COASTLINES Aquatic Science coast: the zone extending from the ocean inland, as far as the environment is immediately affected by marine processes

Broad categories of coasts based on long period plate tectonic processes: 1. Pacific type (active): mountainous, close to plate collisions

2. Atlantic type (passive): mostly coastal plains instead of mountains, far away from plate collisions

Types of coasts based on short-term coastal dynamics: 1. Primary Coasts: formed by non-marine processes

Erosion coasts A. fjords: glaciers carve out land and it then floods with sea water B. drowned river valley: river flow erodes a valley that floods (Chesapeake Bay)

Sedimentation coasts A. delta: material carried by rivers flow into ocean, are deposited and accumulate in a triangular shape.

Volcanic coasts: coasts of Hawaiian islands Tectonic coasts (fault coasts): plate collisions push some of seafloor above water or a fault opens and ocean floods a new area

2. Secondary Coasts: formed and significantly changed by wave action and other marine processes. Wave-erosion coasts: pounding by waves wears away the coast A. Waves pound the coast, forcing water and air into cracks. Air in these cracks is compressed and then expands when the wave subsides. When the air re-expands, it can crack rocks, dislodge rock fragments, and enlarge fractures.

B. Abrasion: rocks hurled by waves and sediments in waves that have traveled hundreds of miles grinding and rounding rocks. These erosive forces can create certain features on secondary coasts Sea cliffs: steep cliffs caused by undercutting B. Sea caves: cut into areas of softer rock in sea cliffs and may develop “blow-holes” C. The irregular coast formed by erosion has bays (inlet/indentation in the shoreline) separated by headlands (points of land jutting into the ocean). These headlands get attacked from multiple sides because of wave refraction.

wave refraction: caused by waves approaching the shore at an angle. When they reach shallow water, the part of the wave nearest shore slows down first bending the wave. The rest of the wave moves at full speed and becomes parallel to the shore. Due to refraction, wave impact is concentrated against the sides and ends of headlands (the most protruding parts) and strike it from all 3 sides. Headlands become eroded to form offshore features such as: a. sea arches: formed by erosion of headlands (when two caves unite on opposite sides)

b. sea stacks: formed when arches fall, leaving isolated remnant of a headland c. shoreline straightening: when a coastline is straightened by erosion. A shoreline will straighten over time due to: - wave refraction (attacks anything protruding out) - deposition of sediment into bays

Marine-deposition coasts: when sea action causes ocean sediments to accumulate in one place If slope is steep, sediments will drain to deep water. If slope is not very steep, sediment will build beaches. Sediment is transported along the coast by wave and current action called longshore drift.

Beaches: zones of unconsolidated (loose) particles that cover part or all of a shore. Form when sediment (usually sand) is transported to a place suitable for deposition. Ex. calm spots between headlands, shores sheltered by offshore islands, etc. most familiar feature of secondary coasts landward limit: vegetation, seawall (built at shoreline to separate land from water), permanent dunes, or sea cliffs seaward limit: where sediment movement offshore ceases (depth approx. 33 feet)

E. composition and slope: composition of beaches can determine the shape. 1. smaller particles on beach = smaller slope. - The smaller particles interlock and do not allow water to percolate down. - Water rushes on the beach (swash), carrying particles and since no water percolates down, the same amount of water carries particles seaward during backwash. Result: gradual slope

2. Large particles do not fit together tightly, allowing water to drain beneath them. -On-rushing water disappears into the beach (less backwash to carry particles seaward). -The largest particles tend to build up along the back of the beach due to being thrown by large waves. Result: steeper slope The finer the particles, the flatter the beach.

Key features of a beach: berm: accumulation of sediments parallel to the shore, marking limit of sand deposition by wave action. Berm crest indicated by the marks left during most high tides. backshore: from berm to farthest point sand has been deposited = inactive part of beach with windblown dunes and grasses foreshore: seaward from berm and marks active zone of beach

Large-scale features of secondary coasts A. Sand spits: 1. most common feature 2. form where long shore current slows as it clears a headland and approaches a quiet bay 3. slower current in bay is unable to transport sediment, so sand and gravel are deposited in a line down current of a headland (often have a curve at the tip) B. Bay mouth bar: protects the bay from waves forms when a sand spit closes off a bay by attaching to a headland adjacent to the bay 2. inlet: the passage through the bay mouth C. Tombolo: a ridge of sand that connects an island to the mainland

D. Barrier Islands: 1. Ridges of sand that parallel the shoreline and extend above sea level 2. Mainly along Atlantic and Gulf coasts 3. Many are densely populated (Atlantic City, Miami Beach, Galveston) 4. separated from the mainland by a lagoon: long, shallow body of seawater isolated from the ocean 5. Originate in several ways: a. spits sever from mainland b. from old sand dunes that were on the shore during lower sea levels (ice age)

Coasts built by marine organisms: coasts that emerge due to biological activity Coral reefs B. Accumulation of oyster shells C. Marine plants that hold sediment and reduce force of waves Mangroves, sea grasses, etc.)

Human interference in coastal processes A. groins: a barrier built at a right angle to the beach to trap sand that is moving parallel to the shore B. breakwater: constructed parallel to the shoreline to create a calm water area to protect a marina. Result: too much sand accumulation and marina gets filled in. C. seawalls: massive barriers (granite), intended to prevent waves from reaching the areas behind the wall. Result: erosion on seaward side and total loss of the beach or collapse of the wall. D. jetties: to prevent a harbor or inlet from being blocked by deposition (to prevent formation of a baymouth bar)

Groin

Seawall

Jetties