Leaving Certificate Physical Geography
Q:
2012 Q 2 (B)
Explain with the aid of a labelled diagram(s) the formation of one
landform of deposition that you have studied. (30 marks)
A sand bar is a sand spit that has extended out across a bay. It is formed by the
processes of deposition, long shore drift, constructive waves and wave refraction. A
sand spit develops where a coastline changes suddenly and the long-shore drift
cannot keep moving in a zigzag movement of sediment along the sea shore.
Sand, shingle, gravel and stones are deposited in the slow water in the
changing coastline by the process of deposition. Over time it builds up until it
reaches the sea surface and becomes a base for the finer material to be deposited on
top by the process of long shore drift in the bay mouth.
As the spit continues to grow, the constructive waves deposit their load as
they pass over the deposits. Fine sand is added to the spit by the large powerful
winds that blow in from the beaches. This creates sand dunes on the land side of the
spit. Marram grass begins to grow to keep the sand dunes stable with their deep,
deep roots.
The spit develops a curved end at the end. This is due to the process of wave
refraction where the strong waves bend around the edge of the spit, creating a
curved shape.
Over time, the spit extends to the whole length of the mouth of the bay. There
must be no river estuary or rivers flowing into the bay as they wash away all the
deposits, preventing spit bars
As the sand bas has blocked the mouth of a bay, the trapped sea water
becomes a lagoon of seawater. During storms huge waves may wash over the
sandbar, throwing deposits into the lagoon with them.
The lagoon eventually becomes a salty marsh as the water evaporates.
Vegetation such as reeds, bullrushes and coarse vegetation may grow in the
sediment.
The two types of sand bars are known as Baymouth sand bars and Offshore
sand bars. Baymouth sand bars form across bays whereas an offshore sand bar
forms out at sea. These sand bars may be pushed by the waves to the mouth of a bar
to form a Baymouth sand bar.
In conclusion, this is the formation of a sand bar. A sand spit forms due to the
processes of deposition, constructive waves, wave refraction and long-shore drift.
Labelled diagram: