Coastal processes

2008-04-16T03:31:00.000-07:00

Hello! We decided to make a blog for our geography project.
Our geography project is researching on the question" What gives differernt coasts and beaches their different colours"

How a beach is formed:
The sea has construtive waves and destructive waves. The sea can move great quantities of sand enough to form a beach. In many places the forming of a beach and its removal is a seasonal cycle.

How does the sea transport sediments?
Two separate processes result in the deposit of this sand and sediment on the shore.

Most sediment is suspended in sea water and transported along the coast by the longshore current, a stream of water flowing parallel to the beach that is created by the action of waves

breaking at an angle to shore.

Longshore transport can deliver up to a million cubic yards of sediment annually to a single beach.

In the second process, sand deposited onshore by the longshore current is then oscillated by waves breaking onto and receding from the beach. This continual onshore-offshore movement gradually pushes the sand along the beach edge.
Both the longshore transport of sediment along the coast and the movement of sand by waves along the foreshore are a part of the process called littoral drift.

The Different Coloured Beaches

White sand Beach

The primary component of typical beach sand is quartz, or silica (SiO2). Quartz is a hard mineral which, not having any cleavage planes, does not fracture easily. Quartz is found in many types of rocks. The quartz minerals are, clear to white. They can display any color.

Black sand

Black sand can be seen as a layer on top of silica sand in regions with high wave energy, on the flanks of volcanoes, and in areas where most of the source rock is mafic, or dark-colored and poor in silica.

This is how it happens…
1) Volcanoes such as Hawai'i's Mauna Loa produce lava flows that come into contact with the cold ocean water.
2) The extreme difference between the ocean temperature and the temperature of the flowing lava cause the lava to fracture into tiny shards of black glass.
3) This glass is collected by waves into beaches.
4) These are eroded by wave action and are broken into grains and clasts which are included in the black sand.

Green sand

Green sand is composed primarily of olivine crystals which erode out of basalt (lava) flows. The crystals are heavier than most sand types on the beach and remain behind when lighter sand grains are washed away by strong wave activity.

Olivines form at high temperatures and are green and glassy. They are common in basalts, especially those found of the ocean-floor, and in ultramafic rocks.

Red sand
On the far side of Ka'uiki Hill south of Hana Bay is Kaihalulu, AKA. Red Sand Beach.
The sand gets its red-black color from the crumbling cindercone hill that surrounds the bay.

In Conclusion

The different colours of the beaches are due to the different types of sediments it carry. The different colours are often due to volcanic action, however, it can also be due to te erosion from its nighbouring structural features. An example is the Red sand beach.

Pink sand Beach
Just an image without explanation….

Thanks for viewing our blog :D !

Geography Project'08-Coastal processes

Coastal processes