Waiotapu - page 2
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Leaving the mud pots and collapse craters behind for now the trail is heading towards absolute highlights of Waiotapu, the Champagne Pool and its large discharge areas Artist's Palette and Primrose Terrace. From the observation platform in the north Artist's Palette can be seen in all its splendour.
Directly in front of the viewpoint a somewhat smaller circular hot spring shows up, which is more or less a miniature version of Champagne Pool, even if the reddish rim is slightly on the small side. In the annual monitoring reports of the Waikato Regional Council this spring is called Foreground Pool.
In the background right of the picture, Artist's Palette merges with Primrose Terrace. A boardwalk runs across this very section in direction of Champagne Pool. On the far (southeast) side at some distance to the boardwalk, Jean Batten Geyser is to be found. This is another feature which was shown in the old tour pamphlet but is missing in the new one. Also the wooden name sign in front of the geyser has been removed. Guided by the current pamphlet instead of my own keyword list, I missed to take a photo of the geyser vent. It is a relatively small crater in the sinter surfarce on the far side of a somewhat larger circular pool, which is sometimes empty but often yellow hued by sulfur deposits. Jean Batten Geyser plays up to 3 m (10 feet) high at irregular intervals, but it is considered to be dormant, probably since the early 2000s. Necessary prerequisites for its activity are strong easterly or south-easterly winds because they force Champangne Pool to discharge to the west instead to the southeast over Primrose Terrace. These conditions in turn keep the cold runoff of Champagne Pool away form the geyser vent and prevent the feature from being cooled below trigger temperature. The geyser was named for the Rotorua born aviatrix Jean Gardner Batten, who made some record-breaking solo flights across the world in the 1930s.
Scattered about Artist's Palette are a couple of further small spings, one of them is a geyser. Approximately 30 m (100 ft) northeast of Champagne Pool and only 10 m (33 ft) away from the boardwalk, NW Boardwalk Geyser appears as a circular, flat funnel, ca. 5 m (16 ft) in diameter, with a deep vent in centre. The Waikato Regional Council Technical Report 2020/04, Sinter-forming springs and geysers of the Waikato region, states eruptions of NW Boardwalk Geyser up to a height of 3 metres (10 feet) in the mid-1990s. The last activity was recorded for 2002.
On the way from Artist's Palette overview to Champagne Pool a junction to the left leads to Te Waiāriki o Mahuika (The Hot Spring of Mahuika). A high sulfur content tints the shallow pool of the fire goddess Mahuika greenish-yellow.
Along the eastern border of Artist's Palette the boardwalk proceeds to Champagne Pool. The name refers to the beige-green coloured water combined with sparkling carbon dioxide bubbles arising from the depth. Champagne Pool was formed over 900 years ago by hydrothermal eruption and is approximately 70 m (230 feet) in diameter, 62 m (203 feet) deep and has an estimated volume of 50,000 m3. It represents not only the largest, but also the central and highest situated hot spring in the inner Waiotapu area, like a spider in the web. According to what is known, Champagne Pool features the most direct conduit to the 230 °C (446 °F) hot aquifer in a depth of probably more than 450 m (1500 feet). Slightly acidic water (pH 5.5) enters the pool from the aquifer and cools down during ascent to a surface temperature of 74 °C (165 °F). This is still hot enough to shroud the large spring on most days in dense steam and makes it difficult to photograph.
The chemical richness of Champagne Pool is in no way inferior to a medieval alchemist's laboratory. Remarkable quantities are present of the rare metals arsenic, antimony, thallium, mercury, gold, and silver, together with the more common sodium, lithium, iron, manganese, boron, magnesium, calcium, chlorine and the ubiquitous sulfur, silicon, oxygen, nitrogen, carbon and hydrogen. With one another they form a huge number of minerals, of which the visually most conspicuous ones, the yellowish-green orpiment (As2S3), the intensely scarlet to brick-red cinnabar (HgS), and the bright red stibnite (Sb2S3) together with carlinite (Tl2S) and silica are responsible for the vibrant tangerine hued subaqueous rim. Moreover, significant amounts of gold (about 80 ppm) and silver (about 175 ppm) are included in this layer which is most prominent on the north and east sides of the pool.
The exciting chemistry of Champagne Pool is complemented by no less fascinating microbial life forms. In 1999, Joseph M. González et al. described a new, extremely thermophilic archaeon from Champagne Pool and named it after the finding place Thermococcus waiotapuensis (Archives of Microbiology 172, 95–101). However, this should not hide the fact that the giant hot spring, due to its high content in arsenic compounds, is an hostile environment even to robust thermophilic microbes. Compared to most other hot springs only very few species with few specimens have been found, for example archaea from the genera Sulfolobus, Thermofilum, and Thermococcus as well as bacteria from the genera Sulfurihydrogenibium, Thermoanaerobacter, Nevskia, and Paracoccus (A. Hetzer et al.; Microbial life in Champagne Pool, a geothermal spring in Waiotapu, New Zealand, Springer 2007).
Nevertheless, those microbiological communities are capable of adapting to the toxic conditions and in turn cause changes to the water chemistry, for example by eating (metabolising) inorganic arsenic compounds such as arsenite and transforming them to organic forms by adding hydrocarbon groups. A prominent example of a thermophilic bacterium tolerant to relatively high concentrations of arsenic and antimony compounds is Venenivibrio stagnispumantis from the order Aquificae, discovered in 2005 by Adrian Hetzer et al. It represents not only a new species, but also a new genus. The name can be translated as "The vibrio bacterium of poison from the bubbling pool", meaning Champagne Pool (A. Hetzer et al.; Venenivibrio stagnispumantis gen. nov., sp. nov., a thermophilic hydrogen-oxidizing bacterium isolated from Champagne Pool, Waiotapu, New Zealand, International Journal of Systematic and Evolutionary Microbiology 58, 2008).
Over the centuries Champagne Pool covered with its silica rich discharge water over 12,000 m2 with cream coloured sinter and formed the currently largest open sinter terrace of New Zealand, the Primrose Terrace. Only the flooded Pink and White Terraces in Waimangu had a larger extension. Due to its dimensions Primrose Terrace is hard to overlook all at once. This is best done from a viewpoint on the hill near Wāhi Tapu (Sacred Place).
From up close its dimensions are hard to estimate, but the structural details of the scaled sinter catch the eye.
Primrose Terrace terminates at Te Rere Ārai Mārena (The Waterfall of the Wedding Veil). The English name Bridal Veil Falls is the direct equivalent.
The last hot spring-related stop on the second loop trail, which connects the points of interest between Champagne Pool and Te Rere Ārai Mārena, is the Alum Cliffs overlook. From there most of the area can be seen which is accessible by the third loop trail. The Alum Cliffs are walls of hydrothermal explosion craters. Alum (aluminium sulfate) and other whitish salts are deposited on the cliffs by percolating water.
The bottom of the large crater directly in front of the viewpoint is filled by an unnamed, pale green lakelet, a hot spring which hides a special feature. In 1954, Edward F. Loyd discovered "black sulfur globules [that] had been erupted from spring N85/6/73 at the Alum Cliffs" (E.F. Lloyd, The hot springs and hydrothermal eruptions of Waiotapu, New Zealand Journal of Geology and Geophysics, 1959). Natural black sulfur is very rare in New Zealand, however, it had been found before in Echo Lake, a few hundred meters east of the Alum Cliff crater outside the Waiotapu tourist area.
Unfortunately, the trail from Te Rere Ārai Mārena to the crater spring at Alum Cliffs was closed during our visit on 19th November 2019. The current tour pamphlet gives no indication that one could miss something on that section of the trail, but the old pamphlet revealed that Waiotapu Geyser is located in the closed area. Very sad because therefore we missed to see a further geyser at Waiotapu. It is only a small one, playing from a little opening in the sinter up to one metre (3 feet) high at seemingly irregular intervals. Fifteen or twenty years ago the eruptions of Waiotapu Geyser must have been much stronger since Ashley D. Cody listed in Geodiversity of geothermal fields in the Taupo Volcanic Zone from 2007 a typical height of 2.5 m (8 feet). On the right (west) side of the vent a tiny circular opening in the sinter acts as an indicator by discharging some water prior to an eruption. Poyan Nikrou, Juliet Newson, and Robert McKibbin investigated the geyser's behaviour and possible dependencies of the eruptions on external factors in 2010 and 2011. They recorded active periods lasting between 1 and 9 days, during which the geyser erupted 2 to 4 times a day for about 10 minutes each. Active periods were interupted by dormancies from half a day up to 2 weeks. The authors found a significant dependency of geyser activity on air pressure and possibly on rainfall, whereas air temperature or seismic activity seemed to have no influence (P. Nikrou, J. Newson, R. McKibbin; Time series analysis of selected geothermal spring temperature recordings, Waikato Regional Council Technical Report 2013/17).
Edward F. Lloyd described two further small geysers, N85/6/133 and 134, outside the tourist area in a gully to the west of the old Waiotapu Hotel, a location which today is west of the current Wai-O-Tapu parking lot. One of them is the usually 30 cm (1 foot) high playing Hakereteke Geyser, the only acidic sinter-depositing geyser in New Zealand.
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