COASTAL LANDFORMS NOTES

COASTAL LANDFORMS

INTRODUCTION

Before we go into a discussion on the various landforms at the coast, it is important to learn the meaning of the various terms in this topic. This term include the following:-

(a)   Coast: The narrow strip of land from high tide inland

(b)   Coastline: Is the line forming a boundary between the land and sea water.

(c)    Shore: Is the land immediately bordering the sea or other large expanse of water.

(d)   Shoreline: Is the line where the shore meets the water.

(e)    Beach: Is the accumulation of loose materials such as sand and pebbles.

FACTORS INFLUENCING THE NATURE OF COAST

(a)   Nature of the rock

(b)   The work of waves

(c)    Change in the sea and land levels

(d)   Climatic condition

(e)    The work of man

(f)     The height of the land.

WAVES

These are the swells or forward movement of water in oceans caused by the friction of the wind on the water surface. The stronger the winds, the stronger the waves. The top of the wave is called the crest while the lowest part of a wave is called the trough. The distance between the crest is the wavelength while the wave height is the distance between the crest and the trough.

The broken waves advance toward the shore as swash and then retreat down the beach slope as backwash.

Types of waves

(a)       Constructive waves

(i)        They move materials towards the beach

(ii)      They break at a low frequency of less than ten waves per wave

(iii)     Their swash is stronger than the backwash

(iv)     They are flat and gentle

(v)       Have a low height

(vi)     Their wave length is longer

(b)      Destructive waves

(i)           They break at a high frequency of fifteen times per minute

(ii)          They have shorter wavelength

(iii)        They have a stronger backwash than swash

(iv)         They are steeper

(v)          They have a height of more than one metre

(vi)         They remove deposited material along the coast

WAVE EROSION

This is the marine processes which involves the wearing away or remove away the rock particles through the action of water in the ocean or seas.

Wave erosion operates on four processes. Namely

(a)       Abrasion

(b)      Hydraulic action

(c)       Solution

(d)      Attrition

FEATURES PRODUCED BY WAVE EROSION

CLIFFS: are steep rock faces along the coastline, they tend form along concordant coastlines with resistant rocks parallel to the coast. The erosion of a cliff is greatest at its base where large waves using actions such as hydraulic action, scouring and wave pounding actively undercut the foot of the cliff forming an indent called a notch, is cut by waves at high tide level and developed further, as this notch develops, a cliff is formed.

WAVE- CUT PLATFORMS : When the cliff steepens as the weathering attacks the base further, the cliff retreats, and the rock debris is swept by the backwash creating a -. - are shaped through the process of erosion

OFF-SHORE TERRACE

A wave- built terrace is the offshore zone composed of gravel and coarse sand. The base of the cliff forms the wave-cut platform as attrition (form of coastal or river erosion)causes the collapsed material to be broken down into smaller pieces, while some cliff material may be washed into the sea.

CAVES

Holes in the cliff face are enlarged by the wave erosion, and tunnel like openings are formed called caves. A cave is formed firstly by a cliff. The sea attacks the cliff and begins to erode the area of weakness such as the joints and cracks through the procedures of hydraulic action, wave pounding, abrasion and solution.

ARCHES

is created when a cave in a headland is eroded right through i.e. the inlet has two openings. An arch is formed when a cave is eroded, and where the fault lines run through the headlands, two caves will eventually erode into the back of each other forming an arch, passing right through a headland.

STACKS

When the arch collapses a pillar of rock remains behind as a sea stack. Stacks can be found close to cliff, where there is a high wave action. The way a stack is formed is when an arch collapses, leaving a stand of a boulder there

HEADLANDS

are formed in areas of alternating resistant and less resistant rocks. Erosion/wave action acts less on the more resistant rock creating headlands. Headlands are formed due to the presence of both soft and hard rocks. Because of this differential erosion occurs, with the soft, less resistant rock (e.g shale), eroding quicker than the hard resistant rocks (e.g chalk). Where the erosion of the sot rock is rapid, bays are formed. Where the is more resistant rocks, erosion is slower and the harder rocks are left to be sticking out into the sea as a headland.

BAYS

are indents in the coastline between two headlands. Bays are also formed in areas of alternating resistant and less resistant rocks. Erosion/wave action acts more on the less resistant rock creating bays. Where the erosion of the soft rocks is more rapid, bays are formed.