Waimangu Valley and Mount Tarawera today.
The Okataiana Volcanic centre lies in the Taupo volcanic zone and there have been several huge explosions in the last 250,000 years. After each eruption the area surrounding the vent collapsed filling the space left by the escaped magma. A large caldera roughly 18km by 25km has formed and less violent eruptions over the last 40,000 years have filled its floor with a mixture of pumice. lava flows and lava domes.
Tarawera volcano had four major eruptions between 18,000 and 800 years ago. The 1886 eruption which formed the Waimangu valley was by comparison a small event but is still the largest in European times. A rift 18 km long opened up in the space of a few hours. Huge volumes of molten basaltic magma and mud resulting from the explosion of the hydrothernal system under Lake Rotomahana were ejected. The eruption destroyed the famous pink and white terraces. Seven small villages in the vicinity of the lake were destroyed with the loss of 120 lives.
Feaures of the valley and the eruption of Mount Tarawere that brought it into existence
Waimangu Volcanic Valley leaflets, author Prof RF Keam, Physics Department, University of Auckland.