Rangatauanui is a

maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow ...

lake south of

Ohakune Ohakune is a small town at the southern end of Tongariro National Park, close to the southwestern slopes of the active volcano Mount Ruapehu, in the North Island of New Zealand. A rural service town known as New Zealand's Carrot Capital, Ohaku ...

in the

North Island The North Island ( , 'the fish of Māui', historically New Ulster) is one of the two main islands of New Zealand, islands of New Zealand, separated from the larger but less populous South Island by Cook Strait. With an area of , it is the List ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

. It is in the area of the southernmost volcanic activity in the

Taupō Rift The Taupō Rift is the seismically active rift valley containing the Taupō Volcanic Zone, central North Island of New Zealand. Geology The Taupō Rift (Taupo Rift) is a intra-arc continental rift resulting from an oblique convergence in the H ...

. 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 The Ohakune volcanic complex (Ohakune craters, Rochfort Crater) is a small extinct monogenetic volcano south-west of Mount Ruapehu and just north of the town of Ohakune in Manawatū-Whanganui, New Zealand. It is in the area of the southernmost ...

and it is unclear if the maar lakes are similar potential Ruapehu parasites, representing the southernmost vents of the

Taupō Volcanic Zone The Taupō Volcanic Zone (TVZ) is a volcano, volcanic area in the North Island of New Zealand. It has been active for at least the past two million years and is still highly active. Mount Ruapehu marks its south-western end and the zone runs n ...

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 The South Kermadec Ridge Seamounts are a continuation of the volcanic island arc, formed at the convergent boundary where the Pacific Plate subducts under the Indo-Australian Plate. The subducting Pacific Plate created the Kermadec Trench, th ...

and

Kermadec Islands The Kermadec Islands ( ; ) are a subtropical island arc in the South Pacific Ocean northeast of New Zealand's North Island, and a similar distance southwest of Tonga. The islands are part of New Zealand. They are in total area and uninhabit ...

to beyond

Tonga Tonga, officially the Kingdom of Tonga, is an island country in Polynesia, part of Oceania. The country has 171 islands, of which 45 are inhabited. Its total surface area is about , scattered over in the southern Pacific Ocean. accordin ...

. Because the lake has no major inflows or outflows sediment cores have been undisturbed, and provide a useful dated

tephra Tephra is fragmental material produced by a Volcano, volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, ...

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 The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

. 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 New Zealand flax describes the common New Zealand perennial plants ''Phormium tenax'' and '' Phormium colensoi'', known by the Māori names ''harakeke'' and ''wharariki'' respectively. Although given the common name 'flax' they are quite disti ...

and also containing ''

raupō ''Typha orientalis'', commonly known as bulrush, cumbungi, or raupō, is a perennial herbaceous plant in the genus ''Typha''. It is native to Australia, New Zealand, Malaysia, Indonesia, Japan, Korea, Mongolia, Myanmar, Philippines, China and th ...

'', mānuka, and

cabbage trees Cabbage, comprising several cultivars of ''Brassica oleracea'', is a leafy green, red (purple), or white (pale green) biennial plant grown as an Annual plant, annual vegetable crop for its dense-leaved heads. It is descended from the wild cabba ...

. Within the surrounding reserve associated with the two lakes is regenerating native forest containing the trees

kahikatea ''Dacrycarpus dacrydioides'', commonly known as kahikatea (from Māori language, Māori) and white pine, is a Pinophyta, coniferous tree endemism, endemic to New Zealand. A Podocarpaceae, podocarp, it is New Zealand's tallest tree, gaining hei ...

kāmahi ''Pterophylla racemosa'', commonly known as the kāmahi, is an evergreen tree endemic to New Zealand. It is a member of the Cunoniaceae family of plants, and it is often referred to by its former botanical name ''Weinmannia racemosa.'' Most me ...

, and rewarewa, as well as the

epiphyte An epiphyte is a plant or plant-like organism that grows on the surface of another plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphyt ...

northern rātā Northern may refer to the following: Geography * North, a point in direction * Northern Europe, the northern part or region of Europe * Northern Highland, a region of Wisconsin, United States * Northern Province, Sri Lanka * Northern Range, a ra ...

Notes

References

Sources

* * * * * *{{cite thesis, last1=Moebis, first1=A., year=2010, title=Understanding the Holocene explosive eruption record of the Tongariro Volcanic Centre, New Zealand: a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand (Doctoral dissertation), publisher=Massey University, url=https://mro.massey.ac.nz/bitstream/handle/10179/2200/01_front.pdf Volcanic crater lakes Tongariro Volcanic Centre Volcanoes of Manawatū-Whanganui Lakes of Manawatū-Whanganui Protected areas of Manawatū-Whanganui