The Horohoro Fault is in the old

Taupō Rift The Taupō Rift is the seismically active rift valley containing the Taupō Volcanic Zone, central North Island of New Zealand. Geology The Taupō Rift (Taupo Rift) is a intra-arc continental rift resulting from an oblique convergence in the H ...

of the central

North Island The North Island ( , 'the fish of Māui', historically New Ulster) is one of the two main islands of New Zealand, islands of New Zealand, separated from the larger but less populous South Island by Cook Strait. With an area of , it is the List ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

and is associated with the spectacular Horohoro Cliffs.

Geology

Just south of

Lake Rotorua Lake Rotorua () is the second largest lake in the North Island of New Zealand by surface area, and covers 79.8 km2. With a mean depth of only 10 metres it is considerably smaller than nearby Lake Tarawera in terms of volume of water. It i ...

, Horohoro mountain, a

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

dome, has very high cliffs in an apparent fault scarp that defines the western edge of the lower lying Paeroa Garben and its northern Kapenga Caldera. The Paeroa Garben's eastern edge is defined by the

Paeroa Fault The Paeroa Fault is a seismically active area in the Taupō District, Waikato Region of the central North Island of New Zealand. Geology North of Lake Taupō, volcanic ignimbrite at least thick, and called the Paeroa Ignimbrite (dated to 339 ...

. The cliffs are composed of Mamaku ignimbrite from the

Rotorua Caldera The Rotorua Caldera is a large rhyolitic caldera that is filled by Lake Rotorua. It was formed by an eruption 240,000 years ago that produced extensive Pyroclastic rock, pyroclastic deposits. Smaller eruptions have occurred in the caldera since ...

eruption and older ignimbrites and Rotorua rhyolite. This fault area of the

is controversial as the components of historic tectonic and volcanic contribution have led to debate. Some authors have also extended and widened the definition of the Ngakuru Graben, which is to the south, during this debate. The northern portion of the fault for the last 20,000 years is displacing at a low rate of up to 0.2 mm/yr but it is unknown if the southern portion is active. The far northern portion passes through the Hemo Gorge which may have been created by a flood event soon after the creation of the Rotorua caldera, with only later drainage of the caldera being established towards the Bay of Plenty. What is known is that the fault has displaced historically at a much higher rate before the last Taupō

Hatepe eruption The Hatepe eruption, named for the Hatepe Plinian pumice tephra layer, sometimes referred to as the Taupō eruption or Horomatangi Reef Unit Y eruption, is dated to 232 CE ± 10 and was Taupō Volcano's most recent major eruption. It is ...

. It has been speculated that just after the paired

and Ohakuri Caldera eruptive sequences of 240,000 years ago when the magma mush had been erupted the garben sunk by over . It has also been speculated that the modern

s far west edge is actually this fault line although most think this is more to the east, along the line of the Paeroa Fault. It has also been speculated that the northern part of the fault is actually the western edge of the Kapenga Caldera with the Horohoro dome in its rim.

Risks

This intra-rift fault has been estimated to have single event earthquakes in its northern portion up to about 6.5 Mw every 5000 to 7000 years. The time of the last fault rupture was after 8000 years ago but before the

References

{{Seismic faults of New Zealand Seismic faults of New Zealand Taupō Volcanic Zone