Chapter 10COASTAL GEOGRAPHY AND WATERS

I. General Coastal GeographyA. shore: zone between high water mark and the lowest line where land has been

exposed; includes water and land territory1. offshore: zone beyond breakers; open ocean2. nearshore: zone between low tide mark and breaker line3. foreshore [intertidal zone]: zone between high and low tide4. backshore: division of shore only touched by water during storms or

abnormally high water; extends from high tide mark5. shoreline (water’s edge): boundary between water and land

6. breaker line: line where the farthest breakers touch bottomB. coast: extends from high shore boundary to any land still affected by marine

processes1. coastline: boundary between coast and shore

C. beach: entire active area of sediments affected by breakers; a sediment deposit in the shore area1. variables that affect erosion:

a. degree of exposure to oceanb. tidal rangec. composition of coastal bedrock

D. concordant coast: bands of differing rock types run parallel to coastE. discordant coast: bands of differing rock types run perpendicular to coast; leads to

development of headlands and baysF. eustatic change: global change in sea level caused by a change in the volume of

water present in the ocean or the ocean’s capacity1. sea level is lower during ice ages2. a mid-ocean ridge changes the ocean’s capacity

G. isostatic change: change in sea level relative to land caused by a tectonic activity in the continental crust that raises or lowers it

H. wintertime beach: beach with a thin berm, gently-sloped beach face, and well-defined longshore bar; swash does not soak into the beach due to heavy wave activity, so more backwash carries sediment down the slope

I. summertime beach: beach with wide berm, steep beach face, and no longshore bar; swash soaks into the sand due to light wave activity, so there is not much backwash to erode beach sand

II. Headlands and BaysA. headland: a piece of land extending from the shore surrounded by water on three

sides; found only on discordant coastlines; wave energy is concentrated on headlands due to refraction, which leads to the features seen below1. headlands are caused by erosion of the rock along the ocean; weaker rock,

such as sands and clays, are eroded by the sea and form bays and the stronger rock is not eroded nearly as much and becomes a headland

B. headland features (caused by wave refraction):1. sea caves: caves dug in the side of headlands due to concentrated wave energy2. sea arches: form when caves are drilled all the way through a headland and

openings are made on both sides3. sea stacks: vertical, tall, slender rocks formed by erosion of sea arches

a. sea stump: short sea stackC. types of headlands include:

1. peninsula: large headland2. cape: headland disruptive to a current3. promontory: long, narrow, and high headland

D. bay: body of water with land on three sides; wave energy is reduced here due to refraction1. pocket beach: beach formed between two headlands; doesn’t experience

longshore drift with other beach sections2. gulf: a large bay3. bight: a shallow bay

III. Beach FlowA. longshore currents: due to waves coming onto the beach at an angle, water moves

parallel to the beach; this leads to longshore drift, the transport of sediments parallel to the shore in the surf zone; can travel at 4 km/hr; most flow south along US coasts; these components lead to longshore currents/drift by vector addition:

1. swash: the water from breaking waves that travels up the beach parallel to wave motion

2. backwash: the water that travels directly down the beach slope due to gravitya. sheet flow: laminar movement of water away from the beach along the

bottom starting as backwashb. undertow: strong pull of water along the bottom away from shore due to

backwashB. beach flow types

1. swash-aligned: waves arrive perpendicular to shore and don’t transport sediment

2. drift-aligned: waves arrive at an angle and transport sediment parallel to shoreC. rip currents: strong, thin currents perpendicular to the shore caused by the

concentrated diversion of longshore currents at certain spots on the shore; usually not very long, have smaller waves, and look turbulent; speed can exceed 8 km/hr and is increased by:1. greater beach slope2. greater angle of breakers with beach3. greater wave height4. shorter wave period

IV. Primary and Secondary Coasts (Francis P. Shephard)A. primary coast: formed by non-marine processes; usually are young; include:

1. volcanic coast: contains igneous rock2. tectonically-formed coast3. alluvial plain: area around the mouth of a river, including the delta4. sediment deposition coast: contains sediment from land5. land erosion coasts6. river delta: rivers (land features) deposit sediment on the coast

B. secondary coast: formed by marine processes; usually are old; include:1. wave erosion coast (US Pacific Coast): beaches with higher wave activity tend

to have coarser/larger sedimentsa. armored beach: contains large rocks, which form lag deposits, which are

there because the beach is highly eroded; eventually, the large rocks protect the beach from further erosion

2. marine deposition coast (US Atlantic Coast): sandy beaches and spits3. biological (less common): mangrove coasts, coral reefs, marshes

V. depositional features: caused by the accretion and transport of sediment

A. spit: linear ridge of sand attached at one end to land; the other end points in direction of longshore drift; open end usually curves into a bay; formed by longshore drift

B. bay barrier: a spit may grow until it links up with land and completely encloses a bay

C. tombolo: a ridge of sand that connects an island to the mainland or an island to another island; caused by wave refraction, which diverts sediment deposition

D. barrier islands: long offshore deposits of sand lying parallel to the coast; common along US Atlantic coast; can be thin or wide; barrier islands along the US Atlantic coast are migrating landward due to relative sea level rise1. dunes: hills of sand on the shore formed by wind blowing dry sands; stabilized

by grasses2. barrier flat: flat area landward of the dunes3. salt marsh: biologically-productive area along the lagoon side of a barrier

island4. lagoon: water separating a barrier island from the mainland

E. key [cay]: a small, low, sandy island formed on or around a coral reef in tropical regions

F. moraine: deposit of sediment from a glacier that once reached the edge of the continent, then left sediment after it melted

G. river delta: flat, fertile area of sediment deposited by a river at its mouth1. distributary: small branching channel of water that distributes sediment onto a

deltaVI. Coastline Classification Based on Sea Level Change: sea level has risen 120 m since

the last ice age (18,000 years ago)A. Emergent Coast: coasts of this type have visible features that were previously

underwater; caused by the rising of a continent and/or a drop in sea level; characteristic of US Pacific coast due to thermal expansion of land1. causes

a. subduction of oceanic crust under continental crustb. glacial rebound: weight of ice is removed

2. marine terraces: series of adjacent beach berms, platforms, or benches on a beach caused by the relative sea level changing (due to tectonic, seasonal, or

tidal processes), which results in erosion and deposition to be concentrated at different heights on the beach; change in sea level exposes or submerges these terraces

3. wave-cut notch and wave-cut platform [bench]: water erodes part of a cliff and a notch forms at sea level; when the weight of the rock in the upper part of the cliff cannot be supported, it falls down and only a flat platform is left

4. stranded beach deposit: deposit of sediment well above sea levelB. Submergent [Drowned] Coast: coasts that were once high up, but are now closer

to sea level or below sea level due to a relative rise in sea level; characteristic of US Atlantic coast due to thermal contraction of land1. cause: tectonic activity2. relict beach: an area underwater that was once a beach3. estuaries (fjords, rias, coastal plain estuaries)

VII. Beach: system of sand set in motion by waves up to a depth of 10 meters off a coast; can be created or enlarged by deposition of sediments suspended in the ocean

A. features1. berm: raised section of gently-sloping sand just above the shoreline; formed

by deposition from wavesa. crest: a slight ridge running parallel to the shoreline; marks edge of bermb. face: slope leading from berm crest down to the ocean or to another berm

2. scarp: steep-sloped bank on the beach at the high tide water level where wave action erodes sand; occurs at the seaward edge of a berm

3. trough: depression separating a sand bar from the beach face4. longshore bar [sand bar]: slightly raised embankment formed below water

where waves first start to break; caused by deposition from wave action underwater

5. drift line: high point of where materials are deposited by waves on a beach

6. beach cusps: sorted deposits of different-sized sediment along the shore in arcs

B. beach slope1. gentle slope: fine-grained sand; occurs because swash cannot deposit sand

easily among densely-packed fine-grained sand particles already there2. steep slope: coarse sand; occurs because swash can deposit coarse sand easily

C. beach starvation: narrowing of beach due to erosion and disruption by man-made structures

D. beach replenishment/nourishment: addition of sand to a beach to replace lost sediment

E. beach sediment1. pink sand: Bahamas; comes from foraminiferans2. black sand: made of basalt, which comes from volcanoes3. quartz is the most common mineral composition of sand

F. Ninety Mile Beach, Australia (94 mi, 151 km): longest unbroken beachVIII. Coastal Waters

A. Characteristics1. Salinity is lower due to greater runoff and river input; however, this is slightly

counteracted by the dry winds passing over the continent and then evaporating large quantities of water on the coast, which raises salinity

2. Pollution concentrations are higher because pollutants are in water runoff3. Seasonal temperature change is greatest in the mid-latitudes4. Local geostrophic currents are on coasts and travel in the opposite direction

of the main currents; caused by the runoff veering right (in Northern Hemisphere) due to Coriolis effect; Davidson current is a big one on US Pacific coast

B. Coastal Lagoon: water separated from the ocean by a barrier island or spit; can be diluted by freshwater or hypersaline due to high evaporation1. Laguna Madre: hypersaline lagoon on the coast of Texas

C. Estuary: semi-enclosed coastal body of water in which the ocean water is diluted by freshwater from a river or runoff; the water is given the term brackish because it is brown and diluted; have high ecological productivity; bays, inlets, gulfs, lagoons, and sounds can be considered estuaries; most exist because of rising sea levels from glaciers melting in the past 18,000 yrs; water is generally isothermal in estuaries and near coasts1. Origin-Based Classifications

a. coastal plain estuary [drowned river valley, ria] (Chesapeake Bay): formed by ocean invading a river valley; wider distribution than fjordsi. Chesapeake Bay: largest estuary in the US

b. fjord [drowned glacial valley] (Puget Sound): U-shaped, steep-walled valley formed by glacial erosion that is filled with water; found in northern regions

c. bar-built estuary (Pamlico Sound): shallow estuary in a lagoon separated from the open ocean by a barrier island or other structure (spit, tombolo, bay barrier); these are common along the US Gulf and east coasts

d. tectonic estuary (San Francisco Bay): produced by faulting or folding of lithosphere; it is a depression in the land where ocean and river water mix

2. Water-Mixing Classificationsa. vertically mixed [well mixed]: vertically isohaline, shallow, low-volume

estuary; uniform salinity from top to bottom; salinity gradient is horizontal from head to mouth

b. slightly stratified: moderately shallow estuary containing two layers, the upper, less saline water from the river and the lower, salty water from the ocean; mixing still exists and a horizontal salinity gradient from head to mouth still exists

c. highly stratified: deep estuary in which the lower layer maintains a relatively constant ocean salinity from mouth to head, relatively undiluted by river input; the upper layer has a horizontal gradient from head to mouth; prominent halocline exists

d. salt wedge (Mississippi Estuary): forms near deep, large-volume rivers in which ocean water intrudes below the river water; prominent halocline near mouth; upper layer is evenly-mixed and fresh

3. entrainment: process of freshwater getting more salty as it mixes with ocean water

4. estuarine circulation pattern: net flow in stratified estuaries of low-salinity surface water toward ocean and high-salinity subsurface water toward shore

5. sill: underwater ridge of sediment in a fjord that partially blocks water flow in the estuary; forms by deposition from a glacier and is called a moraine above ground

D. Marginal Seas: large bodies of water connected to the ocean1. Mediterranean Sea: remnant of the ancient Tethys Sea separating Laurasia and

Gondwanaland

a. Mediterranean circulation: flow of ocean water into a marginal sea due to high evaporation within the sea; the water gets salty and goes back to the ocean as subsurface flow; this is the opposite of estuarine flow

b. about 6 million years ago, the Mediterranean dried up, but then took 100 years to fill back up with water at a later time

c. connects to the Atlantic Ocean by the Strait of Gibraltar; connects to the Black Sea by Bosporus Strait; Suez canal connects it to the Red Sea

d. Adriatic Sea: part of Mediterranean that is east of Italye. Aegean Sea: part of Mediterranean that is between Greece and Turkey

f. sill: underwater depositional ridge that separates parts of the Mediterranean

2. Gulf of Mexico3. Gulf of California: fed by rivers; opens toward south4. Bering Sea: located in the north Atlantic between Alaska, Russia, and the

Aleutian islands5. Red Sea: located by Indian Ocean between Asia and Africa; unusually salty

(maximum: 42.5 ppt)6. Arabian Sea: extension of Indian Ocean between India and Africa7. Bay of Bengal: located between India and other islands8. Weddell Sea: just above a section of Antarctica9. Black Sea: has anoxic water below 200 m due to a lack of mixing

IX. IceA. sea ice: permanent or nearly permanent ice covering high latitude waters due to

low temperatures; newly formed ice traps brine, which trickles out as the ice ages, because of saltwater exclusion (salt does not freeze in ice)1. pancake ice: small discs of ice

2. ice floes: sheets of ice on the open sea

3. pack ice: free-drifting ice not attached to the coast4. fast ice: ice fastened to the coast; >2 m thick

a. ice shelf (fast ice): thick sheets of ice over the ocean extending from continental glaciers, mostly in the Antarctici. Ross ice shelf: largestii. Larsen B ice shelf: disintegrated earlier in this century

B. icebergs: pieces of continental glaciers that have calved, or broken off, into the water; majority of their mass is submerged; RMS Titanic hit an iceberg and sank in 1912; Maxim Gorky, a soviet cruise ship, hit an iceberg in 1989, but nobody died1. castle berg: tall and thin2. tabular berg: large and flat

C. in the Arctic ocean, ice covers 3 to 6 million square miles (7 to 15 million square km) from summer to winter

D. polynyas: pools of water formed on ice sheets due to melting; create a positive feedback loop that amplifies the effects of global warming because their albedo is lower than that of ice

E. ice color1. white: has air bubbles trapped in the structure2. blue: densely packed ice that is mostly pure water

X. OtherA. fishing: 95% of fish is caught within 320 km (200 mi) of shoreB. beach compartment: collective region including a river, beach, and submarine

canyonC. coastal counties, accounting for 17% of the area of the continental US, have 53%

of the populationD. Law of the Sea

1. United Nations Conference on the Law of the Sea (Geneva, Switzerland): international meeting first held in Geneva, Switzerland; marine law was decided at this meeting; the most controversial policies are related to mineral mining rights

2. territorial sea: 12 mile wide zone around a country3. exclusive economic zone [EEZ]: 200-nautical-mile wide zone around a

country where the country has jurisdiction over marine resource use4. 42% of the oceans are controlled by individual nations

E. Amazon river: largest-volume river in the world; drains into South Atlantic from South America

F. coastal defenses1. flooding defense: dams and tidal barriers are built to prevent flooding

a. Deltaworks: Netherlands’ series of engineering projects built to protect the country from sea flooding

2. soft stabilization a. dredging [beach nourishment]: the movement of large masses of sand onto

the beach by humans, must be done to counteract erosionb. dune stabilization: grasses prevent erosion

3. hard stabilization: manmade structures built to prevent local erosion on the coast, but are actually harmful to natural sediment deposition processes, which leads to severe erosion on other parts of shore

a. jetty: barrier constructed to protect a harbor entrance; very harmful to natural sediment deposition processes

b. breakwater: a barrier or structure constructed near or on the shore to decrease energy of oncoming waves; protects harbors against strong waves; not excessively harmful, but may result in growth of the beach, which will require dredging if a calm area is still desiredi. tethered-float breakwater: floating buoy devices that decrease wave

energy, but do not disrupt sediment transportation negatively ii. rip-rap: rocks or other material used to armor and protect the shore

from erosion by absorbing the energy of wave impacts; typically made of granite or concrete rubble

c. groins: barriers perpendicular to the beach that are spaced in intervals with the goal of reducing local sediment loss by longshore drift; less destructive than jetties

d. seawall: structure built parallel to shore to protect beachfront properties; cause the most destruction of beaches because waves hitting the wall cause turbulence that carries away excessive amounts of sand