Coastal Landforms

COASTAL EROSIONAL LANDFORMS

Erosional landforms dominate rocky coasts

Most coastal erosion is accomplishedthrough the unceasing pounding of theshoreline by waves.

Waves have tremendous power after theybreak, with the associated spray moving asfast as 113 km/h (70 mi/h).

Headland: A headland is a promontory that jutsinto the ocean or sea and thus is surrounded onthree sides by water.

Wave refraction: The process through whichwaves are focused and bent around headlands.

Retrogradation: The process through which ashoreline retreats through erosion.

Rocky coasts fall into three chief types:

Landforms of cliffs and platforms

Several coastal features of rocky coasts are associated with the shore platforms and plunging cliffs ; cliffs, notches, ramps and ramparts, and Several small-scale weathering (including solution pools and tafoni, ) and erosional features.

Indeed, shore platforms, caves, stacks, arches, and many other landforms routinely form conjointly.

Cliffs are steep or vertical slopes that rise precipitously fromthe sea or from a basal platform.

Notches are Cliff-base signs of cliff erosion

Nips: Shallow notches are sometimes called nips.

Ramps occur at cliff bases and slope more steeply than therest of the shore platform. They occur on sloping andhorizontal shore platforms.

Ramparts: Horizontal shore platforms may carry ridges,perhaps a metre or so high, at their seaward margins.

Marine potholes are roughly cylindrical or bowlshapeddepressions in shore platforms that are ground out by theswirling action of sand, gravel, pebbles, and bouldersassociated with wave action.

Caves, arches, stacks, and related landforms

Sea cave is a hollow excavated by wavesin a zone of weakness on a cliff.

Arch: Where waves attack a promontoryfrom both sides, a hollow may form at thepromontory base form a sea arch.

Sea Stack: The toppling of a sea archproduces a sea stack.

Gorge is a narrow, steep-sided, and oftenspectacular cleft, usually developed byerosion along vertical fault planes orjoints in rock with a low dip.

COASTAL DEPOSITIONAL LANDFORMS

Beache: Beaches are the most significantaccumulations of sediments along coasts. They form inthe zone where wave processes affect coastalsediments.

Pebble beachescommon at middle and high latitudes, pebbles aresupplied by coarse glacial and periglacial debris.

Sand beachesare prevalent along tropical coasts, rivers carry

sediments and cliff erosion donates little tolittoral deposits .

Under some conditions, and notably in the tropics,beach sediments may, through the precipitation ofcalcium carbonate, form beachrock.

Beach profile

Spits, barriers, and related forms

Spit: Beaches attached to the land at one end are spits, Spits are longer than they are wide,

Foreland: Beaches attached to the land at one end are forelands, forelands are wider than they are long.

Beaches that are attached to the land at two ends arelooped barriers and cuspate barriers,tombolos, andbarrier beaches.

Beaches detached from the land are barrierislands.

Beach ridges and cheniers

Beach ridges formed where sand or shinglehave been stacked up by wave action alonga prograding coast.

Cheniers are low and long ridges of sand,shelly sand, and gravel surrounded bylow-lying mudflats or marshes

Coastal sand dunes

Coastal dunes are heaps of windblown sedimentdeposited at the edge of large lakes and seas

made from sediment blown off a beach to accumulate in areas sheltered from the action of waves and currents.

Small, crescentic dune fields form at the back of bays enclosed by rocky headlands

larger prograding dune fields form on straight,sandy coasts that are exposed to prevailing and dominant onshore winds.

Estuaries

Estuaries are tidal inlets, along a river to the highest point reached by the tide.

partially enclosed but connected to the open sea.

transition zones between rivers and the sea in which fresh river water mixes with salty ocean water.

shape is determined by coastal topography, but this changes fairly rapidly as sedimenterosion and deposition reach a steady state.

Tidal flats, salt marshes, and mangals

Currents associated with tides carry copious amounts ofsediment inside areas of shallow water. The ebb and flowof tidal currents fashions a range of coastal landforms.

Tidal flats

Tidal flats are banks of mud or sand that are exposed at low tide.

high-tide flat (a gently sloping surface that is partly submerged at high tide);

Intertidal slope (a steeper but still gently inclined zone lying between the high-tide flat and the lower tidal limit);

subtidal slope, which is submerged even at low tide

Salt marshesSalt Marshes form when tidal flats are highenough to permit colonization by salt-tolerantterrestrial plants.

MangalsMangals are communities of mangroves –shrubs and long-lived trees and withassociated lianas, palms, and ferns – thatcolonize tidal flats in the tropics, and occur inriver-dominated, tidedominated, and wave-dominated coastal environments

Marine deltas

Marine deltas are formed by deposition whererivers run into the sea. Some deltas aretriangular in plan, like the Greek letter delta, ,after which they were named almost 2,500years ago by Herodotus.

Some deltas form along low-energy coasts withlow tidal ranges and weak waves.

Others form in high-energy coasts with large tidalranges and powerful waves.

TYPES OF DELTA

Based on their overall morphology, six basic delta types are recognized that may be classified according to the importance of ;river, wave, and tidal processes.

Type 1 deltasdominated by river processesareas with a low tidal range,very low wave energyfine-grained suspended load

Type 2 deltasdominated by tidesoccur in areas with a high tidal range and strong tidal currentslow wave energy,Ganges–Brahmaputra in Bangladesh

Type 3 deltasaffected by waves and tidal currents.areas of intermediate wave energy,moderate to high tidesMekong Delta in Vietnam

Type 4 deltasintermediate wave energylow tidal range.low sediment yieldsHorton Delta in Canada.

Type 5 deltasriver-borne sandsmoderate to high wave energyoffshore slopes are moderate to steepwave redistributing of river-borne sandsSão Francisco in Brazil

Type 6 deltastotally dominated by wave actionsteep offshore slopes.Shoalhaven in New SouthWales,

Coral reefs and atolls

A coral reef is a ridge or mound built of the skeletal remains of generations of coral animals, upon which grow living coral polyps. Reefs typically grow in shallow, clear waters of tropical oceans.

An atoll is a ring of coral reef and small sandyislands that encircles a shallowlagoon.Atollsarecommon in the tropical PacificOcean, wheresuch groups of islands as the Marshall Islandsand Kiribati are chains of atolls.

The End