AIR PRESSURE

DEFINITION
AIR PRESSURE IS THE DOWNWARD FORCE EXERTED BY THE WEIGHT OF AIR PER UNIT AREA ON THE EARTH’S SURFACE.
AIR PRESSURE MAY VARY WITH ALTITUDE AND TEMPERATURE.
AIR PRESSURE IS GREATER AT THE SEA LEVEL AND DECREASES WITH INCREASING ALTITUDE.

INSTRUMENT USED
BAROMETER

BAROMETER

MERCURY BAROMETER

ANEROID BAROGRAPH

ANEROID BAROMETER

ISOBARS IS THE LINES ARE JOINING PLACES WITH EQUAL PRESSURE.
UNIT MEASUREMENT IS IN MILLIBARS
TYPES OF PRESSURE
RISING WARM AIR IS LESS DENSE AND EXERTS LOW PRESSURE.

SINKING COLD AIR IS MORE DENSE AND EXERTS HIGH PRESSURE.

AS THE RESULT OF THE DIFFERENCE IN AIR PRESSURE BETWEEN TWO PLACES WIND IS FORMED.

HIGH PRESSURE + LOW PRESSURE = WINDS

FORMATION OF SPITS AND TOMBOLOS

A Spit is a long, narrow ridge of deposited materials that extends from the mainland into the sea. An example in Brunei is Muara Spit and Kuala Tutong Spit.
When the spit is connected the island to the mainland to form a feature is called the Tombolos.

Spits & Tombolos

The long shore drift transports materials along the coast. If there is a sudden change in the direction of the coast, the longshore drift continues to transport the materials in the original direction to the deep sea
As the longshore drift enters the deep water, the materials are deposited. Over time, these materials accumulate above the water to form a spit.
The spit continues to grow with the continuous deposition of materials.
The spit join a nearby island to the mainland to form a tombolo.

formation of Spits

FORMATION OF OFFSHORE BAR

Off shore bar is a long narrow ridge of deposited materials sand can be found lying away from and parallel to a coast.

OFFSHORE BAR

When the waves approach a gently sloping coast , friction between the waves and the sea bed causes the waves to break at some distance from the coast.
Over time, more materials  are built up parallel to the coast to form ridge of sand called offshore bar.
A body of coastal water may be partially or completely cut off from the open sea by the offshore bar. The body of water is called a lagoon.

COASTAL DEPOSITION

Deposition occur along the coast due to the
Constructive waves which have a more powerful swash than backwash, more materials are deposited than eroded on such coasts.
when the coasts are sheltered from prevailing winds which protected from wave erosion and deposition of materials take place.

Storm also subsidies, the large amount of materials eroded from the coast  than transport away from the coast. Hence, these materials are deposited.

Depositional features

1. Beaches
2. Offshore bars
3. Spits and tombolos
4. Coastal dunes

COASTAL TRANSPORT

The materials that are eroded from the coast are usually transported along the coast by waves and currents before they are deposited elsewhere.

The Longshore  Drift

When waves approach a coast at an  angle, the swash brings the sediment up onto the coast at the same angle.
Due to friction and the pull of gravity, the sediment is then brought seawards by the backwash at a right angle to the coast.

LONGSHORE DRIFT MOVEMENT

The sediment is picked up again by the next wave and carried up and then down the coast again.
This repeated zig zag movement of the sediment shifts the sediment along the beach.
A long shore drift is the movement of sediment along the coast when waves approach the coast at an angle

LONGSHORE DRIFT VIDEO