Wai-O-Tapu is a geothermal field in the Waikato region of the North Island of New Zealand, south of Rotorua, where a crater pool 65 metres across rims itself in orange with sulphides of arsenic and antimony, its overflow paints terraces of silica and a pond the colour of lime, and a geyser is set off every morning with soap, walked on a loop of boardwalks through steam. The name means sacred waters, and the field lies on the volcanic zone that runs through the island, its ground riddled with craters, mud pools and vents; the Champagne Pool is the centre, a crater blown out 900 years ago and filled with water at 74 degrees that breathes strings of carbon dioxide like a glass of champagne, and the boardwalk carries the visitor to the rim, close enough that the warmth reaches the face, with the orange shelf around it an ore deposit forming in plain sight, gold and silver among the minerals it lays down. The overflow drains across the Artist's Palette, a shallow lake stained in bands, and down Primrose Terrace, the largest silica terrace in the country, where a film of hot water is still adding to the rock.
Lady Knox geyser plays at 10:15 each morning, when a warden explains the chemistry, tips surfactant into the vent to break the surface tension of the cold water lying on the hot, and within a minute the geyser foams over its cone and climbs into a jet up to 20 metres high that can keep going for an hour, a trick discovered by prisoners washing their clothes in the spring. The loop ends at the Devil's Bath, a crater pool of yellow-green water coloured by sulphur and ferrous salts, at its hardest under a high summer sun and flat grey under cloud, and in winter the steam off the hot water rolls across the pools and hides them as often as it shows them. Wai-O-Tapu is a chemistry set left on the boil, and the colours are the minerals coming out.