Before the eruption of Tarawera:
The Okataina volcanic center, with a rhyolitic dominance, is surrounded by extensive ignimbrite and layers of pyroclastic materials produced in multiple eruptions formative calderas. Many craters and lava domes form a northeast / southwest line belonging to volcanic complex Haroharo and Tarawera.
The caldera Haroharo, 16km of 26, gradually formed between 300,000 years ago and 50,000 years. Lava domes occupy a part of the caldera.
The complex Tarawera, south of the center Okataina, consists of 11 domes of rhyolitic lava and flows associated. Their dating ranges between 15,000 and there are 800 years.
The volcanic center Okataina and Tarawera eruption fissure of 1886 - a click to enlarge - Doc. http://users.skynet.be/etna/NZ/Tarawera.htm
The eruption of Tarawera in 1886:
Since the year 1310, when occurred the Kaharoa eruption of VEI 5, Mount Tarawera was "calm" ...
On 1 June 1886, the waters of Lake Rotomahana are troubled by strange waves. A local Maori priest interpreted the phenomenon as the appearance of a spirit -canoë representing the harbinger of a terrible future event ... legendary interpretation conveyed by tourists of the time.
At 0:30 on June 10, local residents were awakened by violent tremors marking the start of the eruption.
The initial phase is phreatomagmatic type, resulting from the rise of a basaltic magma - different from the other eruptions with rhyolitic magma - and he met the groundwater at a depth of 300 meters below surface.
At 1:30, the side of Wahanga dome explodes, opening a crack. The opening step by step and the expansion of the eruptive fissure resulting in a series of 13 craters through the Tarawera dome complex.
The main Plinian phase Plinian generates an eruptive column about 30 kilometers high, according to the analysis of deposits, and could have stopped after four hours. A study of deposits nearby the crack corroborates the testimonies of several smaller eruption columns feeding the main Plinian column. We now think that vents 4 craters, located in an area between the tuff cone Ruawahia and the southwest portion of the Tarawera Dome, contributed to the establishment of the Plinian column. During the Plinian phase, lower vents in a section northeast of the crack had a strombolian activity.
At the end of the Plinian phase, a brief phreatomagmatic phase took place, perhaps as a result of a further collapse of the summit of the magma column in the groundwater.
This eruption, described by the GVP of VEI 5, opened a rift 17 km long across the top of the mountain, through the Lake Rotomahana and into the Waimangu Valley. A mixture of steam and finely pulverized rock, known as the "Mud of Roromahana" formed by the phreatic / phreatomagmatic massive eruptions, has spread as a base surge over 4-6 km, causing destruction and death. Although some deaths are directly caused by this surge, most were attributed to the collapse of roofs caused by the accumulation of wet ash. Villages were destroyed and instead the site of Pink and White terraces, a crater deep more 100 meters open.
Steam eruptions continued for several months in this crater, but in fifteen years, a new Rotomahana lake was formed, larger than the previous. The chain of craters in the Waimangu area became the seat of new geothermal structures, and the largest hot spring in New Zealand, Frying Pan Lake.
- GNS - Okataina Volcanic Centre/ Mt Tarawera Volcano
- Te Ara – Historic volcanic activity – Tarawera
- Global Volcanism Program – Okataina