Denudation - Underground water and sea waves
Introduction
The river or water of snow melting partly evaporates and returns to the atmosphere, a part runs off on the surface in the form of trellis, gullies, and rivers to form a drainage system of the area, the remaining part sinks in the ground which forms the underground water.
The soaked water percolates downwards through pores between mineral grains and cracks in between them.
It is collected in the lower layers.
The quantity of underground water thus collected varies from place to place and season to season depending on topography, season, amount of rainfall, and rocks’ nature.
Porous and non-porous rocks
The amount of water percolation into the rock layer depends on the pore spaces or porosity as well as the permeability of rocks.
Permeability refers to the capacity of rocks to allow water through them.
A rock layer in which pore spaces are connected and allow the entry of water through them.
A rock layer in which pore spaces are connected and allow the entry of water it is called porous rocks.
A rock layer that does not allow the sinking of water is known as nonporous.
The porous rocks are permeable and the nonporous layer or hard rocks are impermeable.
Some layers like sand, gravel, and limestone are more permeable and water is allowed to flow freely. They are called
Aqua-water, for-bear, aquifer is a water-bearing rock and is a reservoir of underground water.
1. Hot springs
In the weak zones of the earth, underground water enters deep and comes into contact with hot rock beds and gets evaporated with the vapor pressure, the hot water comes out. These are known as hot springs.
2. Geysers
Hot water has erupted to a height of a few meters along with steam periodically. these are called geysers.
Sea waves
Waves, tides, and currents are important types of movement of seawater.
Among these, waves are the most important agents of denudation along the coastlines.
The sea waves slash the coast with great pressure and cause erosion.
The eroded materials are transported and deposited to form unique relief features along the coast.
Meaning of waves
The waves are formed with the sweeping of winds over the water surface. The pressure sets over undulating swells moving forward. These are called waves.
Characteristics
On the water surface, only the waves move but not water.
The highest elevation of the wave is called the crust
The lowest level of water between the waves is called the trough.
The elevation between the trough and crust is called wave height.
Like all other denudation agents, the sea waves also perform three major functions namely erosion, transportation, and deposition.
Erosional Features
1. Capes and bays
On exposed coasts, the continual action of waves on rocks of varying resistance causes the coastline to be eroded irregularly. E.g., granites and limestones, occur in alternate bands with softer rocks e.g., sand and clay. The softer rocks are worn back into inlets, coves or bays and the harder ones persist as headlands, promontories, or capes.
2. Cliffs and wave-cut-platforms
A rock rising vertically above seawater with a steep slope is called a cliff.
It is formed because the maximum impact of the sea waves is observed on the lower part of the coastal rocks and consequently the lower part of the rocks is eroded more rapidly than the upper part. In India, a number of sea cliffs are found along the Konkan Coast of India.
As the cliff retreats, a new landform is formed. This is a wave-cut platform. It is a gently sloping
Rock-cut flat surface. It is created at the bottom of the cliff face. It is not a smooth platform of
rock, rather it consists of ridges and grooves. The basic reason for the formation of a wave-cut platform is the recession of the cliff.
3. Sea caves
Waves continued to erode the base of a cliff along the weak rock beds. Initially, a hole is formed which is further expanded into a cave. these are most common in the coastal regions of limestone.
Transportation:
The waves while receding also transport the eroded materials. These are deposited in different locations in various forms to produce distinct relief features.
Depositional Features
The sea waves also transport the eroded materials and deposit these at other places.
Landforms resulting from deposition include platforms, beaches, bars & tombolo’s.
Beaches
Beaches are the most familiar of all the coastal landforms. They are the main feature of deposition found along the coast. They consist of all the material (sand etc.) built up between the high and low tide mark (High the tide is the highest level of the tide while low the tide is the lowest level of tide). There are a number of different sources of beach material. Rivers are the main source as fine mud and gravel are deposited at the mouth of a river. Other sources of beach material include constructive waves (bringing material up the beach from the sea) and cliff erosion. Beaches are temporary features. Beaches are called shingle beaches to contain excessively small pebbles and even cobbles. Marina Beach of Chennai and Kovalam Beach of
Thiruvananthapuram is a famous beach in India.
Sand Bars
Elongated sand deposits near the coast are called Bar.
These are formed at several locations such as
In between the capes.
In between the coastal and inland. These are called a tombolo.
Across the mouth of the river.
Spit
The waves deposit the eroded materials along the coast. At the one end, it is connected to the coast. On the other end, the material under the wave action is deposited in the oblique form. It is known as a hook or spit.
Coastlines of submergence
Coastlines of submergence are formed in Coastal areas which have become lowered below the current sea level. The cause is the rise in sea level is a consequence of ice melting since the last ice age. This group includes Ria, fiord, estuarine, and Dalmatian or Longitudinal coasts.
1. Ria Coasts
A ria coast is formed when a non-glaciated highland coast becomes submerged and the valleys filled with seawater. These submerged valleys are often V-shaped. This type of coast is found in north-western Spain and south-western Ireland.
2. Fiord (Fjord) Coasts
A fjord is a narrow, high-walled, and very long submerged glacial valley. Fjords are formed when a descending glacier carves a U-shaped valley into the bedrock. When these fjords are submerged fjord coast is formed.
3. Dalmatian or Longitudinal Coasts
These coasts are formed when a mountain ridge running parallel to the sea coast is submerged. In this mountain ranges become chains of islands resembling patches on the body of a Dalmatian dog.
4. Estuarine Coast
Estuary/estuarine coasts are coasts where lowland coasts are submerged, flooding rivers. Their entrances are sand and silt free, Thames of Britain are the example of such type of coasts
