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The cataclysmic basaltic eruption of Mt. Tarawera in 1886 represents a significant cultural and scientific event for New Zealand. This review utilises published and new observations, to reinterpret eruptive parameters encompassing the entirety of the eruption. The ∼17 km eruptive fissure, active for 4+ hours, extends across Mt. Tarawera to the hydrothermally active Waimangu region. Correlating published observations of bed thickness, componentry and microtextures from Mt. Tarawera to new bed descriptions and granulometry for the Rotomahana-Waimangu rift segment allows for a re-assessment of eruption variations along the length of the fissure. Variably thick pyroclastic fall sequences at Mt. Tarawera contrast with the pyroclastic surges and an eruption plume that together deposited the 'Rotomahana Mud' erupted along the Rotomahana-Waimangu segment. Providing insight into pre-eruptive conditions, new mineral chemistry from Mt. Tarawera provides the first constraints on crystallisation pressures (

The 7–8 August 2008 eruption of Kasatochi Island volcano blanketed the island in newly generated pyroclastic deposits and deposited ash into the ocean and onto nearby islands. Concentrations of water soluble Fe, Cu, and Zn determined from a 1:20 deionized water leachate of the ash were sufficient to provide short-term fertilization of the surface ocean. The 2008 pyroclastic deposits were thicker in concavities at bases of steeper slopes and thinner on steep slopes and ridge crests. By summer 2009, secondary erosion had exposed the pre-eruption soils along gulley walls and in gully bottoms on the southern and eastern slopes, respectively. Topographic and microtopographic position altered the depositional patterns of the pyroclastic flows and resulted in pre-eruption soils being buried by as little as 1 m of ash. The different erosion patterns gave rise to three surfaces on which future ecosystems will likely develop: largely pre-eruptive soils; fresh pyroclastic deposits influenced by shallowly bu...

Kasatochi Island, the subaerial portion of a small volcano in the western Aleutian volcanic arc, erupted on 7–8 August 2008. Pyroclastic flows and surges swept the island repeatedly and buried most of it and the near-shore zone in decimeters to tens of meters of deposits. Several key seabird rookeries in taluses were rendered useless. The eruption lasted for about 24 hours and included two initial explosive pulses and pauses over a 6-hr period that produced ash-poor eruption clouds, a 10-hr period of continuous ash-rich emissions initiated by an explosive pulse and punctuated by two others, and a final 8-hr period of waning ash emissions. The deposits of the eruption include a basal muddy tephra that probably reflects initial eruptions through the shallow crater lake, a sequence of pumiceous and lithic-rich pyroclastic deposits produced by flow, surge, and fall processes during a period of energetic explosive eruption, and a fine-grained upper mantle of pyroclastic-fall and -surge deposits that p...

The 21.9 ka Okareka and 17.6 ka Rerewhakaaitu rhyolite eruption episodes began the construction of Tarawera Volcano in the Okataina Volcanic Centre, Taupo Volcanic Zone. Examination of the proximal and medial stratigraphy of these moderate‐size (c. 5 km3 magma) but poorly exposed pyroclastic deposits has increased understanding of their eruption and dispersal processes. The Okareka Tephra consists of at least nine units (A‐I), with unit A basaltic scoria at the base, overlain by the rhyolitic units B‐I. Unit C is the largest individual plinian fall deposit (c. 0.4 km3), dispersed from an eruption column that reached c. 19 km height in the presence of strong crosswinds. The other pyroclastic units record a variety of phreatomagmatic, sub‐plinian, and small ignimbrite eruptions, which were followed by extrusion of voluminous lava flows. The Rerewhakaaitu Tephra consists of 15 rhyolitic fall units A‐N. An initial short plinian phase dispersed lapillifall unit A, mostly to ENE, from columns c. 15 km ...

The c. 5600 cal. yrBP Whakatane eruption episode consisted of a sequence of intracaldera rhyolite eruptions from at least five vents spread over 11 km of the Haroharo linear vent zone within Okataina Volcanic Centre. Initial vent‐opening eruptions from the Haroharo vent produced coarse lithic clast “blast beds” and pyroclastic density currents (surges). These were immediately followed by eruption of very mobile pumiceous pyroclastic surges from the Makatiti vent 6 km to the southwest. Major plinian eruptions from the Makatiti vent then dispersed Whakatane Tephra pumice fall deposits (bulk volume c. 6 km3) across the northeastern North Island while smaller explosive eruptions produced pyroclastic flows and falls from the Haroharo‐Rotokohu vents and at the Pararoa vent on the caldera rim 11 km northeast from Makatiti. The pyroclastic eruptions at all vents were followed by the extrusion of lava flows and domes; extruded lava volumes ranged from 0.03 km3 for the Pararoa dome to 7.5 km3 for the Makat...

Rotorua Ash is a widespread (>10 000km2) pyroclastic fall deposit erupted during extrusion of a rhyolite lava complex sited adjacent to the Lake Tikitapu basin, 10 km south-east of Rotorua City, North Island, New Zealand. The eruption was plinian in character, with maximum rate of emission occurring early in the eruption sequence to produce a high (c. 20 km) eruption column. Later explosions accompanied extrusion of lavas. Local, near-vent, pyroclastic flow and surge deposits may have resulted from periods of column collapse. Extrusion of a lava flow from the main pyroclastic vent appears to have terminated the eruption. A 14C age of 13 800 ± 250 years B.P. (new T 1/2) has been obtained for Rotorua Ash close to the source.

The emergent summit of Mayor Island, Bay of Plenty, New Zealand, is a peralkaline rhyolite volcano constructed by: a sequence of lava flows, the Tutaretare Rhyolite Formation (new); and pyroclastic deposits, the Oira Pyroclastite Formation (new). These 2 formations constitute the Mayor Island Group (new). The pyroclastic deposits mantle most of the outer slopes of the island, in places exceeding 100 m in thickness, and also occur interbedded with lava flows of the main cone. The pyroclastics have been informally assigned on the basis of their compositional, welding and textural, and sedimentary structural characteristics to one or other of 15 lithotypes which may be related to palrticular modes of eruption and emplacement, of both airfall (phreatic, phreatomagmatic, phreatoplinian, and plinian types) and pyroclastic flow (ignimbrite, nuee ardente, and base surge types) origins. A sixteenth lithotype comprises epiclastic deposits formed possibly by catastrophic overspill from an ancestral crater l...

Pyroclastic flow is defined as the flow of high-temperature, essential, fragmental materials. This is synonymous with the nuee ardente in the broad sense. Three modes of emplacement of high-temperature, essential, solid (or liquid) materials after the ejection from the crater may be recognized: 1) Projection of fragments from the crater by explosive expansion of gas within the crater; 2) descent of fragments or liquid magma from the crater caused only by the action of gravity; and 3) swift downflow of the mixture of gas and fragments. This last is intermediate between the first two and corresponds to pyroclastic flow. A new classification of pyroclastic flows is proposed based upon viscosity of the materials, which ls inferred from the nature of the deposit. The volume of the deposit increases as the viscosity decreases. 1) Nuee ardente in the strict sense: Represented by the nuee ardente of Mt. Pelee, Merapi, etc. The fragments are less porous, which indicates the high viscosity. The volume of the deposi...