Chapter 12 - Coasts

Notes Complete Garrison Complete

Coast

the zone extending from the ocean inland as far as the environment is immediately affected by marine processes

Shore

the place where ocean meets land; on nautical charts, the limit of high tides

440,000

The world ocean is bounded by about _____ km of shore:

Location

The _____ of a coast depended on global tectonic activity and ocean water volume:

Shape

The _____ of a coast is the product of uplift, subsidence, erosion, and deposition:

Erosion

a process of being gradually worn away

Active Coasts

_____ are present along the leading edge of a moving continent:

Passive Coasts

_____ are present along the trailing edge of a moving continent:

Tectonic activity

The influence of _____ is obscured by wave action, erosion, and deposition regarding coasts

Eustatic Change

a worldwide change in sea level, as distinct from local changes

Glacial/warming events cause low/high sea level

The container space of the ocean varies with subduction and spreading

Expansion/contraction of volume of water at differing temperatures

Three factors of eustatic change:

Tectonic motions and Isostatic adjustment

Atmospheric conditions like winds and storm surges, as well as seiches

Two factors of local sea level change:

2,500

Sea level at its current elevation has only been present for about _____ years:

18,000

The most recent sea level low point occurred _____ years ago in a glacial event:

+6 ; -125

Sea level has varied from _____ m to _____ m relative to present level:

Erosional Coast

a coast in which erosive processes exceed depositional ones

Depositional Coast

a coast in which processes that deposit sediment exceed erosive processes

Depositional ; Erosional

About 30% of US coasts are _____ and 70% _____ :

Hydraulic pressure

_____ from wave action slowly weakens and erodes rocks:

Sediment

_____ carried by waves erodes rock relatively quickly:

Rock hardness/resistance ; Wave violence ; Tidal range

The rate of shore erosion dependent on _____ , _____ , and _____ :

Granite/basalt

Coasts made of _____ erode very slowly, at about a few cm/decade:

Soft or soluble material

Coasts made of _____ may erode a few m/year:

High Energy Coast

a coast exposed to large waves

Low Energy Coast

a coast only rarely exposed to large waves

Fetch ; Eastern

High energy coasts are commonly adjacent to areas with large _____ along the _____ edge of continents:

British Columbia, Maine, southern tips of South America and South Africa

Typical high energy coasts:

Gulf of Mexico

Typical low energy coasts:

Quickly

A shore with little tidal variation erodes _____ because energy is concentrated in one area:

Sea Cliff

a cliff marking the landward limit of marine erosion on an erosional coast

Sea Cave

a cave near sea level in a sea cliff cut by processes of marine erosion

Wave-Cut Platform

the smooth, level terrace sometimes found on erosional coasts that marks the submerged limit of rapid marine erosion

Sea Arch

an offshore feature of rocky coast, where a sea cave has worn through a rock face

Sea Stack

an offshore feature of rocky coasts of towering rock not yet eroded

Shore Straightening

the process where waves erode an early coast based on differing degrees of rock hardness, then focuses energy on exposed headlands through wave refraction

high-energy coasts

Shore straightening occurs most rapidly on:

Fjord

a deep, narrow estuary in a valley originally cut by a glacier

valleys eroded by rivers and/or glaciers which have been flooded by changing sea level

Coasts can be shaped by land erosion when:

island-forming magma

Many island coasts are initially formed by:

a steep escarpment forms

When the seaward side of a coastal fault moves downward:

undercut notches

The steepness of a sea cliff is a result from the collapse of:

sea cliffs

The position of _____ marks the shoreward limit of marine erosion:

blowhole

A _____ forms when erosion follows a zone of weakness upward to the top of the cliff

Sediment

_____ is transported from headlands to beaches during shore straightening

Volcanic and tectonic

_____ activity changes the shape of coasts:

Fault coasts

_____ occurs where seawater intrudes shifting land transformed by faults:

Depositional coasts

Features of _____ are consistent of sediment rather than rock:

erosional processes

A layer of protective sediments insulates underlying rock from:

depositional coast

Without any interference, an erosional coast will develop into a _____ over time:

Beach

a zone of unconsolidated particles extending from below the water level to the edge of the coastal zone

vegetation, sea cliffs, dunes, seawall

The landward limit of a beach could be:

onshore and offshore sediment movement

The seaward limit of a beach is where _____ ends, about 10 m deep

Beaches

_____ are in a constant state of change:

headlands, offshore islands ; surf ; broad high energy coasts

Beaches result from calm spots sheltered by _____ or from areas with moderate _____ or _____

Beach composition

_____ ranges from boulder → cobble → pebble → gravel → sand → silt:

finer

The _____ the grain of beach particle, the lesser the slope:

Swash

water from waves washing onto a beach

Backwash

water returning to the ocean from waves washing onto a beach

equilibrium

An equal among of swash and backwash transition keeps a beach in:

Fine-grain

_____ beaches are gradually sloped because water has a difficult time percolating into the beach itself to carry away sediment to create a slope:

Coarse-grain

_____ beaches are steeply sloped because water can easily percolate into the beach itself, where it carries away sediment, creating a slope

Berm

a nearly horizontal accumulation of sediment parallel to shore; marks the normal limit of sand deposition by wave action

Berm Crest

the top of the berm; the highest point on most beaches; corresponds to the shoreward limit of wave action during most high tides

Backshore

sand on the shoreward side of the berm crest, sloping away from the ocean

Foreshore

sand on the seaward side of the berm, sloping toward the ocean, to the low-tide mark

berm crest

The _____ corresponds to the highest point of the beach with vegetation and sand dunes:

inactive

The backshore is an _____ region of the beach with vegetation and sand dunes:

Beach Scarp

a vertical wall of variable height marking the landward limit of the most recent high tides; corresponds with the berm at extreme high tides

Longshore Bar

a submerged or exposed line of sand lying parallel to shore and accumulated by wave action

Longshore Trough

submerged excavation parallel to shore adjacent to an exposed sandy beach; caused by the turbulence of water returning to the ocean after each wave

Sandbar

a submerged or exposed line of sand accumulated by wave action

Large storms, waves, tides

_____ change sediment structure of beaches:

winter

Large waves are associated with _____ months:

winter

Beaches are cut to a lower level during the:

Nearshore

the region of ocean closest to land, through the zone of breakers

Offshore

the region of ocean past the area of breaking waves

Ripples

caused by the rushing currents on sand

Rills

small, branching surface depressions that channel water back to the ocean from a saturated beach in falling tide

Backwash Marks

diamond-shaped marks form when projecting shells, pebbles, or animals interrupt backwash

Low-Tide Terrace

the smooth, hard-packed beach seaward of the beach scarp on which waves expend most of their energy; site of the vigorous onshore and offshore movement of sand

Longshore Drift

movement of sediments parallel to shore, driven by wave energy

density, with differing colors and textures

Uneven deposition results in beach layering on the low-tide terrace, where sediments are separated by their:

4

The speed of a longshore current can approach _____ km/hr:

wave-driven ; current-driven

Longshore drift occurs through the _____ movement of sand and _____ movement of water and sand

an angle ; straight

Waves usually approach the shore at _____ and return _____ to the ocean due to gravity, resulting in a net movement of sediment down shore:

Longshore Current

a current running parallel to the shore in the surf zone, caused by the incomplete refraction of waves approaching the beach at an angle

southward

Net sand flow across the US East and West Coast is usually _____ , as storms originate from the north:

Rip Current

a strong, narrow surface current that flows seaward through the surf zone and is caused by the escape of excess water that has piled up in a longshore trough

longshore current

Rip currents form when incoming waves pile excess water on the surf zone fast than the _____ can carry it away:

Coastal Cell

the natural sector of a coastline in which sand input and output are balanced

submarine canyons

Coastal cells are bound by:

parallel

Sand is deposited _____ to the coast by longshore drift

perpendicular

Sand is eroded and introduced to a coastal cell:

rivers, onshore transport, and cliff erosion

Sand input into coastal cells is from:

wind, longshore transport, offshore transport in submarine canyons

Sand output of coastal cells if from:

tectonically passive, trailing edges of continents

Coastal cells become very large and smooth at:

Sand Spit

an accumulation of sand and gravel deposited down current from a headland; sand spits often curl at their tips

Bay Mouth Bar

an exposed sandbar attached to a headland adjacent to a bay and extending across the mouth of the bay

Inlet

a passage giving the ocean access to an enclosed lagoon, harbor, or bay

longshore current

Sand spits form where the _____ slows as it approaches a quiet beach: