The 1976-82 eruption sequence at White Island volcano (Whakaari), Bay of Plenty, New Zealand

(Inc. GST)
(Ex. GST)
Write a Review

Houghton, B.F.; Nairn, I.A. 1989 The 1976-82 eruption sequence at White Island volcano (Whakaari), Bay of Plenty, New Zealand. Lower Hutt: New Zealand Geological Survey. New Zealand Geological Survey bulletin 103 138 p.

Abstract: The 1976-82 activity of White Island was the largest and longest eruption sequence of the last 100 years, and ejected juvenile basic andesite blocks and bombs not previously recorded from the island. The 1976-82 eruption sequence appears to have been the result of rise of a basic andesite magma body beneath White Island crater, reaching its highest levels in mid-1977, when eruptive activity, measured crater uplift, and the negative magnetic anomaly all peaked. All recent White Island activity has occurred in the western subcrater, a deep prehistoric basin, which extends below sea level. Prior to 1976, the basin was infilled with reworked and altered pyroclastics and sediments, and saturated with hot groundwater acidified by dissolved volcanic gases. The rising magma interacted with this crater-fill material. Parts of the wet crater fill were remobilised by physical processes induced by the magmatic intrusion, and were entrained in the venting steam and gas plumes of the initial eruptions. These eruptions excavated voids above the rising magma body, into which overlying fill material was engulfed to form large vertical-walled collapse craters or maars. The formation of these collapse craters was the most spectacular morphological change to have occurred at White Island since the 1914 crater wall collapse and debris avalanche. The eruption proceeded through cycles of initial vent-clearing phreatomagmatic activity which ejected crater-fill material, followed by strombolian eruptions when the magma column was exposed to the atmosphere in an open vent. It ended when collapse of the vent and conduit walls re-established closed vent conditions. A brief microearthquake survey in 1986 found that low frequency volcanic earthquakes were located within a few hundred metres horizontally from the vent area, suggesting that magma/water interaction was occurring in a zone of dikes extending to a few kilometres depth. This seismic data has been combined with the deformation, magnetic, petrological and chemistry results to produce an integrated model of White Island activity and structure. (auths./KN)