Sea-level anomalies affect beach erosion, but nobody has ever heard of them.


Onslow Beach, NC during a sea-level anomaly in 2009.

Sea-level anomalies are periods greater than 2 weeks when the water level at the beach is high.  They are not necessarily related to storm surge or sea-level rise, rather they are forced by changes in ocean currents.  On the US East Coast, slowing of the Gulf Stream or meteorological phenomena, like northeasterly winds or pressure changes, can pile water up against the shore and cause a sea-level anomaly.  They impact large stretches of coastline (e.g. Massachusetts to Florida) and occur every year, but some years they are more frequent.  Ethan Theuerkauf recently published a paper in Geophysical Research Letters that presents the first direct measures of the effects of sea-level anomalies on beaches.  He shows that a year with frequent sea-level anomalies can cause as much beach erosion as a year with a hurricane.  Compare Onslow Beach, NC during a sea-level anomaly, above, with Hurricane Arthur (July 3, 2014), below.  The hurricane made landfall at night, but you can still make out overwash (the camera is pointed landward across a washover fan).

About Antonio Rodriguez

Institute of Marine Sciences
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