Offshore bars Barrier beaches and islands Origin and development of landforms and landscapes of coastal deposition Offshore bars Barrier beaches and islands

offshore bar - also called breakpoint bar or longshore bar

Offshore bars A ridge of sand lying parallel to the coastline Located offshore on the seaward side of the breaker zone (where waves first break ) so also called a breakpoint bar Semi-submerged by the tide - unlike barrier beaches and islands Formed from the sediment transported down the beach by backwash - therefore located at the lowest limit reached by the backwash of breaking waves (LWM = low water mark) May be more than one bar - the outer bar related to the breaking point of storm waves and the inner bar to normal waves Offshore bars are linked directly with the beach system unlike barrier beaches and islands

offshore bar - also called breakpoint bar or longshore bar

Barrier islands in Florida

Barrier islands in New York

Barrier beaches and islands An elongated sand or shingle bank which lies parallel to the coastline Not submerged by the tide even at high tide Separated from the mainland by a lagoon - lagoons also called sounds Separated by tidal inlets - creates a chain of offshore islands May have sand dunes behind the beach Saltmarsh (non-tropical coasts) or mangrove swamp (tropical coasts) may develop on fringes of lagoon Make up 10-15% of the world’s coastlines Barrier islands tend to migrate landwards - caused by washover or overtopping of material in storms - if they are pushed onshore they are transformed into barrier beaches

Barrier beaches and islands

Barrier beaches and islands Could be formed by the breaching of a spit in a storm or by strong river currents - the original sediment input would have been from headland erosion and longshore drift along the coast before the spit breached Could also have been formed by the landward movement of offshore sediments with the post-glacial sea level rise e.g. at Chesil Beach - constructive waves deposit sediment to form a barrier beach in front of the land Could simply be created by rising sea levels which flood the low lying land behind a beach and its sand dunes Barrier beaches and islands are typically found on low gradient coasts with a big supply of sediment (means a large beach can build up) and where the tidal range is low (means tidal currents are weak and do not interfere with deposition)

Barrier islands and beaches

Examples of barrier beaches and islands Eastern coast of the USA from Florida to New Jersey e.g. Cape Hatteras (N. Carolina), Long Island (New York) Chesil Beach, UK The Lido of Venice The Frisian Islands off the Netherlands and Germany

Eastern seaboard of the USA Cape Hatteras

Cape Hatteras

Venice Lido The Lido

The Venice Lido A sand bar along the Adriatic Sea coastline of N. Italy 11 km long One of two main barrier islands separating the Adriatic Sea from the mainland The salt water lagoon behind the barrier island is called the Laguna Veneta Venice is located on one of the islands in the lagoon behind The Venice Lido Lagoon largely enclosed by the barrier beaches - only three tidal inlets linking lagoon with the sea - results in very high variations in water level in the lagoon especially at spring tide - regularly floods Venice (the acqua alte or ‘high water’) Formed about 7,000-6,000 BP when breaking waves formed sand shoals offshore as sea levels were rising after the Ice Age

The Venice Lido

Frisian Islands The Frisian Islands

Frisian Islands A chain of islands stretching over 500km along the coasts of the Netherlands, Germany and Denmark in NW Europe Located between 5 and 30km off the mainland The West Frisian Islands (off the coast of the Netherlands) and the East Frisian Islands (off the coast of Germany) are barrier islands formed about 7,000-6,000 BP when breaking waves formed sand shoals offshore as sea levels were rising after the Ice Age Once specialised plants colonised the sand banks the sediment was stabilised and the barrier islands were formed The islands are continuously migrating from west to east as a result of wave action

Frisian Islands

Chesil Beach Chesil Beach

Chesil Beach

Homework task Compile a brief case study about the barrier islands linked with Long Island, New York. The information should be presented around a map(s). Include: Named barrier islands, beaches, tidal inlets and lagoons with facts/figures Recent physical change(s) linked with specific high energy weather events Key feature(s) of the human geography