Why are there so many volcanoes in New Zealand?

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30/01/2002                                                                  Prasshy.S

Why are there so many volcanoes in New Zealand?

        ‘Geography is the study of places; the physical processes that shape them and the people that live them. This essay is about volcanoes in parts of New Zealand (see map). The volcano I’m writing about is Ruapehu. I will be writing about the volcano’s seismic activity and tectonic activity.  Ruapehu is in the North Island in New Zealand. It is situated in 39.28 South and 175.57 East. New Zealand is the middle where the tectonic plates are. When a volcano erupts, molten rock is thrown out. This then turns into lava. There is a cross section of Ruapehu (see labeled diagram).  The people living near the volcano in good ways and bad ways. When the volcano erupts it leaves a layer of very good soil, which is good to farm in. Places with volcanoes are also very good tourists attractions. We watched two videos named ‘Tectonic Activity in New Zealand’ and ‘Volcanoes-disasters’.

                

        Volcanoes are openings in the ground where magma from deep inside the earth forces its way to the surface. The magma may appear as flows of molten lava, as volcanic bombs, as fragments of rock or simply as ash and dust. Mountains that are made of these materials are called volcanoes (see labeled diagram).   

Ruapehu volcano is the southernmost of the large active volcanoes of the North Island. Rising to 2797m (9175 ft), Mount Ruapehu is the highest mountain in the North Island and the most recent of the North Island volcanoes to have erupted. Ruapehu is located at the southern end of the Taupo Volcanic Zone (TVZ). Sinking in the central axis of the TVZ had led to well known active faults developing to the east and west of Ruapehu volcano, which are downthrown towards the mountain. These faults mark the boundary of the TVZ in this region, which stops 20 km south of Ruapehu’s summit. Ruapehu is largely comprised of the volcanic rock andesite. Accumulations of andesite lava flows inter bedded with fragmental rubble radiating from the summit region forming a stratovolcano that rises 2000 meter from the surrounding lowlands. As stratovolcanoes build up, they become steep and are capable of collapsing and generating debris, avalanches and lahars that spread outwards onto the surrounding lowlands. These lowlands form a roughly circular apron of fragmented rocks. Mantling the lowlands is various thickness of volcanic ash forming the parent material of most of the soil in the region. Dominating the summit area is a crater lake which, when full to overflowing contains 8-10 million m3 of acid waters. During historical eruptions (in 1945 and 1995) the lake water has been ejected out of the crater and onto surrounding glaciers, and/or propelled across the outlet and into the Whangaehu catchments. Throughout history, lahars have been responsible for much loss of life in the countries of the Pacific margin, including New Zealand.

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The beginnings of volcanic activity at Ruapehu are shrouded in the mists of time but early evidence comes from andesite pebbles preserved on an uplifted marine bench in the Wanganui district. These pebbles, which are about 300,000 years old, are the remnants of an andesite lava flow, which was emplaced following eruptions from an early volcano in the vicinity of Ruapehu. The pebbles were then transported by a proto-Whanganui River to their present position. The oldest lava sequences preserved in site are exposed on the northern flank of Ruapehu and seem to date from this time. This material comprises massive and ...

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