Oruanui eruption

The Oruanui eruption of Taupo in Taupo Volcanic Zone on the North Island of New Zealand was a Vulkanexplosivitätsindex eight of the world's largest eruption of the last 70,000 years and one of the largest eruptions of the last 250,000 years.

It occurred about 26,500 years ago during the late Pleistocene and generated about 430 cubic kilometers of ash fall deposits, 320 cubic kilometers of pyroclastic flow deposits ( mainly ignimbrites ) and 420 cubic kilometers of primary ( directly going back to the conveyor products from this outbreak ) Intracaldera deposits, ie a total volume of 1170 cubic kilometers tephra, which corresponds to 530 cubic kilometers of bubble-free magma. A large part of today's Lake Taupo was directly related to the Oruanui eruption. The magma was conveyed alternately over several vents that are now in the underground of Lake Taupo.

The Oruanui eruption shows two unusual features: an episodic course as well as a wide range of deposits, both in terms of ash cases as well as the pyroclastic flow deposits.

Deposits

Stratigraphy

The deposits of the outbreak have been divided, of which the tenth and youngest While in the area worst preserved, but, as has been noted on the basis of locally well-preserved sections, the most powerful phase is divided into ten mappable units ( "phases" ). The activity breaks between the phases extend to a maximum of weeks to a few months, but usually only hours.

Ash cases

Distal deposits of the eruption, ie, those further away from the eruption center, consisting solely of Ash falls. They are found almost on the entire North Island and in the north east of the South Island of New Zealand. In the North Island, these deposits are obtained with thicknesses of more than two meters. On the Chatham Islands, which lie about 1,000 kilometers southwest of Lake Taupo, are still found 18 centimeters mighty deposits of ash dust, which are derived from the most recent phase of the outbreak.

Pyroclastic flow deposits

Proximal, ie with increasing proximity to the outbreak center, the ash pyroclastic flow deposits cases are stored and form the majority of the Oruanui sequence. They usually consist of layered and massive ignimbrites, cover a total area of ​​300 square kilometers, reaching locally widths of more than 200 meters and can be found in some cases even at distances of up to 80 kilometers from the shores of Lake Taupo.

The Oruanui caldera

The Oruanui caldera was created during the most recent phase of the outbreak. From today, more than 600 square kilometer Lake Taupo was previously assumed that he was more or less identical to the caldera. However, geophysical surveys painted a detailed picture of the Seeuntergrundes. In the actual caldera is only a 140 square kilometer area in the central area of ​​the lake. This area is a 228 -square-kilometer border zone, the so-called " Einbruchssaum " (English: collapse collar ) surrounded. The southern part of the lake is formed by a 155 -square-mile, grave asymmetric structure. While the reduction of these three areas of the lake is in direct connection with the Oruanui eruption, the 47 -square-mile extreme northeast of the lake is younger and was created during an eruption 1800 years ago.

Follow

The enormous quantities of volcanic material, which have been promoted during the outbreak and deposited in the surrounding area of the volcano, had great influence on the subsequent development landscape in the region. The periglacial climate that prevailed at the time of the Oruanui eruption in New Zealand ( corresponding to the Weichselian Glacial of Northern Europe ), impacted by the eruption an adverse impact on the development of a vegetation cover in the area of the Taupo volcano. The result was intense erosion of the pyroclastic deposits, so that large quantities of this material were discharged by rivers and deposited on the lower reaches again. This led inter alia to the fact that the Waikato River shifted its original course through the Hauraki Plains in the Hauraki Gulf to the west into the Hamilton Basin and empties into the Tasman Sea today.