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The New Zealand Volcanological Record is an annual summary of volcano
and geothermal observations from New Zealand's active and potentially
active volcanoes. It covers Raoul Island, Auckland, White Island, Okataina,
Rotorua, Taupo, Egmont (Taranaki), Tongariro-Ngauruhoe, and Ruapehu, and
includes visual, seismic, geodetic, geochemical, geothermal and geological
observations.
Introduction
The highlight of 1996 was a series of large ash eruptions at
Ruapehu in June and July, with minor eruptive activity continuing until
September. These eruptions had a significant affect on local and regional
infrastructure, including the closure of Auckland International Airport,
though many had learned from the 1995 eruptions and were better prepared
this time. A special Ruapehu eruption section highlights some of the observations
and work carried out.
White Island was relatively quiet during the year, with minor ash and steam eruptions in late-March the only notable activity. Self potential and audio magneto telluric measurements were made during the year and are reported. The other volcanic centres were quiet with no significant seismic activity, ground deformation or chemical changes.
Taupo Volcanic Zone Location Map
Taupo Volcanic Zone Seismograph
Sites (82kb)
1996 Ruapehu Eruption Special Section
Eruption Narrative
Lahars
Volcano-Seismic
Activity (307kb)
Distal Ash Falls
Raoul Island
Raoul Island (29o14'S; 177o 55'E), with an area
of about 30 km2, is the northernmost island of the Kermadec
Group. Raoul is an active volcano, with witnessed eruptions in 1814, 1870
and 1964. The dominant structural and physiographic features are the Raoul
and Denham Bay calderas, both formed during large eruptions of dacite
pumice over the last 4000 years. The regularly monitored Blue and Green
lakes lie within the Raoul caldera.
Crater Lakes, Temperatures, and Deformation
Auckland Volcanic Field
The Auckland Volcanic Field covers an area of about 640 km2,
virtually coincident with the Auckland City metropolis. It is a monogenetic
basaltic field comprising 49 recognised volcanic centres. Activity has
occurred over at least the last 50,000 years. The last eruption, which
produced the largest volume of material and formed Rangitoto Island, ended
600-1000 years ago.
Auckland Seismicity
(28kb)
White Island
White Island (37o 31'S; 177o 11'E) is the emergent
summit of a large submarine volcanic edifice, which lies about 50 km off
the Bay of Plenty coast. This 2 x 2.4 km uninhabited island has been in
a state of continuous sulfataric and fumarolic activity, with intermittent
minor steam, tephra and magmatic eruptions since 1826 when the first recorded
visits by Europeans were made. The latest eruptive episode commenced in
February 1986 and continued until early 1992. Minor activity occurred
later in 1992 and during 1993-94.
White Island Regional Seismicity
(65kb)
Eruption Observations, Seismicity and Crater Geomorphology
Magnetic Surveying
Self-Potential and Audio-Magnetotelluric Survey
Rotorua Volcanic Centre
The Rotorua Volcanic Centre consists of a large topographic basin, the
Rotorua Caldera, about 20 km across, containing Lake Rotorua. The caldera
boundary is marked by a roughly circular fault scarp to the south, east
and north. To the northwest the ground surface is gently down-warped into
the basin. The last ignimbrite eruption was about 140 000 years BP. Younger
rhyolite lava domes have been extruded onto the caldera floor.
Rotorua Area Seismicity (77kb)
Okataina Volcanic Centre
Okataina Volcanic Centre lies east of Rotorua and includes the large rhyolite
complexes of Haroharo and Tarawera, with others at Mt Edgecumbe, Okareka
and Rotoma. During the last 22 000 years about 80 km2 of magma
has been erupted. On 10 June 1886 the most recent eruption formed the
1886 Tarawera Rift.
Okataina Area Seismicity
(125kb)
Waimangu Crater Lakes
Geodetic Observations
Taupo Fault Belt
The Taupo Fault Belt is a 70 km long northeast trending series of en echelon
grabens. It extends from the southern margin of the Rotorua-Okataina volcanic
centres to the northern margin of Taupo Volcanic Centre. The orientation
of the major normal faults forming this belt changes progressively along
its length. All historic fault breaks in the TVZ have occurred within
this fault belt. Vertical displacements range from less than 1 m to over
500 m.
Taupo Fault Belt Seismicity
(109kb)
Taupo Volcanic Centre
The Taupo Volcanic Centre consists of a large basin, about 50 km across
and 300-500 m deep. The central 600 km2 is occupied by Lake
Taupo. During the last 50 000 years at least 220 km3 of magma has been
erupted. The last major eruption occurred 1800 years ago.
Geodetic Observations
Taupo Area Seismicity (128kb)
Mt Egmont (Taranaki)
Egmont (Taranaki) Volcano in Taranaki began erupting some 130 000 years
ago. Since then there have been about eight substantial collapses of the
cone in which debris avalanches and lahars have spread widely over the
adjacent ring-plain. Each of these collapses has been followed by a period
of tephra and/or lava emission in which the structure has been rebuilt.
Mt Egmont is now a steep-sided cone rising to an altitude of 2518 m. The
summit is formed by a lava dome emplaced after the last major eruption,
about 360 years BP. Fantham's Peak (1962 m) is a parasitic cone on the
southern flank of Mt Egmont, which formed in a series of eruptions about
3100 years BP. Egmont volcano has been dormant since the last minor eruption
about 1755 AD.
Taranaki Area Seismicity
(110kb)
Tongariro Volcanic Centre
The Tongariro Volcanic Centre includes the multiple andesite massifs of
Tongariro and Ruapehu. The multiple strato-volcano Tongariro includes
the satellite cone of Ngauruhoe, which commenced erupting about 2500 years
ago. The last major eruption of Ngauruhoe was on 19 February 1975, when
strong explosive activity sent eruption columns to 10 km and pyroclastic
flows moved down the flanks.
Ruapehu is a complex composite andesite volcano built in at least four
cone-building episodes involving both central (summit) and flank events
during the last 260 000 years. The volcano rises to 2797 m and at present
has a single vent, now occupied by Crater Lake. Major phreatomagmatic
eruptions have occurred in 1969, 1971, 1975, 1995 and 1996.
Location Map
Tongariro Area Seismicity
(163kb)
Volcano-Seismic Activity
at Ruapehu (91kb)
Volcano-Seismic Activity
at Ngauruhoe and Tongariro (163kb)
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