From National Geographic: Geography in the News: Storm Surge Threats
Superstorm Sandy sent a storm surge of 13 feet (4 m) onto New
Jersey’s and New York’s fragile shorelines, creating chaos and
widespread misery for coastal inhabitants. Examining experiences with
hurricanes Katrina and more recently Irene, storm surges clearly create
more damage than wind and rain during these tropical and middle latitude
Storm surges are associated with high winds over water. Wind over
open water can bring not only high water surging onto a shoreline, but
the surge, combined with intense wave action, can pummel shoreline
structures. Parts of demolished structures then become battering rams
with the surging water and waves destroying even more structures.
all ocean swells and waves are created by wind over water. As wind
speed increases, the height between the tops of swells and the troughs
that separate them increases. As the swells reach the shallow waters of
coastal areas, drag created at the bottoms of swells slows their
movement, creating breaking waves along the shore.
The faster the wind, the larger the body of water and the
longer the wind blows from a single direction, the larger will be the
swells. As these large swells approach the shallower water along the
shores, drag increases along their bottoms causing the tops of the
swells to become closer together. Thus, the net effect is that the water
literally piles up against the shore, creating a storm surge.
Therefore, hurricane-force winds blowing from the Atlantic Ocean
toward the Eastern Shore for several days can push a devastating storm
surge into low coastal areas, overwhelming natural protective dunes.
This process is precisely what happened with Superstorm Sandy between
Not since Hurricane Katrina struck the Louisiana and Mississippi
coasts in 2005 has there been greater coastal damage from a storm surge
than Sandy’s damage. Katrina was one of the top five deadliest Atlantic
hurricanes with a documented 1,833 dead. By far, the majority of
Katrina’s fatalities were caused by the storm surge that overtopped the
levies and flooded New Orleans’ low Ninth Ward. The protective dikes
were overwhelmed by the surge that reached 25 to 28 feet (7.6 to 8.5 m)
above normal sea level.
Additional factors played supporting roles in Superstorm Sandy’s
increased storm surge. As the counterclockwise rotating storm made
landfall on the New Jersey and New York coasts, the winds on the north
side of the storm came directly onshore driving the full force of the
surge onto the shoreline. In addition, the landfall coincided precisely
with the high tide associated with a full moon (spring tide). As the
moon lines up on the opposite side of the Earth from the sun during a
full moon (syzygy), the gravitational pull between the two intensifies, resulting in higher tides.
Few who endured the direct affects of coastal flooding associated
with Sandy’s storm surge will soon recover from the personal and
emotional damage. Storm surges, however, are the real destructive agents
and represent the most dangerous phenomena associated with tropical
Superstorm Sandy was a perfect example of the perfect storm, battering the densely populated East Coast with impunity.