Along this coast a hard rocky outcrop has become an island, cut off from the mainland by a flooded valley. Below the estuary, an...Read More >>Along this coast a hard rocky outcrop has become an island, cut off from the mainland by a flooded valley. Below the estuary, an arm of land is still linked to the mainland as a peninsula. A third outcrop has been wave-worn into an isolated pillar or stack, a sea arch and steep cliffs. Currents carry shingle from the bay’s beach, slow down and drop it to form a pointed spit and sand bar. Nearby, river mud is deposited to form a marshland and delta. Coastlines are where ocean or sea meets land. Some coastlines are shaped by the action of waves crashing against them, wearing away the rocks. Along others, sand and shingle are piled up in beaches or mudflats. The coast is a continuing battle between sea and land. Sometimes the sea “loses” as shingle, sand or mud piles up and the land grows. In other places, the sea “wins” as waves, currents and tides batter and break up the coast. Even hard rocks like granite are gradually worn away, especially during storms when high winds whip up huge waves powerful enough to smash pebbles and boulders against the shore.
The shape and features of a coastline depend on its rocks, winds and currents. Very hard rocks erode slowly and stand out as high headlands. Waves build up higher in the direction of the prevailing (or main) winds in the region. This means waves have their biggest effect on coasts exposed to these winds. Sometimes waves may carve a hole, or arch, right through a headland. If the roof of the arch later collapses, part of it is left standing alone in the sea. This is called a stack.
Horseshoe Bay, Queensland, Australia
The longest spit in the world is the 110-km (68-mile) Arabat Spit in the Sea of Azov, Ukraine.
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