Rangatauanui


Rangatauanui is a maar lake south of Ohakune in the North Island of New Zealand. It is in the area of the southernmost volcanic activity in the Taupō Rift. Its undisturbed lake sediments have proved useful in reconstructing recent climate proxy records for New Zealand.

Geography

It is south of Ohakune in the Ngā Roto-o-Rangataua Scenic Reserve, which before 2019 was known as the Ohakune Lakes Scenic Reserve. This has an area of about the about. Historically it has been called Rangataua Crater Lake. Adjacent is another smaller maar lake, Rangatauaiti, in the area that has been called the Rangataua craters in the geological literature.

Geology

Along with Rangatauaiti it is a maar lake, believed to have been formed about 30,000 years ago. The nearest other volcanoes are to the north, being the Ohakune volcanic complex and it is unclear if the maar lakes are similar potential Ruapehu parasites, representing the southernmost vents of the Taupō Volcanic Zone which is defined as terminating at Mount Ruapehu. The structure of the southern Ruapehu magma system is unknown and evidence exists in the case of the Ohakune volcanic complex for an approximately depth for the originating magma reservoir, fair magma ascent rates and that the magma conduit may be independent of the main feeder system of Mount Ruapehu. Either way these volcanoes may be the present propagating tip of the arc system that extends from the Taupō Rift through the South Kermadec Ridge Seamounts and Kermadec Islands to beyond Tonga.
Because the lake has no major inflows or outflows sediment cores have been undisturbed, and provide a useful dated tephra record of nearby eruptions.

Climate studies

Consistent with Tasmanian and Chilean studies there is a peak in summer temperatures at about 16,000 years ago similar to the later Holocene. Summer temperatures then cooled from 14.5 to 12.9 BP, before peaking at 11.7 cal ka BP. Forest developed after 11.5 BP, similar to today's and the climate record here is consistent with other New Zealand Holocene studies.

Ecology

Currently the lake is surrounded by wetland for dominated by New Zealand flax and also containing raupō, mānuka, and cabbage trees. Within the surrounding reserve associated with the two lakes is regenerating native forest containing the trees kahikatea, kāmahi, and rewarewa, as well as the epiphyte northern rātā.