The Tama Lakes () are two

crater lake Crater Lake ( Klamath: ) is a volcanic crater lake in south-central Oregon in the Western United States. It is the main feature of Crater Lake National Park and is a tourist attraction for its deep blue color and water clarity. T ...

s in

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 ...

Tongariro National Park Tongariro National Park (; ), located in the central North Island, is the oldest national park in New Zealand and the sixth national park established in the world.Department of Conservation"Tongariro National Park: Features", retrieved 21 April ...

. They fill two (Upper and Lower Tama) of a series of explosion craters on the Tama Saddle between

Mount Ruapehu Mount Ruapehu (; English ) is an active stratovolcano at the southern end of the Taupō Volcanic Zone and North Island North Island Volcanic Plateau, volcanic plateau in New Zealand. It is northeast of Ohakune and southwest of the southern s ...

and Mount Ngaruahoe (a main

Mount Tongariro Mount Tongariro (; ) is a compound volcano in the Taupō Volcanic Zone of the North Island of New Zealand. It is located to the southwest of Lake Taupō, and is the northernmost of the three active volcanoes that dominate the landscape of ...

vent). Geologically the deep magma source and depth of basement are not usual for vents in the area.

Hydrology

The lakes are assumed to have subsurface drainage towards the springs that source the Waihohonu Stream that flows into the

Tongariro River The Tongariro River is a river in the North Island of New Zealand. The part of the Waikato River from the Waihohonu Stream, down to Lake Taupō, was formally named the Tongariro River in 1945. The river originates in the Central Plateau of the ...

as there are no outlet streams and even inlet streams are transient.

Geology

In the region of the southern Tama Lakes of the southern

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 ...

, the tens to hundreds of metre thick

Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...

greywacke Greywacke or graywacke ( ) is a variety of sandstone generally characterized by its hardness (6–7 on Mohs scale), dark color, and Sorting (sediment), poorly sorted angular grains of quartz, feldspar, and small rock fragments or sand-size Lith ...

basement is shallowest at approximately sea level, being somewhat higher under the volcanoes of Mount Ruapehu and Tongariro. Lava exists nearby that has been dated to 275,000 years ago, the oldest that contributed to the present Mount Tongariro massive. The Waihi fault is believed to have facilitated dyke intrusions in the area. The youngest

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, ...

from the Tama Lakes vents is dated to about 11,000 years ago. This is the Wharepu tephra layer in the Mangamate tepra formation and started as

phreatomagmatic eruption Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions cont ...

s but ended in a

pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...

up to to the south-east of the lakes. This youngest eruption happened after 11,200 years and before 10,900 years before 1950, and produced a tephra volume of at least . This eruption came by fast ascent from a deep magma reservoir at between depth unlike the much shallower depth of recent Mount Ngaruahoe eruptions. The Tama lakes vents had often previously erupted at very similar times to other Tongariro vents during this very active period for them about 11,000 years ago. The Oturere member of the Mangamate formation was erupted over less than a month with the largest eruption being at the Tongagiro Half Cone vent, but at least three other tephra falls came from Tama Lakes area. At least one of the earlier Tama Lakes eruption columns collapsed generating another pyroclastic flow to the south-east of the lakes that was in volume. The last eruption from a Tama Lakes area vent in this sequence was after the Half Cone vent was no loner active. Later after further activity at Half cone alone (Waihohonu member of the Mangamate formation) there was again paired activity with this vent by Tama lake area vent(s) over at least 2 months with evidence of explosive magma–groundwater interaction.

References

Sources

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External links

Aerial photo of the Tama Lakes
{{Tongariro National Park Tongariro Volcanic Centre Volcanoes of Manawatū-Whanganui Volcanic crater lakes Tongariro National Park

Hydrology

Geology

References

Sources

See also

External links