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Volcanic Landscapes of New Zealand 291

between magmatic fluids and lake water that
often produces lahars. The Crater Lake is located
over the actual vent of the volcano and is
especially important. Twice last century Crater
Lake was completely emptied during eruptive
episodes. On both occasions, in 1945 and 1995,
bridges were destroyed and damaged. When the
lake also partially emptied on 24 December 1953
the resulting lahar washed away a rail bridge at
Tangiwai killing 151 of the 285 passengers and
crew aboard a passing express train. This was one
of New Zealand’s worst tragedies, and preventing
a recurrence of it has been a major focus of
government agencies since that time.
The Tongariro andesitic volcanic complex
(which includes Ngauruhoe) first erupted about
270,000 years ago (Smithsonian Institute, 2010).
Eruptions from the 12 or more composite cones
making up the complex have continued
intermittently since. The youngest vent on the
Tongariro volcano is Mt Ngauruhoe (Figure 19.3),
Figure 19.2 Map of the Taupo Volcanic Zone which first erupted about 2500 years ago and last
century was the most active volcano in New
Zealand, with frequent eruptions no more than
Mt Ruapehu (2797m) lies at the southern end of nine years apart although its last eruption was in
the zone and is one of the most active volcanoes 1975. Other than from the Ngauruhoe vent, Mt
in the world (Keys and Green, 2004). It began Tongariro’s last eruption was in 1896 from the
erupting at least 250,000 years ago, and in recent active Te Maari crater. Mt Ngauruhoe is a
recorded history major eruptions have been about composite or stratovolcano composed of layered
50 years apart (1895, 1945 and 1995–1996). lava flows and volcanic ash and debris. Some
Minor eruptions are much more frequent, with at others, such as Mt Tarawera (near Rotorua), are
least 60 since 1945. Some of the minor eruptions dome-shaped and composed largely of viscous
in the 1970s generated small ash falls and lahars lava which does not flow readily. Another readily
(mudflows) that damaged skifields and disrupted identifiable landform resulting from extreme
other forms of outdoor recreation. Between major volcanism shape is the collapsed volcanic centre
eruptions a warm acidic crater lake forms, fed by known as a caldera (see Chapter 1). These are
melting snow. Where a major eruption has often filled by lakes such as Lake Taupo and Lake
deposited a tephra dam across the lake’s outlet this Rotorua. Ketetahi Springs, on the side of Mt
may collapse after the lake has refilled and risen Tongariro, is a collection of hot mineral springs
above its normal outlet level, and the outrush of and steam vents (fumeroles) and there are more of
water can cause a large lahar. In 2000, an early these throughout the Central Plateau region.
warning system (ERLAWS) was installed on the Further fumerolic activity is responsible for the
mountain to detect such a collapse and alert the tiny steam plume sometimes visible above Mt
relevant authorities. Ngauruhoe and for the activity near the Red
Volcanic processes can be seen in action in Crater.
this region and studied as a ‘natural laboratory’. To the west is Mt Taranaki/Egmont. Formerly
The Ruapehu Crater Lake is one of two such known as Mt Egmont, this stratovolcano last
lakes (together with Kelut in Java) that are erupted about 200 years ago at the end of an
regarded as classic case studies of the interaction eight-eruption cycle that had occurred over the

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