In: Decker RW, Wright TL, Stauffer PH (eds) Volcanism in Hawaii. Unpublished PhD thesis lodged in the Library, Victoria University of Wellingtonįournier RO (1987) Conceptual models of brine evolution in magmatic-hydrothermal systems. International Association of Volcanology and Chemistry of the Earth's Interior, Naplesĭuncan AR (1970) Eastern Bay of Plenty volcanoes. NZ Geol Surv Bull 103:69–84Ĭole JW, Nairn IA (1975) Catalogue of the active volcanoes of the world including Solfatara fields. NZ Geol Surv Bull 103:109–118Ĭlark RH, Otway PM (1989) Deformation monitoring associated with the 1976–82 White Island eruption sequence. J Geol Soc Lond 132:429–440Ĭhristoffel DA (1989) Variations in magnetic field intensity at White Island volcano related to the 1976–82 eruption sequence. Bull Volcanol 34:158–167īlackburn EA, Wilson L, Sparks RSJ (1976) Mechanisms and dynamics of strombolian activity. When the walls were unstable, wall collapse triggered larger discrete phreatomagmatic explosions.īlack PM (1970) Observations on White Island Volcano, New Zealand. If the walls were relatively stable, fine ash was slowly eroded and erupted in weak, near-continous phreatomagmatic events.
The form of these ‘wet’ explosions was governed by a delicate balance between erosion and collapse of the weak conduit walls. While true Strombolian phases did occur, more frequently the decoupled magmatic gas rose to interact with the conduit walls and hydrothermal system, producing phreatomagmatic eruptions. The low rate of magma rise led to very effective separation of magmatic volatiles and high fluxes of magmatic gas even during phreatic phases of the eruption. This White Island eruption was unusual because of the low discharge rate of magma over an extended time period and because of the influence of a unique physical and hydrological setting. The key features of the larger explosions were their shallow focus, random occurrence and lack of precursors, and the thermal heterogeneity of the ejecta. The larger discrete explosions produced ballistic block aprons, downwind lobes of fall tephra, and cohesive ‘wet’ surge deposits confined to the main crater. The near-continuous activity reculted from streaming of magmatic volatiles and phreatic steam through open conduits, frittering juvennile shards from the margins of the magma and eroding loose lithic particles from the unconsolidated wall rock.
Phreatomagmatic phases contained two styles of activity: (a) near-continuous emission of gas and ash and (b) discrete explosions followed by prolonged quiescence. Strombolian eruptions were preceded and followed by mildly explosive degassing and production of incandescent, blocky juvenile ash from the margins of the magma body. The eruption sequence consisted of seven alternating phases of phreatomagmatic and Strombolian volcanism. Vent position within the craters changed 5 times during the eruption, but the vents were repeatedly re-established along a line linking pre-1976 vents. About 10 7 m 3 of mixed lithic and juvenile ejecta was erupted, accompanied by collapse to form two coalescing maar-like craters. The rise of at least 10 6 m 3 of basic andesite magma to shallow levels and its interaction with the hydrothermal system resulted in the longest historical eruption sequence at White Island in 1976–1982.
White Island is an active andesitic-dacitic composite volcano surrounded by sea, yet isolated from sea water by chemically sealed zones that confine a long-lived acidic hydrothermal system, within a thick sequence of fine-grained volcaniclastic sediment and ash.