Lady Knox Geyser, Induced geyser in Waiotapu, Waikato region, New Zealand

Lady Knox Geyser is an induced geyser beside the Wai-O-Tapu Thermal Wonderland visitor centre, about 26 km south-southeast of Rotorua. Its vent is ringed by a rough, pale grey-white cone of silica and pumice, and eruptions send a dense white column of water and steam up to 20 m high, with steam billowing to one side against the tree-covered slope behind.

In 1901 New Zealand's first open prison was set up at Waiotapu. Prisoners washing clothes there found the hot spring erupted when soap was added. The camp's head, Scanlon, narrowed the vent with a steel pipe and ringed it with pumice, raising jets to about 17 m; the New Zealand Herald reported the Northland Geyser in December 1906.

The geyser was first presented to the public as the Northland Geyser in a New Zealand Herald article of 6 December 1906, and later appeared in tourist publications as the Waiotapu Geyser. Its present name honours Lady Constance Knox, daughter of Uchter Knox, 15th Governor of New Zealand. Because it was discovered in the early 20th century, it has no Māori name, unlike almost every other thermal feature in the country.

The geyser is induced to erupt daily at 10:15 am, when a surfactant is dropped into the vent, so time your visit around that demonstration. The visible spout is a cone of rocks and built-up silica at the spring's base, and eruptions can last over an hour depending on the weather. It lies near the visitor centre of Wai-O-Tapu Thermal Wonderland, about 26 km south-southeast of Rotorua.

Unlike other geysers in the region, this one is triggered by human intervention rather than purely natural geological processes. This management creates a predictable display that sets it apart from wild, unpredictable geysers elsewhere.