Volcanic terraces grow in bath of silica-rich hot water

Raewyn Hill looks out over the man-made Wairakei Terraces. Picture / Alan Gibson

One hundred and twenty years after an eruption destroyed the Pink and White Terraces, a new terrace is forming.

Covered by torrents of boiling hot geothermal water, it emanates a glow reminiscent of buried terraces at Lake Rotomahana.

Silica is gathering on an elegantly formed staircase flourishing under the flow of mineral-rich water piped from a geothermal power plant at Wairakei, near Taupo.

Renowned as one of the great natural wonders of the world, the Pink and White Terraces were destroyed when Mt Tarawera blew up in clouds of ash on June 10, 1886.

The Wairakei terraces, 80km from Mt Tarawera, are smaller than the original which inspired their creation but thanks to careful management of water temperature, level and speed of flow, they are starting to show some of the colour and form of their predecessors.

A geyser has been built behind the terraces and the geothermal water gushes out of it at 130C, cooling as it flows over the 8m terraces into a stream below.

The stream, which is still about 70C, had been diverted when the power plant was built in the 1950s but now flows along its natural path into the Waikato River.

The stream's name is Te Kiri o Hinekai, meaning "food for the skin of a woman" - a reference to the healing/cosmetic properties of the minerals in the water which turn it a beautiful shade of bluey-green.

The water [also] holds the key to the pinky-white silica deposits forming on the terraces, which were built in two stages, in 2001 and last year, as a tourism venture.

The company owners, Raewyn and Jim Hill, say the terraces are the first manmade ones of their type in the world.

"We say that nobody else was fool enough to do it," Jim joked last week.

Construction cost $1.5 million and involved a team of eight digging the layered terraces, at times by hand, and creating sculpted pools on each level.

Concrete was poured on the foundations of the first stage, which cover an area 50m x 70m, but was later removed when it was found that the silica did not stick.

For the second stage, measuring 30m x 50m, packed silica was applied on the base, and has helped the silica in the water stick.

Though just a year old, the terraces in this section are pure white in places and have whirlpool-shaped mounds of silica swirling in their pools.

"We've been surprised how quickly it's grown," Raewyn said.

She said the terraces were not intended as a replica of the Pink and White Terraces, which stood on Te Arawa land, but were reminiscent of both them and another set of terraces that once existed at Wairakei, which is home to Tuwharetoa.