The Coast

The Coast The coasts of the world’s continents are the most populated areas on the planet.

The Coast Two general types of coast. 1. Passive coast= far from lithospheric plate boundary with very little tectonic activity

The Coast 2. Active coast = near lithospheric plate boundary with a lot of tectonic activity

Coastal Zone Include the open coast as well as the semi-isolated and sheltered bays and estuaries Boundary defined by ocean features and therefore can vary greatly in distance from the shore.

Coastal Area These are regions of change in which the sea acts to alter the shape and configuration of the land. Changes can be extreme and rapid (eg. Hurricane)

Coastal Area Can be subtle and slow (eg. Mississippi River Delta)

The Shore The Shore is the area between low tide and the highest point affected by storm waves. This upper boundary is known as the coastline (highest point affected by storm waves).

Beaches The Area is an accumulation of sediment (sand or gravel) that occupies a portion of the shore. The beach is not static, but moving and dynamic.

Sandy Beaches Sandy Beaches are characterized by large sandy shores with no large rock or boulders.

Sandy Beaches Sand comes from local sources and can vary greatly in texture and color (white, tan, black, silt, etc.)

Rocky Beaches Shore line consisting of large boulders and rocks, with minimal sandy surface.

Estuaries The mouth of a river, bay or lagoon. This is where fresh and salt water mix. Salinity of the estuary is affected by the tides.

Marshes An area of soft wet land. Flat land periodically flooded by salt water. Common in portions of lagoons.

Cliffs A steep vertical rockface at the edge of the sea or at the back of a beach.

Dunes Coastal deposit of sand lying landward of the beach. Gets sand from onshore winds that transport it inland.

Fjords A long, narrow, deep, U-shaped inlet that usually represents the seaward end of a glacial valley that has become partially submerged after the melting of a glacier.

How sand moves

Sand movement Sand moves both parallel and perpendicular to the shore.

Mechanisms of Perpendicular movement 2 main mechanism of perpendicular movement. 1. Swash- Water that soaks into the beach leads to deposit of sand. 2. Backwash- Water that flows back to the ocean. Leads to erosion of sand.

Summer vs Winter beaches In summer – light wave activity means swash dominates over backwash = large well developed berm

Summer vs. Winter beaches In Winter- High wave activity- Backwash dominates swash = sand moved down the beach (erosion) to form longshore bars.

Parallel movement Longshore current – Waves hit shore at slight angle then return straight back to the water- zig zag. This current can carry swimmers down the beach.

Parallel Movement Longshore Drift- The zig zag movement of setiment (sand) by the longshore current. Only affects surf zone. This “river of sand” typically flows South along both Atlantic and Pacific American shores.

Erosional vs Depositional Shores Erosional shore- Have well developed cliffs. Are in areas of tectonic uplift (eg. Pacific coast) Depositional shore- Sand deposits and offshore barrier islands are common. (eg. S.E. Atlantic coast).

Erosional Shores Do to wave energy headlands are carved into cliffs, sea arches, sea stacks and marine terraces.

Erosional Shores Sea Arch

Erosional Shores Sea Stack

Erosional Shores Headland

Depositional shores Lonshore drift and other forces create an array of features on depositional shores. They include, A spit, tombolo, Barrier Island, Deltas and Beach compartments.

Depositional shore features A Spit- An arching ridge of sand extending from the beach into the ocean.

Depositional shore features Tombolo – sand ridge connecting island to mainland.

Depositional shore features Barrier Islands – long, narrow, sedimentary islands running parallel to the shore. Their features include Ocean beach, dunes, barrier flat, high salt marsh, low salt marsh and lagoon. Figure10.10a

Depositional shore features Deltas – Formed at the mouth of a river by heavy sediment. Can form a “bird foot” like structure.

Depositional shore features Beach compartments- Sections of beach with thin sand deposit at the north widening as it moves south until it reaches an offshore submarine canyon. Created by 1. Sediment delivered from a rivers, longshore drift (moving sediment south) and a submarine canyon at the south (funneling sand out to sea). Fig. 10.12

Depositional Shore

Depositional shore features Beach starvation- caused by human interference with sediment (damming or altering rivers). Depletes and often destroys beaches (sand still leaves through submarine canyons).

Emerging and submerging shorelines. Shorelines can be defined by relation to sea level through time. -Shorelines that are rising are called Emerging shorelines.

-Shorelines that are sinking are called Submerging shorelines.

Features of Emerging shorelines. -Marine terraces are flat platforms backed by cliffs. These platforms show ancient sea levels. -Stranded beach deposits – marine fossils found above current sea level.

Features of Submerging shorelines - Drowned beaches, submerged dune topography and drowned river valleys.

What causes change in sea level? I. Movement of earths Crust A. Tectonic movement- US Pacific coast emerging due to subduction of plate boundary off shore (think back). US Atlantic coast- submerging- Why?________________________

B. Isostatic movements- 1. Isostacy is essentially bouyancy B. Isostatic movements- 1. Isostacy is essentially bouyancy. How could you make something floating (like a continent above the mantle) sink by a few feet?____________________________

II. Worldwide changes in sea level (Eustatic) II. Worldwide changes in sea level (Eustatic). This is either do to having more sea water (eg. Melted sea ice) or having a smaller or larger ocean basin (the bowl gets smaller or larger).

US Coasts I. Atlantic (Tell me to cue up google earth) Barrier islands from Massachusetts southward (protect coast from storm waves) Bedrock in Florida is limestone, bedrock N. to N.J. is crumbly sedimentary rock = these provide material for barrier islands further south.

-North Atlantic shores were formed by glacial deposits left after melting. -North Atlantic shores are affected by storms called nor’easters blown in from N. E. seas - Atlantic coast eroding about 2.6ft per year.

II. Gulf Coast -Mississippi river delta is a major feature in the Gulf II. Gulf Coast -Mississippi river delta is a major feature in the Gulf. (go to google earth) - Gulf coast eroding at 6ft per year (14 ft at Mississippi river delta) -Passive shores with many depositional features (barrier islands, spits, tombolo, mudflats etc.)

Pacific Coast -Tectonically rising -Many cliffs, terraces, outcrops and other erosional and emergant features. -Storm waves (sometimes 20ft tall) erode sands in winter and deposit sand in summer.

-Damming rivers has caused Beach Starvation on many Pacific beaches.

Hard Stabilazation Hard stabilization includes all human built structures meant to stop/change the flow of sand.

Groins- structures perpendicular to the shore that are intended to stop the flow of sand. Built of Rip-Rap – large blocky material. -multiple grions in a row are called a groin field.

B. Jetties – like groins but built on both sides of a harbor.

C. Sea walls – “fail” attempt to protect coastline C. Sea walls – “fail” attempt to protect coastline. Run along and parallel to shore line. Cause collapses and violent destruction.