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Sinking Basins and Valleys

Uplifted mountains such as the Southern Alps and the North Island ranges stand out as spectacular features. But the push and pull of plate collision also causes large areas of the crust to sink or tilt down.

New Zealand Sedimentary Basins

Sedimentary basins: This tectonic downdrop provides large sediment traps that accumulate thick piles of eroded debris. Important resources can be found in these sedimentary basins, such as oil and gas reserves.

Ocean floor: On the ocean floor around New Zealand there are large troughs, subsiding back arc basins and also the deep sea trenches that mark the line of plate collision.

Faults: On a smaller scale, the Hutt Valley and Wellington Harbour are an example of local subsidence due to tilting of the land surface by local fault displacements.

Calderas: In the Taupo Volcanic Zone in the North Island, huge rhyolitic eruptions followed by collapse of the underground magma chambers have led to the creation of large caldera (collapsed craters) such as Lakes Taupo and Rotorua.

Drowned landscapes 2. Image: GNS Science.

Image: GNS Science.

Drowned landscapes: In some areas the sea has flooded old landscapes. The Marlborough Sounds are a large network of ancient river valleys that have been tilted to the north and drowned by subsidence of the crust on the western side of Cook Strait. Rising sea levels following the last ice age have added to the immersion of this landscape.

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