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Coasts Part 2 Classifying Coasts/Beaches About 44% of the world’s population lives within approximately 93 miles of the ocean. Approximately 39% of the U.S. population lives in counties directly on the coastline. Coast & Shore • Coastal areas join land & sea • Shore = Place where ocean meets land (Ex. sandy beach) • Coast or Coastal zone = More than just the shore; It is the areas affected by the processes occurring at the ocean-land boundary (Ex. beach, dunes, marshes, cliffs, & offshore sandbars) Coast & Shore A coast is an active place! “There is nothing permanent except change” ~ Heraclitus 540-470 BC Coast & Shore Coasts can be affected by any of the following: •Breaking waves •Rise & fall of the tides •Discharge of river sediment into the ocean •Longshore currents •Ocean storms •Biological processes •Change in sea level •Sinking & rising of the land (tectonic processes) •Human activity Erosion & Deposition •Erosion is the process by which the Earth’s surface gets worn down. Erosion can be caused by wind, water, or ice. •Coastal erosion occurs along beaches and shorelines. •The process by which transported sediments are left in new locations is called deposition. Erosional Features Inlet: A narrow body of water between islands or leading inland from a larger body of water, often leading to an enclosed body of water , such as a sound, bay, lagoon, or marsh Bay Bay: A body of water partially enclosed by land, but with a wide mouth, giving access to the sea Inlet Erosional Features All three of these features are formed by wave erosion. Sea cave Sea arch Inlet Sea stack In order of increasing erosion… 1) Sea cave 2 1 2) Sea arch 3) Sea stack 3 Erosional Features Headland Sea Stack Sea cave Headland Sea arch Headland: A section of land jutting out into the sea, formed when different rocks erode at different rates Erosional Features Lagoon Lagoon: A shallow body of water that does not receive significant freshwater inflow and that is separated from the open ocean by a barrier island or coral reef Depositional Features Beach Depositional Features Sand dunes with vegetation/grasses Depositional Features Barrier island Mainland Lagoon or sound Barrier island Ocean Depositional Features Barrier island: A long, often narrow accumulation of sand that is separated from the mainland by open water (lagoon, bay, estuary) or by salt marshes Depositional Features Spit Depositional Features Spit: An extended stretch of beach material that projects out to sea & is joined to the mainland at one end Depositional Features Tombolo Depositional Features Tombolo: A spit connecting an island to the mainland Depositional Features Delta: Landform that is formed at the mouth of a river, where the river flows into an ocean, sea, estuary, or lake Review of Depositional Features Classifying Coasts Coasts can be classified as Primary or Secondary: Primary Coasts = Formed by terrestrial processes not related to the ocean (nonmarine processes); Owe their character & appearance to land erosion, deposition of sediments, & other processes that occur on land. Classifying Coasts Examples of primary coasts: •Volcanic coasts like Hawaii •Coasts shaped by earthquakes like Alaska, San Francisco •Coasts formed by land erosion when glaciers deposit sediment when ice melts •Coasts formed by land processes where sediment washes off the land to build out the coast (when rivers form deltas) •Wind deposition coasts with sand dunes •Land erosion coasts like Puget Sound & Chesapeake Bay, from drowned river valleys Primary Coasts Chesapeake Bay Delta Coast formed by glaciers Volcanic coast Classifying Coasts Secondary Coasts = Coasts significantly changed by wave action & other marine processes or marine organisms Classifying Coasts Examples of secondary coasts: •Coasts formed by biological activity (coral reefs, mangrove forests, oyster reefs) •Wave erosion coasts like the Pacific coast •Marine deposition coasts like sandy beaches & barrier islands Secondary Coasts Wave erosion coast Wave erosion coast Sandy beach Mangrove coast Some coasts can show characteristics of both primary and secondary coasts!!! Primary: Wind deposits sand to create dunes Secondary: sandy beach forms when waves deposit sediment Beaches A Beach is the most familiar feature of a secondary coast. A beach is a zone of loose particles that covers part or all of a shore. Beaches Water from waves washing onto a beach is called swash – carry particles onshore and increases beach slope. Water returning to the ocean is called backwash. If the water carries back the same amount of material as it delivered onto the beach, the beach slope will be in equilibrium & the beach will not become larger or smaller. Typical Beach Profile Typical Beach Profile Backshore = The zone of the beach above the high tide line Typical Beach Profile Nearshore = The zone that extends from the swash zone to the start of the offshore zone Typical Beach Profile Offshore = Extends seaward beyond the breaker zone to the edge of the continental shelf Typical Beach Profile Longshore or sand bar = submerged or exposed accumulations of sand lying parallel to the shore Typical Beach Profile Exposed sand bar at low tide Typical Beach Profile Surf zone = the section of the coastal zone between the coastline & the breaker zone Typical Beach Profile Breaker zone = the zone where waves begin to break References www.nasa.gov www.photolib.noaa.gov