Lake Tarawera is the largest of a series of lakes which surround the volcano Mount Tarawera in the North Island of New Zealand. Like the mountain, it lies within the Ōkataina Caldera. It is located to the east of Rotorua, and beneath the peaks of the Tarawera massif i.e. Wahanga, Ruawahia, Tarawera and Koa. Tarawera means "Burnt Spear", named by a visiting hunter who left his bird spears in a hut and on returning the following season found both the spears and hut had been burned down completely.
Geography
Lake Tarawera is above sea level, and has a surface area of . To the north-west is Lake Ōkataina, to the west as you go south, lakes Ōkāreka, Tikitapu and Rotokākahi and to the south-east Lake Rotomahana. Lake Tarawera township is on the western shore, between Lake Tarawera and Lake Ōkāreka. The main road access is from Rotorua to the west.
The lake was substantially affected by the eruption of Mount Tarawera on 10 June 1886 to the lake's east. There were changes in lake level and sediment carriage.
The lake has a large catchment. This includes Lake Tarawera's immediate catchment, being in area, and the catchment of the nearby higher lakes, being a total of , with an estimated mean annual precipitation of .
Water Flow
Lake Tarawera is filled primarily by water flowing through the volcanic rocks and ashes, only about 42% being from water flowing in streams, etc. The mean surface inflows are estimated to be:
Thus surface water inflows contribute which is less than the rainfall on the lake surface itself and much less than either the estimated total outflow from the lake approaching . Therefore there is a fair subsurface inflow into the lake.
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An estimate has been made of total inflows both surface and subsurface from the surrounding lake catchments
The main hot water sources are in the southern section of the lake at the Wairua Stream, Hot Water Beach and Te Puha and Tarawera fumaroles. There is also a small geothermal area at Humphrey's Bay, to the south of Lake Ōkataina. Water varies between and . Lake Tarawera's outflow at its north east end, has been heavily influenced by the local geology, with a mean discharged on the surface into the Tarawera River, which flows north-east into the Bay of Plenty. An estimate of subsurface outflow has been made by measuring flow below Tarawera Falls where total river flow has increased to .
Geology
Lake Tarawera has been modified by eruptions within the Ōkataina Caldera, most recently the 1314 ± 12 CE Kaharoa eruption and the 10 June 1886 eruption. Its current outlet control is where Tapahoro lava flows created by the 5526 ± 145 BP Whakatane eruption run into a 14,009 ± 155 BP Pokohu lava flow which the Tarawera River flows across in a wide channel. Before the Whakatane eruption it is thought the lake had a lower level than at present. Immediately after the Whakatane eruption its level increased by at least with gradual cutting down and Taupō Rift subsidence to a level just before the 1314 Kaharoa eruption of above present lake levels. The 1314 eruption blocked the outlet in a temporary dam to a temporary lake height of above present lake levels, which was subsequently eroded with a great flood at one stage, to reach by the time of European settlement first surveys below present lake level.
The lake outlet was blocked for two decades after the 1886 eruption and the lake level increased to a maximum of above its present level. The eruption killed over 120 people, and buried the Māori village of Te Wairoa on the southwest shore of the lake. The last major decrease in lake level occurred in a flood of 1904 down the Tarawera River valley after the new volcanic material dam first broke on 1 November 1904. The main flood surge on 3 November 1904 was assessed at a peak flow of . After 1906 it is now known that the main change in lake level relative to reference sea level would have been due to the slow subsidence of this area of the Taupō Rift. This rate can be estimated to have been about in 100 years from the nearest NZ Geonet station RGTA data which has been operative since November 2007 and shows a linear trend in height decrease since then.