Twenty minutes out of Rotorua on the Tarawera road lies picturesque Tikitapu. An undulating track meanders around the lake and it takes 1.5 hours to complete if you stop to admire the stunning views.
The scenery is 20, 000 years in the making and each hill and cliff face marks a significant volcanic event.
The hill that looks like a cuddly neck collar worn on long haul flights exploded into life 21000 years ago and is a rhyolite dome. Rhyollite is a thick viscous lava that melts at around 800 degrees celsius. It is simply referred to as North Dome.
Smooth and rounded or a bit crumpled.
Depends on which side of the lake you find yourself.
North Dome on the eastern shore has a beautifully rounded sculptured look. The lava flows appear this way because they have been liberally dusted with tephra (literally anything that falls from the sky) Dutch masters used the same technique, adding layers of paint till they got it right.
It is a slightly different story on the other side of the lake. The lava front cooled and solidified forcing the rest to back up and crumple leaving a noticeable rib structure more typical of rhyolite flows. This happened about 18000 years ago.
Tikitapu lies on the fringe of the Okataina volcanic centre.
Not far away, Mount Tarawerawas the scene of New Zealand’s most violent eruption in the last 500 years.
A rhyolitic dome split apart with very little warning. Earthquake tremors were first felt in Rototrua about 12.30am on 10 June 1886. Around 2am basalt lava rather than the usual rhyolite began erupting from the central dome of Mount Tarawera.
Two hours later pyroclastic eruptions were occurring on Taraweras three main peaks.
Better than a selfie
This work was painted by Charles Bloomfield who was renowned for his meticulous attention to detail. We can be reasonably certain this is an accurate representation of events
Towards the right of the painting Bloomfield has caught the moment basaltic lava at over 1000 degrees Celsius came in contact with the hydrothermal system underneath the old lake Rotomahana.
Like dropping water on a BBQ hotplate with gas turned up max the instantaneous production of colossal volumes of steam resulted in a phreatomagmaticexplosion.
What goes up must come down. The column of scoria ash mud and steam reached a height of 10 kilometres .
The catastrophic collapse of this column would have projected hurricane speed surges of scalding hot debris outwards from the base destroying everything in its path
New Zealand Journal of Geology and Geophysics
I. A. Nairn (1979) Rotomahana—Waimangu eruption, 1886: base surge and basalt magma, New Zealand Journal of Geology and Geophysics, 22:3, 363-378, DOI: 10.1080/00288306.1979.10424105 To link to this article: https://doi.org/10.1080/00288306.1979.10424105
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