Eruption mechanisms during the climax of the Tarawera 1886 basaltic Plinian eruption inferred from microtextural characteristics of the deposits
Published:January 01, 2009
J. E. Sable, B. F. Houghton, C. J. N. Wilson, R. J. Carey, 2009. "Eruption mechanisms during the climax of the Tarawera 1886 basaltic Plinian eruption inferred from microtextural characteristics of the deposits", Studies in Volcanology: The Legacy of George Walker, T. Thordarson, S. Self, G. Larsen, S. K. Rowland, Á. Höskuldsson
Download citation file:
During the climactic Plinian phase of the 1886 basaltic eruption of Tarawera, New Zealand, vents along the 17 km fissure erupted explosively with a wide range of dispersal. The 8 km long segment of the fissure which cuts across Mt Tarawera contains approximately 50 vents and includes the sources of both the weakest and most intense activity of the 5 h eruption. We seek to explain (1) what allowed the intensity to reach Plinian values that are rarely achieved by basaltic magma, and (2) what caused adjacent vents to erupt with very different dispersals and intensities despite identical magma composition. All juvenile clasts studied from this eruption have relatively high vesicle number densities (c. 106cm-3) and exceptionally high microlite crystallinities (60–90% of the groundmass), unlike the typical products of weaker Hawaiian and Strombolian basaltic explosions. Textural analysis of juvenile pyroclasts suggests that all the erupted magma experienced the same decompression history through to fragmentation. The Tarawera magma experienced a sudden, large, decompression producing nucleation of bubbles and microlites. The high microlite content was the primary means by which the magma’s viscosity increased, which kept the bubble population well coupled to the magma and allowed it to fragment explosively in a manner analogous to that postulated for silicic Plinian eruptions. The main differences at different sites along the Mt Tarawera fissure segment are in the amount and grain size of the wall rock lithic component of the deposits. We suggest that conduit/vent erosion and incorporation of significant volumes of cold wall rock into theeruptive jet prevented some vents from achieving Plinian intensity. Bubble size analysis suggests that coalescence ledto open-system degassing, ending the Plinian phase.
Figures & Tables
Studies in Volcanology: The Legacy of George Walker
Professor George Patrick Leonard Walker was one of the fathers of modern quantitative volcanology and arguably the foremost volcanologist of the twentieth century. In his long career, George studied a wide spectrum of volcanological problems and in doing so influenced almost every branch of the field. This volume, which honours his memory and his contributions to the field of volcanology, contains a collection of papers inspired by, and building upon, many of the ideas previously developed by George. Many of the contributors either directly studied under and worked with George, or were profoundly influenced by his ideas. The topics broadly fall under the three themes of lava flows and effusion, explosive volcanism, and volcanoes and their infrastructure.