The Waimangu Volcanic Rift Valley is the hydrothermal system created on 10 June 1886 by the volcanic eruption of Mount Tarawera, on the North Island of New Zealand. It encompasses Lake Rotomahana, the site of the Pink and White Terraces, as well as the location of the Waimangu Geyser, which was active from 1900 to 1904. The area has been increasingly accessible as a tourist attraction and contains Frying Pan Lake, which is the largest hot spring in the world, and the steaming and usually pale blue Inferno Crater Lake, the largest geyser-like feature in the world although the geyser itself cannot be seen since it plays at the bottom of the lake.
Waimangu is a Māori-language word meaning "black water". This name comes from the water that was thrown up by the Waimangu Geyser, which was black with mud and rocks.
From the 1890s onwards, the valley has gradually been re-populated naturally by plants ranging from hot water-loving algae and bacteria to mosses and many species of native ferns, shrubs and trees. These in turn support native birdlife including kererū, tūī, shining cuckoo, fantail, bellbird, and pūkeko, as well as introduced bird species such as mynah, magpie, finch and sparrow. A population of black swan thrives in the lower parts of the valley and on Lake Rotomahana. According to local guides, these have been introduced to the region from Western Australia by George Edward Grey in the 19th century along with wallaby.
As a rare eco-system completely naturally re-established following a volcanic eruption, Waimangu is protected as a Scenic Reserve, administered by the Department of Conservation NZ. The developing local native forest is the only current New Zealand instance of vegetation re-establishing from complete devastation without any human influence such as planting. Many of Waimangu's geothermal features are ranked as Category A – extremely important, of international significance.
History
The largest volcanic eruption in the past 700 years in New Zealand, the 1886 Mount Tarawera eruption, created the geo-thermal area of the Waimangu Volcanic Rift Valley. The valley lies at the south-western end of the rift created in this one-day eruption. All vegetation in the Waimangu Valley was completely destroyed by the eruption and the area was covered in mud and volcanic ash on average thick.
Over the decade following the Mount Tarawera eruption, hydrothermal surface activity and geothermal features permanently established themselves in the Waimangu Valley, even though no such activity had been reported there before 1886. Plant life slowly re-established itself around the turn of the century as the new soil began to settle and stabilise.
The first significant hydrothermal feature of the area was the Waimangu Geyser, active from 1900 to 1904. Over the course of the first two decades of the 20th century, several events shaped the area around Echo Crater and Inferno Crater. Eruptions in 1915 and 1917 enlarged Echo Crater. The craters formed by the latter eruption filled up to become Frying Pan Lake by mid 1918. Further smaller eruptions continued throughout the 20th century, with the most recent one in May 1981 in the Raupo Pond Crater destroying the Mud Rift created there in 1906.
Geothermal and Hydrothermal Features
The stretch of the Waimangu Volcanic Rift Valley running from Southern Crater to the shores of Lake Rotomahana has been a hotspot of geothermal and hydrothermal activity since the 1886 Mount Tarawera eruption, and contains the three lake-filled craters Southern Crater, Echo Crater, and Inferno Crater, as well as the bush-clad Raupo Pond Crater, Fairy Crater and Black Crater.
The Southern Crater was formed by the 1886 Mount Tarawera eruption and has not been notably active since. Its floor is filled by the shallow Emerald Pool, a cold water lake of mostly rainwater. The lake's water is usually a brown colour, but can vary depending on the state of the plants growing in it. Red aquatic fern growth is sometimes present.
A short distance northeast lies Echo Crater, the biggest crater of the area, filled with the steaming-hot Frying Pan Lake, which is the largest hot spring in the world. The lake has an average depth of and covers . The average temperature of its acidic (pH 3.5) water is and the lake's overflow is the source of Waimangu Stream (Hot Water Creek) flowing through the valley and into Lake Rotomahana.