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Shore platform at Whakataki Beach, near Castlepoint, Wairarapa

New Zealand straddles an active boundary between two of the many tectonic plates that make up the Earth’s crust: the Indo-Australian plate to the west, and the Pacific plate to the east. The North Island east coast runs parallel to the boundary between these two colliding plates, and a short distance offshore the ocean floor plunges to great depths where the Pacific plate is forced downwards under the overlying Indo-Australian plate. The building up and periodic releasing of tension between these two plates as they grind against each other is responsible for the many earthquakes that this region experiences.

Over the course of millions of years countless layers of sand and silt have accumulated on the ocean floor adjacent to this coast, eventually being compressed into solid rock as more and more sediments have accumulated above them. Tectonic forces have then forced these sedimentary rocks up above the sea surface, where they underlie much of the East Coast region as it is known today.

The layered nature of these rocks can be clearly seen along the coast. Wave action has eroded away these rocks to form spectacular shore platforms, often characterised by parallel ridges of hard sandstone where the softer mudstone layers in between have been worn away. In the case of the platform in this photograph, the previously horizontal rock layers have been folded and distorted during uplift so that they now reach the surface at a sharply dipping angle, offering a remarkable cross-sectional view.


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