Fisher, J. Barrier island formation: discussion. Geological Society of America Bulletin , 79 , — Gilbert, G. The topographic features of lake shores. Geological Survey 5th Annual Report, pp. Hayes, M. Barrier island morphology as a function of wave and tide regime. In Leatherman, S. Lawrence to the Gulf of Mexico. New York: Academic Press, pp. Hoyt, J. Barrier island formation. Geological Society of America Bulletin , 78 9 , — Leatherman, S.
Barrier Islands from the Gulf of St. New York: Academic Press. Monticello, IL: Vance Bibliographies. Public Administration Series: Bibliography. Masetti, R. Application of a barrier island translation model to the millennial-scale evolution of Sand Key, Florida.
Continental Shelf Research , 28 , — McGee, W. Encroachments of the sea. In Metcalf, L. Moore, L. Complexities in barrier island response to sea level rise: insights from numerical model experiments, North Carolina Outer Banks.
Journal of Geophysical Research , , F, doi Oertel, G. The barrier island system. Marine Geology , 63 , 1— Otvos, E. Barrier island formation through nearshore aggradation-stratigraphic and field evidence. Marine Geology , 43 , — Pilkey, O. Global distribution and geomorphology of fetch-limited barrier islands.
The natural pattern has a substantial impact on development potential, and on the cost of protecting such development. Sand moves; roads and houses are inflexible.
As described by the Department of the Interior in The islands are made up of unconsolidated and shifting sands. The continually changing relationship between the ocean floor, surf line and moving sediment, produces islands that are, for the most part, structurally and locationally unstable Permanent human habitation on many of these islands is hazardous for a number of reasons.
First, sea level is slowly but steadily rising, averaging about one foot per century along the mid-Atlantic coast. Secondly, the unconsolidated sand routinely moves about while the works of man require stability. Erosion, or migration, rates are high. Lands now considered safe for building may be extremely hazardous or may simply disappear within a few years. Thirdly, the islands are vulnerable to hurricanes and other storms.
Storm waves breach and overwash the dunes and entire sections of an island can be inundated or severely eroded. Most of the barrier islands are The development of these resources has often been encouraged by federally permitted or subsidized roads, bridges, and sewers, with the result that millions of people have been subjected to the hazards of hurricanes, and to property losses from the erosion and other physical changes that are characteristic to barrier formations.
These hazards and losses have, in turn, invited substantial Federal spending for seawalls.. In the United States, people are moving to barrier islands despite the risks. On barrier islands, population densities are three times the density of the coastal states on average. Major development has already occurred on barrier islands in the Town of Chincoteague and the City of Virginia Beach. In addition, the Federal government has developed Wallops Island for launching rockets.
The Nature Conservancy acquired its holdings in anticipation of "flipping" the real estate, reselling the islands to a Federal agency for permanent protection. When economics and politics delayed such a sale, the organization invested even more heavily to preserve the shoreline by acquiring farmland and forests on the Eastern Shore. The Volgeneau Virginia Coast Reserve now includes: Stopping the short-term profits associated with new resorts and industrial-scale tourism was not popular in local development or political circles.
The owners of Metompkin Island refused to sell it to The Nature Conservancy at any price, seeking instead to boost the economy by selling the island to a development firm call Offshore Islands, Inc. However, the acquisition-savvy conservancy had simply created a dummy corporation, and ended up purchasing the island in disguise.
Sandbridge, a beachfront home community built on a barrier island near Back Bay Wildlife Refuge, is at risk of washing away. A public policy issue in Virginia Beach is who should pay to replenish the sand to protect private property , an issue that is also a factor for the resort hotel strip further north in Virginia Beach. Federal subsidies for sand nourishment projects are welcomed by local officials, but taxpayer advocates question the rationale of borrowing funds at the national level to provide highly-localized benefits.
When sand accumulates in the yards of local residents, threatening to cover patios and pools, the homeowners struggle with state requirements to obtain a permit from the Virginia Beach Wetlands Board to move the sand back onto the public beach area. The homeowners do not need any permit to haul the sand away, but replacing it on the beach is not permitted without approval.
After the Wetlands Board fined two homeowners who moved sand drifts from their property to the public beach, the Sandbridge community requested an emergency declaration from the City Council to authorize sand transfers.
Inlets on barrier islands open during major storms, then silt in and close up over time. In the 's, English ships bringing colonists to Roanoke Island encountered a dozen inlets cutting through the barrier islands.
That led to erosion of as much as 2, feet from the northern end of Roanoke Island, perhaps destroying the site where the "Lost Colony" was established in In , a hurricane breached Assateague Island, carving an inlet from the ocean to Sinepuxent Bay. The U.
Army Corps of Engineers quickly locked the inlet in place by building a jetty on the north edge, blocking sand transport that would have naturally closed up the inlet. Ocean City then developed as a fishing port and ultimately a beach resort. After another storm in , plans for resort-scale development on Assateague Island were dropped and the National Park Service acquired most of the land for a national seashore.
That stopped most new residential and commercial construction, but the Federal government agreed to maintain the inlet. The Ocean City Inlet has been kept open by jetties and by dredging of the channel, and those artificial barriers have blocked sand from drifting southward and renewing the southern part of Assateague Island. The normal flow of sand, now trapped by the jetty, has created a wide beach on the northern part of the island.
South of the inlet, there has been extensive erosion from the barrier island, no longer resupplied with sand by longshore currents. Without natural replenishment, the barrier island just south of the inlet has shrunk and migrated westward substantially. Sand from the longshore currents still flows to Virginia, ending up at Toms Cove near Chincoteague. That portion of Assateague Island is still growing accreting , extending the southern end of the island and creating a sandbar "hook.
According to the US Geological Survey, the pattern of changing ocean currents has shaped the shoreline: The relatively abrupt transition at Chincoteague Inlet marks the boundary between the wave-dominated islands to the north and the mixed-energy, "drumstick" islands with large ebb-tidal deltas to the south The southern section of Wallops Island, which is the most stable island of the group, retreated about m from to for an average rate of 2.
The present surfaces of Assawoman and Metompkin Islands are extremely low, and are essentially an amalgamation of thin overwash fans migrating across the back-barrier marsh. It is often difficult to define the shoreline of either island on aerial photographs. In other words, because of sediment starvation and rapid transgression, at times these barrier islands essentially cease to exist.
To maintain its tourism-based economy, the Town of Chincoteague has expressed its preference for perpetual Federal maintenance of the bridge from Chincoteague Island to Assateague Island and recreational facilities on Assateague, so people can drive their own vehicles to the ocean shore for fishing, swimming, and sunbathing.
Fighting natural shoreline processes at the wildlife refuge is both against Federal policy and too expensive. The CCP proposal continues a long-standing Federal policy at Assateague National Seashore, articulated by a senior Department of the Interior official back in Contrary to the belief of many It would be folly to attempt to halt their migration.
Consequently, the construction of permanent facilities which parallel the shoreline Any construction on a barrier island is at risk of being eroded away, or shifted inland as the beach expands.
The Assateague Island lighthouse in Maryland was built in next to the ocean shoreline, but today that site is almost two miles inland. Along the Eastern Shore, the Virginia islands themselves are so low they are at risk of complete inundation in a northeaster or hurricane. In an storm, only the high ridges of Smith Island remained above water, providing shelter among the pine trees to cattle and sheep.
Everything on a barrier island is subject to change. Overwash during storms is a normal process, absorbing the storm energy and redistributing the sand inland. Tree stumps from forests that once grew on the bay side of barrier islands are occasionally exposed on the ocean side, showing the migration of the beaches to the west after years of big storms.
On Hog Island, the northern part erodes when the southern part grows accretes , but the cycle shifts after roughly years. In the 's, residents of the Broadwater community and the rest of Hog Island moved to Willis Wharf. The former location of Broadwater is now underwater. Virginia's barrier islands may be changing their shapes in three different patterns. Wallops, Assawoman, Metompkin, and Cedar islands between Assateague and Parramore are starved for sand replenishment and retreating westward steadily as sea level rises.
Further south, Parramore, Hog, Cobb, and Wreck islands are rotating. The southern group, including Ship Shoal, Myrtle, Smith, and Fisherman's islands, are developing straighter shorelines as they move westward.
Fisherman's Island is growing rapidly, from thirty-three acres in to over 1, acres today. Sediments have been derived from both sides of the Delmarva Peninsula. In the 's, the Cape Charles paleochannel was blocked by accumulating sediments at Wise Point, as currents from the bay and Atlantic Ocean shoreface created a sand bar on the bottom that built upward until it emerged and grew over years.
The western Chesapeake Bay side of Fisherman's Island and the middle section known as "The Isaacs" formed, then merged with each other and the ancestral core of Adams Island to create the current Fisherman's Island.
Between Assateague and Fisherman's islands, all barrier islands on Virginia's Eastern Shore are migrating towards the west. As sea level rises, the islands are "rolling over" as sand is eroded from the ocean side and redeposited on the bay side during storms.
Climate change has contributed to erosion, by allowing the wax myrtle shrub Morella cerifera to survive through more winters. The shrub has out-competed the grasses responsible for building sand dunes.
Researchers working through the Virginia Coast Reserve Long-Term Ecological Research project concluded in that barrier islands covered with a shrub forest, rather than sand dunes, are more susceptible to permanent erosion during major storms. They noted: The explosion of Morella on Cobb Island led to so much erosion that a nor'easter in the [] spring breached the island, essentially splitting it in two. Over that period, shrub cover expanded to roughly 40 percent of the landscape It's an abrupt change that occurs and it's irreversible We have some plots where we actually cut out the shrubs.
We look at what comes back after we removed the shrubs and it's not the same system. So it's an irreversible change in the system. The Corps of Engineers dredges the Chincoteague Inlet annually to maintain boat access, and dumps the spoil pile off Wallops Island to help protect that shoreline from erosion by major storms. Photograph by Patty Bodwell , My Shot. Marsh Arabs The Madan, or Basra Marsh dwellers of southern Iraq, are thought by some historians to be descendants of the ancient Sumerian civilization.
These so-called "Marsh Arabs" have lived for millennia by fishing and grazing buffalo in the lush delta of the Tigris and Euphrates Rivers. Adapting to the ebb and flow of the tide, the marsh dwellers reside in floating reed houses and transport themselves in boats and canoes.
Unfortunately, the marshes were reduced drastically during the presidency of Saddam Hussein. The number of Marsh Arabs in Iraq shrunk from about , to as few as 20, Today, the Madan find it difficult to maintain a livelihood as the polluted, drained, and saline waters of the marshes cannot support enough commercially viable wildlife.
Also called industrial agriculture. Also called an alpha predator or top predator. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region. Birth, growth, and death usually characterize the life cycle of animals. Usually rivers enter another body of water at their mouths.
Pesticides can be fungicides which kill harmful fungi , insecticides which kill harmful insects , herbicides which kill harmful plants , or rodenticides which kill harmful rodents. Also called a storm tide. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. A biome is an area classified according to the species that live in that location. Temperature range, soil type, and the amount of light and water are unique to a particular place and form the niches for specific species allowing scientists to define the biome.
However, scientists disagree on how many biomes exist. Some count six forest, grassland, freshwater, marine, desert, and tundra , others eight separating two types of forests and adding tropical savannah , and still others are more specific and count as many as 11 biomes. Use these resources to teach middle school students about biomes around the world.
Marine ecosystems contain a diverse array of living organisms and abiotic processes. From massive marine mammals like whales to the tiny krill that form the bottom of the food chain, all life in the ocean is interconnected. While the ocean seems vast and unending, it is, in fact, finite; as the climate continues to change, we are learning more about those limits. Explore these resources to teach students about marine organisms, their relationship with one another, and with their environment.
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Grasses dominate marshy ecosystems. Also called water level. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Text Text on this page is printable and can be used according to our Terms of Service.
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