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Silica Terraces of Orakei Korako

A cache by YuGeo4 Send Message to Owner Message this owner
Hidden : 6/23/2009
Difficulty:
1 out of 5
Terrain:
1 out of 5

Size: Size: not chosen (not chosen)

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Silica Terraces of Orakei Korako

The posted co-ordinates will take you to a public carpark overlooking the Emerald Terrace,
a large example of a fault-stepped sinter terrace.


Geothermal Systems and Features

Orakei Korako (Maori for “The Place of Adorning”), is a highly active geothermal area most notable for its series of fault-stepped sinter terraces, located in a valley on the banks of the Waikato River in the Taupo Volcanic Zone, New Zealand. It is also known as “The Hidden Valley”.

The Taupo Volcanic Zone, located between Mt Ruapehu and White Island, contains almost 80 percent of New Zealand’s geothermal systems. The most famous of these is the Rotorua geothermal field, which contains over 1200 geothermal features. Other geothermal features occur in the Far North, the Hauraki Gulf, and in scattered hot springs in the North and South Islands.

A wide variety of geothermal features are formed by the discharge of heated water and steam at the Earth’s surface. The variety depends on fluid temperature, pressure, dissolved constituents and gas, composition and structure of the host rock, its permeability and the age of the geothermal system. The geothermal fluids rise to the surface as steam, superheated water, water below boiling point or mixtures. A wide range of gases and minerals can be emitted or precipitated during the discharge.

  • Discharge of brines creates hot springs some of which form relatively passive pools while others release large quantities of gas.
  • Geysers are formed when a pocket of groundwater accumulating and heating under pressure is finally heated to boiling point so that large volumes of steam are produced. This pushes up and out of the underground pocket carrying water with it. As it rises the pressure on it reduces so more and more steam is formed, until it ejects out at the surface as a column of steam and water. New Zealand is one of only seven countries in the world that has active geysers.
  • Fumaroles, or steam vents, and steam heated ground are formed where water boils underground so that only steam reaches the surface.
  • Boiling mud pools are created in places that have limited hot water but an abundant supply of steam and rock material of a type that breaks down into mud. Hydrogen sulphide gas (which creates the rotten egg smell common to thermal areas) in the steam reacts with oxygen generating sulphuric acid. This dissolves the surrounding rock into fine particles of silica and clay that mix with what little water there is to form the seething and bubbling mud pools.
  • Silica terraces and flats are formed over tens to thousands of years as hot geothermal waters flow out over the land, cooling and releasing silica and other minerals. New Zealand has had some of the largest silica terraces in the world, including the once famous Pink and White Terraces near Rotorua, which were considered to be the eighth wonder of the natural world until they were completely destroyed by a volcanic eruption of Mt Tarawera in 1886.

The History of Orakei Korako

From earliest times the Waikato Valley near Orakei Korako was occupied by Maori of the Ngati Tahu sub-tribe of Tuwharetoa. By the early 1800s the Maori population had congregated at Orakei Korako, probably attracted by the hot springs, which were used for cooking and bathing. The date when the Ngati Tahu vacated the valley to settle at other locations is not recorded, but it has been suggested that they left after the eruption of Mount Tarawera in 1886, when great changes are alleged to have occurred in the hot springs. By the turn of the century all but two families had moved from Orakei Korako.

The earliest known route from Rotorua to Taupo for early European travellers passed right through Orakei Korako, and it was the existing Maori who provided a dug out canoe for the river crossings. It was at this point in the early 1900s that the geothermal area was established as a visitor attraction. To transfer visitors across the then-swift Waikato River they used the dug out canoe, until in the 1930s a wire-strop and pulley system was erected across the river, and a punt with a guiding rudder was used to catch the flow and propel the punt to the other side.

The first proposal for power development at Orakei Korako was made in 1904, but it wasn’t until 1955 that the scheme was finally approved. By May 1960 an earth-filled dam, rising 49 metres above the original river level, was placed and consolidated. The filling of Lake Ohakuri began on 19 January 1961 and was completed in 14 days.

Two of the world’s largest geysers were drowned by the lake: Minginui Geyser, which was once observed erupting up to 90 metres high (equal to the world's tallest currently active geyser, Steamboat Geyser in Yellowstone National Park), and the Orakeikorako Geyser, which on occasion could erupt up to 55 metres, and also gave the whole region its name.


Orakei Korako Today

The lowest terrace at Orakei Korako is the jade-green Emerald Terrace, which is the largest of its kind in New Zealand. In peak wet conditions up to 20 million litres of silica-enriched water per day may flow over the terrace and into Lake Ohakuri.

The 20 metre thick Emerald Terrace continues 35 metres under the lake, which was formed for hydropower generation in 1961. This raised the Waikato River level by 18 metres at Orakei Korako, flooding approximately 200 alkaline hot springs and 70 geysers (or two thirds of the active thermal area). Some of these thermal features still discharge, with their presence evident as gas bubbles rising from the vents in the lake bed.

Despite the loss of so many of its thermal features under the artificial lake, Orakei Korako remains the largest geyser field in New Zealand, with up to 35 active geysers. The most famous of these is the Diamond Geyser, whose unpredictable eruptions can last from a few minutes to many hours, ejecting boiling water as high as nine metres.

The three terraces above the lakeside Emerald Terrace are great fault scarps formed by a massive earthquake in 131 AD, around the time when Lake Taupo (a supervolcano) was last erupting. They are mostly covered in hot water algae, or cyanobacteria, which grows in temperatures between 35-59 degrees Celsius, the colours dependent on the species, with green, yellow and black the most common.

At the base of the two lower terraces – named Rainbow and Cascade Terraces – are several small geysers, including the intermittently active Sapphire Geyser, and the Hochstetter Pool (named after Austrian pioneer geologist Ferdinand von Hochstetter, who visited the area in 1859), which erupted in November 1954 and played as a geyser until mid-1955, ceasing suddenly after swarms of subterranean earthquakes.

The third and largest great fault scarp in the valley is called the Golden Fleece Terrace (named Te Kapua by the Maori people, meaning “The Cloud”), which is five metres high and 40 metres long, with a beautiful white crystal-like sinter coating. At the base are numerous vents where geysers have come and gone over the years, with the most recent, Wairiri Geyser.

Atop this terrace is the Artist’s Palette, a 10,000m² silica sinter terrace covered with clear blue alkali chloride pools and irregularly erupting geysers. To one side of this topmost terrace a new geyser began to erupt in 2001, possibly the beginnings of a further terrace.

Also at Orakei Korako is the Ruatapu Cave, one of only two caves in the world known to exist in a geothermal field. The cave extends 45 metres, with a vertical drop of 23 metres, to a shallow pool of clear, sulfate-rich, warm acid water. (The pool’s chemical composition gives it the unique ability to clean jewellery.)

Another notable feature at Orakei Korako is the Soda Fountain, which burst into life in 1984 after a 17 year dormancy.

To the south of this feature, high atop a cliff above Lake Ohakuri, are three further geysers, Kurapai, Ellan Vannin and Benedix Washer Geysers, in an area not accessible to the public because it is too dangerous. Temperatures of 100 degrees Celsius have been recorded here just 100 to 150 mm below the ground. Of these geysers, Kurapai Geyser is the most significant, and can sometimes be seen erupting from across the lake in the visitor's centre.

The Orakei Korako geothermal system is now protected from further development.

Logging Requirements for this Earthcache

Please email the cache owners, the answers to the following questions and await confirmation before logging your find online. Do not post your answers online.

  1. In your own words, describe the physical appearance of the silica terrace seen across the river, its colours, what causes them, and how they were formed.
  2. On the information panel located at S38 28.447 E176 08.606, what is the name of terrace number #4?
  3. Name the four terraces located at Orakei Korako.
  4. Describe what is found at S38 28.445 E176 08.627. According to the sign, when was it last used?
  5. What major geological features were destroyed / extinguished in the sixties? What caused this?
  6. Please post online, a picture of yourself (if you so wish) with/or your GPS, with the Emerald Terrace clearly seen in the background. This is to record the seasonal changes in the appearance of the Emerald Terraces. Take this photo at or near S38 28.437 E176 08.639.

PLEASE, no night visits will be allowed... as you won't be able to see any of the terraces.
Failure to comply with the logging requirements may result in your log being deleted.


Some things you might see if you decide to cross over the lake (click on images to expand)

Orakei Korako Ferry Rainbow Terrace Map of Africa
Map of Africa Ruatapu Cave Ruatapu Cave Rainbow Terrace

Explicit permission has been granted for the placement of this Earthcache by the Guardians of Orakei Korako. Please be respectful of the environment while you enjoy your visit to this unique geothermal area.

Good Luck and Happy Earth Caching

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