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  • 1
    Electronic Resource
    Electronic Resource
    Palaeomagnetism and chronology of the central Taupo Volcanic Zone, New Zealand (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 124 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The central Taupo Volcanic Zone (TVZ) of New Zealand is a region of intense Quaternary silicic volcanism, active since 1.6 Ma. We report palaeomagnetic measurements from 59 distinct volcanic units sampled at 98 sites in the TVZ. These are mainly rhyolitic ignimbrites and lava domes, with a few basaltic, andesitic, and dacitic lavas. Most have new K/Ar or 40Ar/39 Ar ages. The remanent magnetizations are generally stable to both thermal and alternating-field demagnetization, and well-determined mean palaeodirections were obtained for all sites.Our findings suggest that the Taupo, Whakamaru, Maroa, Reporoa, Rotorua, and Okataina volcanic centres were magnetized during the Brunhes normal chron. Kapenga is an older volcanic centre, where activity commenced around 0.89 Ma and extended into the Brunhes. Mangakino volcanic centre is significantly older and was active from 1.6 to 0.95 Ma.Transitional or intermediate palaeodirections were obtained from Ahuroa ignimbrite (1.18 ± 0.02 Ma) and Mamaku ignimbrite (0.22 ± 0.01 Ma). The former almost certainly corresponds to the Cobb Mountain Event. The latter is significantly older than the Blake Event, and probably corresponds to the recently reported Pringle Falls/Summer Lake magnetic episode.Multiple sites from the Whakamaru ignimbrite have indistinguishable 40Ar/39 Ar ages (0.33 ± 0.01 Ma) and glass composition, but divergent palaeomagnetic directions. This contrast suggests that either (1) the different sites were formed during a phase of extremely violent activity, lasting up to a few hundred years, during which geomagnetic secular variation was recorded; or (2) that they were formed in a single eruption, and rotation during subsequent extensional tectonism has caused divergence of the palaeodirections. 40Ar/39Ar ages of 0.77 ± 0.03 Ma for the reversely magnetized Rahopeka ignimbrite and 0.71 ± 0.06 Ma for the overlying normally magnetized Waiotapu ignimbrite bracket and constrain the age of the Maluyama-Brunhes transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb05645.x
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  • 2
    Electronic Resource
    Electronic Resource
    Sedimentation and volcanism in a Permian arc-related basin, southern New Zealand (1989)
    Springer
    Bulletin of volcanology 51 (1989), S. 433-450 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract An exceptionally well-exposed, ancient, intra-arc basin in the Permian Takitimu Group of New Zealand contains 14 km of interbedded primary volcanic and marine volcaniclastic rocks of basaltic to rhyodacitic composition. These are the products of subaerial and submarine arc volcanism and closely associated turbidite sedimentation. The Takitimu oceanic arc/basin setting formed a dynamic closed sedimentary system in which large volumes of volcaniclastic material generated at the arc was rapidly redeposited in marine basins flanking the eruptive centres. Volcanism probably included (1) moderate- to deep-water extrusion of lava and deposition of hyaloclastite, (2) extrusive and explosive eruptions from shallow marine to marginally emergent volcanoes in or on the margin of the basin, and (3) Plinian and phreato-Plinian eruptions from more distant subaerial vents along the arc. Much of the newly erupted material was rapidly transported to the adjacent marine basin by debris flows, slumping and sliding. Hemipelagic sedimentation predominated on the outer margin of the basin, infrequently interrupted by deposition of ash from the most explosive arc volcanism and the arrival of extremely dilute turbidites. Turbidite sedimentation prevailed in the remainder of the basin, producing a thick prograding volcaniclastic apron adjacent to the arc. The volcaniclastic strata closely resemble classic turbidite deposits, and show similar lateral facies variations to submarine fan deposits. Study of such sequences provides insight into poorly understood processes in modern arc-related basins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01078810
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  • 3
    Electronic Resource
    Electronic Resource
    A vesicularity index for pyroclastic deposits (1989)
    Springer
    Bulletin of volcanology 51 (1989), S. 451-462 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The vesicularity of juvenile clasts in pyroclastic deposits gives information on the relative timing of vesiculation and fragmentation, and on the role of magmatic volatiles versus external water in driving explosive eruptions. The vesicularity index and range are defined as the arithmetic mean and total spread of vesicularity values, respectively. Clast densities are measured for the 16–32 mm size fraction by water immersion techniques and converted to vesicularities using measured dense-rock equivalent densities. The techniques used are applied to four case studies involving magmas of widely varying viscosities and discharge rates: Kilauea Iki 1959 (basalt), Eifel tuff rings (basanite), Mayor Island cone-forming deposits (peralkaline rhyolite) and Taupo 1800 B.P. (calc-alkaline rhyolite). Previous theoretical studies suggested that a spectrum of clast vesicularities should be seen, depending on the magma viscosity, eruption rate, and the presence and timing of magma: water interaction. The new data are consistent with these predictions. In magmatic “dry” eruptions the vesicularity index lies uniformly in the range 70%–80% regardless of magma viscosity. For high viscosities and eruption rates the vesicularity ranges are narrow (〈 25%), but broaden to between 30% and 50% as the viscosity and eruption rates are lowered and the volatiles and magma can de-couple. In phreatomagmatic “wet” eruptions, widely varying clast vesicularities reflect complex variations in the relative timing of vesiculation and water-induced fragmentation. Magma:water interaction at an early stage greatly reduces the vesicularity indices (〈 40%) and broadens the ranges (as high as 80%), whereas late-stage interaction has only a minor effect on the index and broadens the range to a limited extent. Clast vesicularity represents a useful third parameter in addition to dispersal and fragmentation to characterise pyroclastic deposits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01078811
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  • 4
    Electronic Resource
    Electronic Resource
    Rothenberg scoria cone, East Eifel: a complex Strombolian and phreatomagmatic volcano (1989)
    Springer
    Bulletin of volcanology 52 (1989), S. 28-48 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Rothenberg scoria cone Eifel formed by an alternation of three Strombolian and three phreatomagmatic eruptive phases. Eruptions took place from up to six vents on a 600 m-long fissure, building an early tuff ring and then two coalescing scoria cones. Strombolian volcanism dominated volumetrically, as the supply of external water was severely limited. Magma/water interaction only occurred during the opening stages of eruption at any vent, when discharge rates were low and the fragmentation surface was below the water table. The phreatomagmatic deposits consist of relatively well-sorted fall beds and only minor surge deposits. They contain juvenile clasts with a wide range of vesicularity and grain size, implying considerable heterogeneity in the assemblage of material ejected by the phreatomagmatic explosions. the transition from phreatomagmatic to Strombolian eruption at any vent was rapid and irreversible, and Strombolian volcanism persisted even when eruption rates are inferred to have waned at the close of each eruptive phase as, by then, the fragmentation surfaces were high in the growing cones and water was denied access to the magma. The Strombolian deposits are relatively homogenous, consisting of alternating coarser- and finer-grained, well-sorted fall beds erupted during periods of open-vent eruption and partial blockage of the vent respectively. The intervals of Strombolian eruption were always a delicate balance between discharge of freely degassing magma and processes such as ponding of degassed magma in the vent, collapse of the growing cones, and repeated recycling of clasts through the vent. Clear evidence of the instability of the Rothenberg cones is preserved in numerous unconformities within deposits of the inner walls of the cones. The close of Strombolian phases was probably marked by a decreasing supply of magma to the vents accompanied by ponding and stagnation of lava in the craters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00641385
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  • 5
    Electronic Resource
    Electronic Resource
    Vent migration and changing eruptive style during the 1800a Taupo eruption: new evidence from the Hatepe and Rotongaio phreatoplinian ashes (1995)
    Springer
    Bulletin of volcanology 57 (1995), S. 432-439 
    Details
    ISSN: 1432-0819
    Keywords: Key words Taupo eruption ; Plinian ; Phreatoplinian ; Vent migration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The 1800a Taupo eruption was one of the most complex silicic eruptions worldwide within the past 5000 years. New work on phases 3 and 4, the Hatepe and Rotongaio ashes, has identified a mappable internal stratigraphy for each, enabling detailed isopach and isopleth measurements for subunits within the deposits. The new data indicate that the vent configuration for the Taupo eruption was more complex than previously thought and involved at least three sources on a NE–SW fissure centred on Horomatangi Reefs. Phases 1–3 of the eruption were from a southwestern vent(s), phase 4 from a northeastern source, and phases 5 and 6 probably from the Horomatangi Reefs area. A separate source for the Rotongaio ash (phase 4) helps explain the contrast between the pumice-rich phases of the eruption and the dense juvenile clasts of the Rotongaio ash. The Rotongaio magma resided in a separate, initially blind conduit and was degassing prior to and during earlier phases of the Taupo eruption. This new work on the Hatepe and Rotongaio ashes underscores the importance of a detailed stratigraphic framework in deciphering extremely fine-grained fall units of large-scale sustained eruptions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00300987
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  • 6
    Electronic Resource
    Electronic Resource
    Mixed deposits of complex magmatic and phreatomagmatic volcanism: an example from Crater Hill, Auckland, New Zealand (1996)
    Springer
    Bulletin of volcanology 58 (1996), S. 59-66 
    Details
    ISSN: 1432-0819
    Keywords: Key words Explosive volcanism ; Magmatic ; Phreatomagmatic ; Crater Hill ; Basalt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  A series of alternating phreatomagmatic ("wet") and magmatic ("dry") basaltic pyroclastic deposits forming the Crater Hill tuff ring in New Zealand contains one unit (M1) which can only be interpreted as the products of mixing of ejecta from simultaneous wet and dry explosions at different portions of a multiple vent system. The principal characteristics of M1 are (a) rapid lateral changes in the thicknesses of, and proportions in juvenile components in individual beds, and (b) wide ranges of juvenile clast densities in every sample. M1 appears to have been associated with an elongate source of highly variable and fluctuating magma : water ratios and magma discharge rates. This contrasts with the only other documented mixed (wet and dry) basaltic pyroclastic deposits where mixing from two point sources of quite different but stable character has been inferred.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450050126
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  • 7
    Electronic Resource
    Electronic Resource
    Tephra, snow and water: complex sedimentary responses at an active snow-capped stratovolcano, Ruapehu, New Zealand (2000)
    Springer
    Bulletin of volcanology 62 (2000), S. 278-293 
    Details
    ISSN: 1432-0819
    Keywords: Stratovolcano Explosive volcanism Tephra remobilisation Lahars Ruapehu Volcanic hazards
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract. A feature of small-scale explosive volcanism at stratovolcanoes is the rapid destruction of primary near-vent pyroclastic deposits by sedimentary processes. A protracted series of explosive eruptions of moderate volume from September 1995 until July 1996 at Mount Ruapehu in New Zealand, its largest eruptive episode this century, afforded an opportunity to study these remobilisation processes in detail. All significant sub-plinian eruptions occurred in mid-winter, forming metre-thick tephra accumulations on steep slopes covered with perennial ice and seasonal snow. Subsequent events demonstrated the variety and complexity of the erosion processes that remobilise primary pyroclasts in such a setting. These processes arose from the complex interactions of tephra with snow and ice, and liquid water in varying proportions, and were very diverse in nature and scale. Their effectiveness can be gauged from the fact that there is almost no stratigraphic record of any of the 〉40 eruption episodes recorded in the past 100 years at Ruapehu. Syn-eruptive remobilisation processes included the generation of eruption-triggered lahars by the ejection of hot water from the Crater Lake. Post-eruptive interactions mainly remobilised fall deposits from proximal areas, and included rain-triggered lahars, which were among the largest and most hazardous events with the greatest distal impacts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004450000096
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  • 8
    Electronic Resource
    Electronic Resource
    A facies model for a quaternary andesitic composite volcano: Ruapehu, New Zealand (1989)
    Springer
    Bulletin of volcanology 51 (1989), S. 51-68 
    Details
    ISSN: 1432-0819
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Ruapehu composite volcano is a dynamic volcanic-sedimentary system, characterised by high accumulation rates and by rapid lateral and vertical change in facies. Four major cone-building episodes have occurred over 250 Ka, from a variety of summit, flank and satellite vents. Eruptive styles include subplinian, strombolian, phreatomagmatic, vulcanian and dome-related explosive eruptions, and extrusion of lava flows and domes. The volcano can be divided into two parts: a composite cone of volume 110 km3, surrounded by an equally voluminous ring plain. Complementary portions of Ruapehu's history are preserved in cone-forming and ring plain environments. Cone-forming sequences are dominated by sheet- and autobrecciated-lava flows, which seldom reach the ring plain. The ring plain is built predominantly from the products of explosive volcanism, both the distal primary pyroclastic deposits and the reworked material eroded from the cone. Much of the material entering the ring plain is transported by lahars either generated directly by eruptions or triggered by the high intensity rain storms which characterise the region. Ring plain detritus is reworked rapidly by concentrated and hyperconcentrated streams in pulses of rapid aggradation immediately following eruptions and more gradually in the longer intervals between eruptions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01086761
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  • 9
    Electronic Resource
    Electronic Resource
    An exceptionally widespread ignimbrite with implications for pyroclastic flow emplacement (1995)
    [s.l.] : Nature Publishing Group
    Nature 378 (1995), S. 605-607 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The central Taupo Volcanic Zone (TVZ; Fig. 1) is the most productive Quaternary rhyolitic volcanic system on Earth. At least 34 voluminous ignimbrites (30-1,000 km3 bulk volume) have been erupted from eight caldera volcanoes"'12 in central TVZ since 1.6Myr. Several of the New Zealand ignimbrites ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/378605a0
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  • 10
    Electronic Resource
    Electronic Resource
    Vent migration and changing eruptive style during the 1800a Taupo eruption: new evidence from the Hatepe and Rotongaio phreatoplinian ashes (1995)
    Springer
    Bulletin of volcanology 57 (1995), S. 432-439 
    Details
    ISSN: 1432-0819
    Keywords: Taupo eruption ; Plinian ; Phreatoplinian ; Vent migration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The 1800a Taupo eruption was one of the most complex silicic eruptions worldwide within the past 5000 years. New work on phases 3 and 4, the Hatepe and Rotongaio ashes, has identified a mappable internal stratigraphy for each, enabling detailed isopach and isopleth measurements for subunits within the deposits. The new data indicate that the vent configuration for the Taupo eruption was more complex than previously thought and involved at least three sources on a NE-SW fissure centred on Horomatangi Reefs. Phases 1–3 of the eruption were from a southwestern vent(s), phase 4 from a northeastern source, and phases 5 and 6 probably from the Horomatangi Reefs area. A separate source for the Rotongaio ash (phase 4) helps explain the contrast between the pumice-rich phases of the eruption and the dense juvenile clasts of the Rotongaio ash. The Rotongaio magma resided in a separate, initially blind conduit and was degassing prior to and during earlier phases of the Taupo eruption. This new work on the Hatepe and Rotongaio ashes underscores the importance of a detailed stratigraphic framework in deciphering extremely fine-grained fall units of largescale sustained eruptions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00300987
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    Paper (German National Licenses)
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