BARRIER ISLAND BARRIER ISLAND ROLLOVERROLLOVER

evidence for rollover see pp. evidence for rollover see pp. 24, 2624, 26

FACTORS INFLUENCING FACTORS INFLUENCING THE POSITION OF A THE POSITION OF A BARRIER ISLANDBARRIER ISLAND

• rate of sea level riserate of sea level rise

• sand supplysand supply

• sea energysea energy

• human interventionhuman intervention

SEA LEVEL RISESEA LEVEL RISE• Ice age glaciers retreated 15,000 years Ice age glaciers retreated 15,000 years

ago, sea levels rose- river valleys ago, sea levels rose- river valleys flooded- sediments from rivers were flooded- sediments from rivers were trapped-sand transported by wind/waves trapped-sand transported by wind/waves from oceanside to bayside- island from oceanside to bayside- island retreats inlandretreats inland

• sea level rise along the Atlantic Coast has sea level rise along the Atlantic Coast has been 1 ft/century - barrier island retreat been 1 ft/century - barrier island retreat 100-1,000 ft/ century see p 24100-1,000 ft/ century see p 24

SAND SUPPLYSAND SUPPLY

• with barrier island retreat sand with barrier island retreat sand buries backwater - marshes also buries backwater - marshes also retreat and are covered by forest, retreat and are covered by forest, then dunes , finally coastlinethen dunes , finally coastline

• longshore currents form spits longshore currents form spits through the deposition of sand through the deposition of sand

• see p. 17see p. 17

SEA ENERGYSEA ENERGY

• storms can break through inlets and storms can break through inlets and overwash, depositing sediments overwash, depositing sediments behind the islandbehind the island

• see p. 36see p. 36

HUMAN INTERVENTIONHUMAN INTERVENTION

• Ocean City Maryland plowed down Ocean City Maryland plowed down dunes to build high-rises - dunes dunes to build high-rises - dunes store sand, absorb wave energy- store sand, absorb wave energy- wave energy causes washover- sand wave energy causes washover- sand deposited in backwater areas deposited in backwater areas speeding up barrier island retreatspeeding up barrier island retreat

•dredging the offshore sands dredging the offshore sands

to replenish the beachfront to replenish the beachfront

•resulted in increased wave energy resulted in increased wave energy

on the on the shoreline as offshore sands

serve to buffer wave energy.

SUMMARYSUMMARY

• BARRIER ISLANDS ALONG THE BARRIER ISLANDS ALONG THE ATLANTIC COAST CONTINUE TO ATLANTIC COAST CONTINUE TO RETREAT TOWARD THE COASTLINE – RETREAT TOWARD THE COASTLINE – SW, IF SEA LEVEL RISE CONTINUES SW, IF SEA LEVEL RISE CONTINUES THE RETREAT WILL BE AMPLIFIEDTHE RETREAT WILL BE AMPLIFIED