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August 14, 2014 | By:  Sci Bytes
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Beach Erosion

By Ryan Hopkins

Trips to the beach have been a part of summertime tradition since the beginning of modern times. Americans have a particularly strong affinity for the ocean; an estimated 200 million people will visit U.S. beaches this year alone. The ocean and its cycle of waves and tides give a feeling of durability to coasts, but, around the world, the costly crisis of coastal erosion has taken hold. Many of the bunkers built by Germany as part of the WWII Atlantic Wall on the west coast of France were atop sand dunes in the 1940s; now, they're underwater during high tides. One million cubic meters of sand is lost from the coast of the Netherlands each year, a large concern for a country which is 30% below sea level. In America, areas of southwest Florida have seen the coastline recede over 200 feet since the 1980s.

The Earth's coasts have been in a constant state of evolution since the formation of the oceans. The slower geological processes that affect our shores are the same ones that shaped our continents. Volcanoes and earthquakes have the power to raise or lower land levels, determining the location and extent of coastlines. These are normally very slow changes, but we have had a few opportunities to witness some very quick transformations. The island of Surtsey formed in the northern Atlantic Ocean near Iceland as a result of a four year volcanic eruption from 1963 to 1967. The volcano rose from 426 feet below sea level to become an island of one square mile, giving a rare glimpse into the processes that can quickly form land from beneath the ocean. But as soon as the lava stopped flowing, the focus turned to erosion as the island started to disappear. The loose rock and sand on the edges of the island has washed away rapidly, leaving a core of tough and erosion resistant rock and reducing Surtsey to half its original area. In the 1989 Loma Prieta earthquake, large areas of the soil under San Francisco's Marina District liquefied, causing the complete destruction of many buildings, roads, and miles of coastline. Any surge of water caused by a storm or earthquake is going to carry with it a possibility of erosion. The 2004 tsunami presents an extreme example of coastal shift. Along the coast of Thailand, many areas experienced a one foot reduction in sand level while other areas found themselves swamped under several feet of sand and mud.

The catastrophic processes that raise or lower shorelines can cause large amounts of destruction very quickly, but when it comes to sheer magnitude, the slow but unrelenting assault of the ocean can't be matched. The shore receives the ocean's energy through waves, and though they may appear similar across the globe, they have a different effect at each coast they touch. Perhaps the strongest predictor of the waves' eroding effect is the topography of the ocean floor near the beach. Sand bars or large shoals will dissipate wave energy, as will significant "bumps" on the floor. These conditions can change rapidly, leading to an unexpectedly fast or slow rate of erosion.

The composition and shape of the shore also has a large effect on erosion. A sandy beach that gradually slopes out of the sea dissipates the wave's energy, while a cliff that rises out of the ocean without any sand or sediment at its base will be hit with the full force of the waves and forced to quickly retreat. The shore's can be equally important. Materials that resist transport and have a strong internal structure, like large volcanic rocks, slow erosion, while loosely packed sediment, such as the fine sand found along the coast of Florida, washes away quickly. Vegetation plays an dual role, with different types aiding or hindering erosion. Mangrove trees have sprawling root systems that can secure sand, while lichens can break down large, hard rock into pieces that can be swept out to sea.

Human activity has a dual role as well; man-made climate change has increased erosion on a global scale because of higher sea levels, but we also have the power to slow down and restore coasts which are receding. The strategy of managed realignment involves moving residents and businesses away from the rising water/receding shore and letting the ocean advance. This can be a cost-saving strategy when the eroding land is not very desirable and there are only a few residents to move. By contrast, the "hold the line" strategy keeps residents in their place and focuses on maintaining the current shorelines. This can be implemented with hard defenses,like seawalls, which are generally cheaper and easier to build than soft defenses, such as replenishing beaches with sand. Hard defenses currently protect 70% of Europe's shoreline. Counties in Florida have been spending millions annually on replenishing beaches which are critical to the state's multibillion dollar tourism industry. The "move seaward" and "limited intervention" strategies focus on building structures toward the ocean away from the current coast. Moving seaward, which involves building dunes or seawalls in a place that creates extra land and pushes the ocean back, is a very costly strategy, but it can reclaim coastal land and ecosystems which were victims of erosion. Limited intervention uses the natural features of the area to reduce erosion, such as encouraging and promoting wetland formation or barrier coral can reduce erosion of the higher valued coastline. Promoting wetland growth has been a large part of Louisiana's effort to protect New Orleans and other areas near the coast from storm surges and flooding. Climate change, rising sea levels and increased demand for valuable beaches and coastal areas are only raising the stakes in the continuing fight against the ever-encroaching ocean.

Graham, D., Sault, M., and Bailey, J. 2003, ‘National Ocean Service Shoreline - Past, Present and
Future', Journal of Coastal Research, 38, pp. 14-32.

M. Choowong. "Erosion and Deposition by the 2004 Indian Ocean Tsunami in Phuket and Phang-nga
Provinces, Thailand." Journal of Coastal Research 23.5 (2007): 1270-276. BioOne. Web. 8 Aug. 2014.

THOMASON, Jamie C. (2005). Beach Accretion And Erosion Caused by the Storm Surge of the September
2, 2004, Hurricane Frances on the Island of San Salvador, Bahamas, Salt Lake City Annual Meeting.

Turner, I.L., Leatherman, S.P. (1997). Beach Dewatering as a ‘Soft' Engineering Solution to Coastal
Erosion-A History and Critical Review. Journal of Coastal Research, 13 (4), 1050-1063.

University of Florida. Fewer Shark Attacks in 2013, Above-average Fatalities Worldwide. University of
Florida News. N.p., 17 Feb. 2014. Web.

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