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52-495: Lake Rotomakariri (From Māori : roto , meaning lake, and makariri , meaning cold) was a lake which formerly existed in the basin that is now occupied by Lake Rotomahana , in the Bay of Plenty region of New Zealand's North Island . The lake's name was in contrast to the nearby Lake Rotomahana, which prior to the 1886 eruption of Mount Tarawera , was a shallower warm water lake. Prior to this eruption, Lake Rotomakariri sat in

104-415: A composition very close to the water-saturated granite eutectic and with extreme enrichment in most incompatible elements . However, they are highly depleted in strontium , barium , and europium . They are interpreted as products of repeated melting and freezing of granite in the subsurface. HSRs typically erupt in large caldera eruptions. Rhyolite is common along convergent plate boundaries , where

156-561: A natural glass or vitrophyre, also called obsidian . Slower cooling forms microscopic crystals in the lava and results in textures such as flow foliations , spherulitic , nodular , and lithophysal structures. Some rhyolite is highly vesicular pumice . Peralkaline rhyolites (rhyolites unusually rich in alkali metals) include comendite and pantellerite . Peralkalinity has significant effects on lava flow morphology and mineralogy , such that peralkaline rhyolites can be 10–30 times more fluid than typical calc-alkaline rhyolites. As

208-406: A new lake formed in the most western part of the new Rotomahana crater, and this larger lake was called during its roughly decade of existence, the new Lake Rotomakariri. The area of the lake and the old Lake Rotomahana were volcanic as part of the Ōkataina Caldera and occupied an area that later became a vent of the 1886 eruption. There were some sinter cones near the lake. As the deepest part of

260-507: A rather desolate landscape of the fresh eruptives exist. In due course Lake Rotomahana expanded again to ten times its previous area to occupy much of a crater produced by the 1886 eruption. This expansion has drowned the positions occupied by both the old and new Lake Rotomakariri, as the present Lake Rotomahana is 35–37 m (115–121 ft) above the old Lake Rotomahana according to one source, and 48 m (157 ft) according to another. The old Lake Rotomakariri had swampy surrounds and

312-595: A result of their increased fluidity, they are able to form small-scale flow folds, lava tubes and thin dikes. Peralkaline rhyolites erupt at relatively high temperatures of more than 1,200 °C (2,190 °F). They comprise bimodal shield volcanoes at hotspots and rifts (e.g. Rainbow Range , Ilgachuz Range and Level Mountain in British Columbia , Canada). Eruptions of rhyolite lava are relatively rare compared to eruptions of less felsic lavas. Only four eruptions of rhyolite have been recorded since

364-633: A result, many eruptions of rhyolite are highly explosive, and rhyolite occurs more frequently as pyroclastic rock than as lava flows . Rhyolitic ash flow tuffs are the only volcanic product with volumes rivaling those of flood basalts . Rhyolites also occur as breccias or in lava domes , volcanic plugs , and dikes . Rhyolitic lavas erupt at a relatively low temperature of 800 to 1,000 °C (1,470 to 1,830 °F), significantly cooler than basaltic lavas, which typically erupt at temperatures of 1,100 to 1,200 °C (2,010 to 2,190 °F). Rhyolites that cool too quickly to grow crystals form

416-404: A shallow basin surrounded by marshes, draining into Lake Tarawera by Awapurohe Creek and Rotomahana's outflow of Kaiwaka Stream. The eruption of Mount Tarawera initially destroyed Lake Rotomakariri and its lakeside village with the loss of 19 lives, though water entering the new crater gradually refilled Lake Rotomakariri after volcanic activity subsided. As water accumulated over the decade after

468-672: A slab of oceanic lithosphere is being subducted into the Earth's mantle beneath overriding oceanic or continental lithosphere . It can sometimes be the predominant igneous rock type in these settings. Rhyolite is more common when the overriding lithosphere is continental rather than oceanic. The thicker continental crust gives the rising magma more opportunity to differentiate and assimilate crustal rock. Rhyolite has been found on islands far from land, but such oceanic occurrences are rare. The tholeiitic magmas erupted at volcanic ocean islands, such as Iceland , can sometimes differentiate all

520-449: A sunken forest or trees, as reported by Fitzgerald off Moura. While there were forests over the pre-eruption Mt Tarawera, Tōtara trees were scattered and only recorded over the western and southern mountain flanks.   Given Tōtara tree groves could hardly appear in the eruption craters; it appears likely any sunken forest lies in the north-east corner of the new lake. The placement of the sunken forest would have been post-eruption, via

572-409: Is incorrect. He followed August Petermann's flawed map. Hochstetter shows the lake axis lay at an azimuth of 355 degrees. Recent research into these lake levels gave insight into changes at Lake Rotomahana in the lead-up to the eruption. One forgotten lake feature is the semi-mythical sunken totara forest of Lake Rotomahana. In 2016 when a scuba team first dove the lake, they found no evidence of

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624-491: Is one of the most studied lakes in New Zealand, occupying the southwestern portion of a 17-kilometre-long (11 mi) rift which formed during the 1886 eruption of Mount Tarawera . In the context of the geological discussion it is important to note a high standard hydrophonic survey took place in 2016 and the actual absolute measurements taken at this time, as lake level varies, are used for geological baseline. At this time

676-407: Is rhyolitic volcanic glass , has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge. Rhyolitic pumice finds use as an abrasive , in concrete , and as a soil amendment . Rhyolite is an extrusive igneous rock, formed from magma rich in silica that is extruded from a volcanic vent to cool quickly on the surface rather than slowly in

728-427: Is such that the present Lake Rotomahana has now no surface drainage to Lake Tarawera and is separated from it by a ridge rather than the former stream bed which all agree is buried by them. The mud from at least one of the two main old lakes was distributed to the northwest and for a period provided richer, healthier farmland as the basalt component contains more cobalt than cobalt poor rhyolite and this deficiency issue

780-454: The Ōkataina Caldera . It is the most recently formed larger natural lake in New Zealand, and the deepest in the Rotorua district. The New Zealand Ministry for Culture and Heritage gives a translation of "warm lake" for Rotomahana , following Hochstetter . and the surrounds of the lake had become world famous following its first European written description in 1843. Lake Rotomahana

832-552: The Kaiwaka Stream. This stream drained mainly Lake Rotomahana and was quite swift, so canoes had to be poled up it from Lake Tarawera . It had a fall of 12 m (39 ft) in 1.6 km (0.99 mi). On the north-eastern lake shore was the village of Waingōngongo. The old Lake Rotomakariri was only 0.54 km (0.34 mi) long. There were several other small ponds or lakes to the east of Lake Rotomakariri towards Mount Tarawera, with Hochstetter showing an unnamed one to

884-498: The Pink and White Terraces lie preserved at a depth of 10–15 metres (32–49 ft). The researchers were hoping to raise funds for a full survey of the area, but any work would first have to be approved by the local Māori tribe on whose sacred ancestral land the Pink and White Terraces are situated. Ground penetrating radar searches were undertaken in 2017 but the equipment failed to penetrate sufficiently deeply to show whether or not

936-620: The R field of the TAS diagram . The alkali feldspar in rhyolites is sanidine or, less commonly, orthoclase . It is rarely anorthoclase . These feldspar minerals sometimes are present as phenocrysts. The plagioclase is usually sodium -rich ( oligoclase or andesine ). Cristobalite and trydimite are sometimes present along with the quartz. Biotite , augite , fayalite , and hornblende are common accessory minerals. Due to their high content of silica and low iron and magnesium contents, rhyolitic magmas form highly viscous lavas . As

988-470: The Rotomahana crater bottom is 185 m (607 ft) above sea level. The lake's northern shore lies close to the 39-metre (128 ft) lower Lake Tarawera , separated by less than 700 metres (2,300 ft) of terrain that is mostly material from the 1886 eruption. The original Lake Rotomahana has a slightly controversial level with respect to that of Lake Tarawera before 1886, partially because

1040-534: The Tarawera eruption and Lake Rotomahana is explained.   Rhyolite Its high silica content makes rhyolitic magma extremely viscous . This favors explosive eruptions over effusive eruptions , so this type of magma is more often erupted as pyroclastic rock than as lava flows . Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock formations. Rhyolitic tuff has been used extensively for construction. Obsidian , which

1092-541: The catchments in the Ōkataina Caldera predict that the Lake Rotomahana catchment is contributing subsurface to the Lake Tarawera catchment with an outflow, depending upon the size of the catchments so defined, of between 1,125–3,018 L/s (39.7–106.6 cu ft/s). Before the 1886 eruption, two small lakes were present in the current lake's basin and perhaps six smaller ponds. The other lake

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1144-401: The east and to the south east a Lake Rangarua Tapu. European accounts gave a lake to the east, the name Green Lake, which, as many have had the same name in the locality over time, is almost meaningless. The present Green Lake to the east, occupying an explosion crater near the south-east shore of Lake Rotomahana did not exist prior to 1886. After the eruption which totally destroyed the old lake,

1196-486: The eighth wonder of the natural world and were New Zealand's most famous tourist attraction during the 19th century, from c. 1870-1886; but were buried or destroyed by the eruption. Scientists thought they had rediscovered the lower tiers of the Pink and White Terraces on the lake bed at a depth of 60 metres (200 ft) in 2011. More recent research reports over 2016-2020 suggest the upper parts of both terraces lie on land and may therefore be accessed for physical evidence

1248-430: The eruption also changed the level of Lake Tarawera and there was a later lowering of Lake Tarawera's level around 1904. The consensus range of difference with current water level between the old and current Lake Rotomahana appears to be 35–48 m (115–157 ft). The original lake formed in an area of mostly rhyolytic eruptives and would have also been associated with lake sediments deposited at least in

1300-421: The eruption, Lake Rotomakariri was absorbed by the larger Lake Rotomahana, which eventually rose to about 36–48 m (118–157 ft) above its pre-eruption level due to the previous outflow of the basin being blocked by ashfall. The Māori name Rotomakariri means cold water lake, and was first used by Hochstetter . This is in contrast to the larger warm lake Rotomahana just to its west on whose shores were

1352-469: The eruption, a number of craters filled over the course of 15 years to form today's Lake Rotomahana. As a result it is the most recently formed large natural lake in New Zealand, and at 118 m (387 ft) deep, the deepest in the Rotorua district. The former official depth was previously 112.4 m (369 ft), at a lower lake level and with less precise equipment. The lake bottom currently has up to 37 m (121 ft) of sediments, which means

1404-508: The extrusive equivalent of granite. However, while the IUGS recommends classifying volcanic rocks on the basis of their mineral composition whenever possible, volcanic rocks are often glassy or so fine-grained that mineral identification is impractical. The rock must then be classified chemically based on its content of silica and alkali metal oxides ( K 2 O plus Na 2 O ). Rhyolite is high in silica and total alkali metal oxides, placing it in

1456-507: The famous Pink and White Terraces that like all these features were destroyed or buried in the 1886 eruption. The only high quality survey of the lake area before this eruption had been done by Hochstetter in 1859, despite this area rapidly becoming a famous exotic geological tourist destination. High quality pictures of the then Lake Rotomahana and associated tourist attractions were widely available in Europe by 1875. The first Lake Rotomakariri

1508-543: The geological processes assumed to have occurred that erupted lake type mud deposits. The volcanics before the eruption were likely of rhyolite origin but after the eruption would have had new basaltic components. One or other of these lakes is the likely origin of shells of water-snails found, in a sample of fresh ash from Tauranga , and in an ash sample from Cape Runaway . The eruption accordingly likely both destroyed features, but could have covered them in eruptives which are meters thick. The depth of some of these eruptives

1560-408: The lake level was 340 m (1,120 ft), not the geographically mapped height of 337 m (1,106 ft), or the mean height of 338.7 m (1,111 ft). Lake Rotomahana has no natural surface outlet, and its water level varies by about one metre in response to rainfall and evaporation. There is now an engineered surface channel to maintain maximum lake level. Hydrogeologic models of

1612-472: The lake shore and had fed the Pink Terraces at the western side of the lake, has a heat flux of 21.3 W/m . There is an area southwest of Pātītī Island that has a heat flux averaging 13 W/m that appears to be in a lake floor crater created in 1886. The lake is a wildlife refuge (and was one prior to first contact), with all hunting of birds prohibited. A healthy population of black swan inhabits

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1664-472: The lake, and there are efforts underway to ensure the lake's largest island, Pātītī Island, is kept pest-free. Recent research confirms Pātītī Island is the closest surviving pre-eruption feature on the old lake, i.e. to survive the 1886 eruption, being formerly known as Rangipakaru Hill. There is no public access to the lake, save for the Tourist Track, overland from Lake Tarawera. A boat cruise on

1716-610: The lake, visiting hydrothermal features on the lake's shore, is available as an additional extra from the Waimangu Volcanic Valley tourism operation. The nitrogen load on the lake is stable, but has high trophic level index inflow from the Okaro catchment via the Haumi Stream. The Pink and White Terraces were a natural wonder on the shores of the lake before the 1886 eruption. They were considered to be

1768-532: The mechanism described by the US Forest Service after the Mt. St. Helens eruption. The trees were uprooted in the eruption and propelled into the crater during or after the eruption. As the new lake formed over decades, the trunks floated for a time, then tipped vertically; later descending into a vertical lie, and became embedded into the lake floor coming to resemble a sunken forest. Hence, another myth about

1820-460: The much larger Lake Rotokakahi (Green Lake) , which lies to the west of Rotomahana. Green Lake was formed in a roughly circular crater and is some 100 metres in diameter. It takes its name from its distinctive colour, which is considerably greener and darker than that of Rotomahana. The lake formed after the 1886 eruption of Mount Tarawera. Prior to the eruption, a small (~12m diameter) lakelet also known as Green Lake (Lake Rotopounamu) had existed to

1872-418: The new crater evacuated material to a depth of at least 60 m (200 ft) where the pre-eruption lakes had been and possibly as much as 80 m (260 ft) in places. The current average conductive heat flux is at least three times higher than that either beneath Lake Rotorua or Lake Taupō . The latest determination is 47 MW. The hydrothermal system that feeds still active geothermal features on

1924-547: The north of Lake Rotomahana in Waikanapanapa Valley but this was exhumed during the Tarawera eruption. After the eruption, water flowed into the new Green Lake crater, which was given the same name as the older lake. Other pre-eruption lakes and lakelets about Lake Rotomahana included Lakes Rotomakariri, Rangipakaru, Ruahoata and Wairake. The shape, location and orientation of Lake Makariri in Cole, 1970 (cited herein)

1976-510: The post eruption crater (and lake) is where the old Lake Rotomakariri was, part of the vent is likely to have been under it. However one interpretation of Hochstetter's original 1859 map's coordinates used to conjecture that some of the White Terrace might be buried rather than destroyed, would have put some of the old Lake Rotmakariri covered under a built up new Rotomahana crater rim today. Such an interpretation does not fit that well with

2028-434: The rhyolite appears to be a product of melting of crustal sedimentary rock. Water vapor plays an important role in lowering the melting point of silicic rock, and some rhyolitic magmas may have a water content as high as 7–8 weight percent. High-silica rhyolite (HSR), with a silica content of 75 to 77·8% SiO 2 , forms a distinctive subgroup within the rhyolites. HSRs are the most evolved of all igneous rocks, with

2080-576: The start of the 20th century: at the St. Andrew Strait volcano in Papua New Guinea and Novarupta volcano in Alaska as well as at Chaitén and Cordón Caulle volcanoes in southern Chile . The eruption of Novarupta in 1912 was the largest volcanic eruption of the 20th century, and began with explosive volcanism that later transitioned to effusive volcanism and the formation of a rhyolite dome in

2132-459: The subsurface. It is generally light in color due to its low content of mafic minerals, and it is typically very fine-grained ( aphanitic ) or glassy . An extrusive igneous rock is classified as rhyolite when quartz constitutes 20% to 60% by volume of its total content of quartz, alkali feldspar , and plagioclase ( QAPF ) and alkali feldspar makes up 35% to 90% of its total feldspar content. Feldspathoids are not present. This makes rhyolite

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2184-446: The terraces lay in their surveyed locations. Later Hochstetter survey research refined the Pink, Black and White Terrace locations. The issue of whether any of the terraces remain continues to remain unresolved. A small lake, Green Lake, lies close to the eastern shore of Lake Rotomahana at 38°15′00″S 176°28′18″E  /  38.25000°S 176.47167°E  / -38.25000; 176.47167 . It should not be confused by

2236-420: The terraces or sections of them survived in their original locations. The 2017- research relied on the journals of German-Austrian geologist Ferdinand von Hochstetter , who visited the lake in 1859. Hochstetter's journals are the only known survey of the terraces before the eruption. Using Hochstetter's field diaries and compass data, a team of New Zealand researchers identified a location where they believe

2288-405: The time since the 1314 ± 12 CE Kaharoa eruption of Mount Tarawera. The eruption process which was basaltic deposited muddy material widely and many metres thick especially to the northeast. One or other of the lakes that existed before the eruption is the likely origin of shells of water-snails found, in a sample of fresh ash from Tauranga , and in an ash sample from Cape Runaway . Essentially

2340-450: The vent. Rhyolite magmas can be produced by igneous differentiation of a more mafic (silica-poor) magma, through fractional crystallization or by assimilation of melted crustal rock ( anatexis ). Associations of andesites , dacites , and rhyolites in similar tectonic settings and with similar chemistry suggests that the rhyolite members were formed by differentiation of mantle-derived basaltic magmas at shallow depths. In other cases,

2392-655: The way to rhyolite, and about 8% of the volcanic rock in Iceland is rhyolite. However, this is unusual, and the Hawaiian Islands (for example) have no known occurrences of rhyolite. The alkaline magmas of volcanic ocean islands will very occasionally differentiate all the way to peralkaline rhyolites, but differentiation usually ends with trachyte . Small volumes of rhyolite are sometimes erupted in association with flood basalts , late in their history and where central volcanic complexes develop. The name rhyolite

2444-499: Was called Lake Rotomakariri . After the eruption a new Lake Rotomakariri to its east briefly existed before being incorporated by lake level rise into the present lake. The now lake floor was mostly dry when surveyed in the period 1886 to 1888 after the eruption, and it is possible to match these observations with current geolocated hydrophonic findings. High quality pictures of the old Lake Rotomahana and associated tourist attractions were widely available in Europe by 1875. Following

2496-405: Was in a swampy vegetated location and the village of Waingōngongo on the lake shore was destroyed in the 1886 eruption with the loss of 19 lives. The first official survey was done in 1887 after the eruption and this mapping showed a new cold water lake, also called Rotomakariri well to the east of the previous lake, in a new Rotomahana crater. Pictures of this new and temporary Lake Rotomakariri in

2548-657: Was introduced into geology in 1860 by the German traveler and geologist Ferdinand von Richthofen from the Greek word rhýax ("a stream of lava") and the rock name suffix "-lite". In North American pre-historic times , rhyolite was quarried extensively in what is now eastern Pennsylvania . Among the leading quarries was the Carbaugh Run Rhyolite Quarry Site in Adams County . Rhyolite

2600-567: Was mined there starting 11,500 years ago. Tons of rhyolite were traded across the Delmarva Peninsula , because the rhyolite kept a sharp point when knapped and was used to make spear points and arrowheads. Obsidian is usually of rhyolitic composition, and it has been used for tools since prehistoric times. Obsidian scalpels have been investigated for use in delicate surgery. Pumice, also typically of rhyolitic composition, finds important uses as an abrasive , in concrete , and as

2652-411: Was not understood until many years later. Lake Rotomahana Lake Rotomahana is an 890-hectare (2,200-acre) lake in northern New Zealand , located 20 kilometres to the south-east of Rotorua . It is immediately south-west of the dormant volcano Mount Tarawera , and its geography was substantially altered by a major 1886 eruption of Mount Tarawera . Along with the mountain, it lies within

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2704-435: Was to the east of the White Terrace and the old Lake Rotomahana, between Lake Rotomahana and Mount Tarawera. The shape of the lake varies from the original 1859 map in later versions of the same map, and it seems most likely that the old Lake Rotomakariri was an ovoid orientated north-south as this was how it was sketched in 1859 and immediately after the eruption. It drained via a creek called Awapurohe   ( Māori ) into

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