Silicic lava dome growth in the 1934–1935 Showa Iwo-jima eruption, Kikai caldera, south of Kyushu, Japan

Abstract

The 1934The -1935 Showa Iwo-jima eruption started with a silicic lava extrusion onto the floor of the submarine Kikai caldera and ceased with the emergence of a lava dome. The central part of the emergent dome consists of lower microcrystalline rhyolite, grading upward into finely vesicular lava, overlain by coarsely vesicular lava with pumice breccia at the top. The lava surface is folded, and folds become tighter toward the marginal part of the dome. The dome margin is characterized by two zones: a fracture zone and a breccia zone. The fracture zone is composed of alternating layers of massive lava and welded oxidized breccia. The breccia zone is the outermost part of the dome, and consists of glassy breccia interpreted to be hyaloclastite. The lava dome contains lava with two slightly different chemical compositions; the marginal part being more dacitic and the central part more rhyolitic. The fold geometry and chemical compositions indicate that the marginal dacite had a slightly higher temperature, lower viscosity, and lower yield stress than the central rhyolite. The high-temperature dacite lava began to effuse in the earlier stage from the central crater. The front of the dome came in contact with seawater and formed hyaloclastite. During the later stage, low-temperature rhyolite lava effused subaerially. As lava was injected into the growing dome, the fracture zone was produced by successive fracturing, ramping, and brecciation of the moving dome front. In the marginal part, hyaloclastite was ramped above the sea surface by progressive increments of the new lava. The central part was folded, forming pumice breccia and wrinkles.

Non-explosive magma–water interaction in a continental setting: Miocene examples from the Eastern Cordillera (central Andes; NW Argentina)

“…7) can be interpreted as hyaloclastite intraclasts. Similar shape, textural, and petrographic characteristics were partly described in subaqueous lava domes (Cas et al 1990;De Rita et al 2001;Goto and Tsuchiya 2004), and at the margin of subaerial domes that came in contact with water (Kokelaar 1986;Maeno and Taniguchi 2006). In the case of the stratified matrix-rich polymictic volcanic breccia, we interpret the juvenile components to be derived from a lava dome(s), the marginal parts of which interacted with surface water.…”

“…Patino et al 2003), but concentric arrangement of textures is also described in pillow lavas (e.g. Walker 1992), at the marginal parts of lava domes (Maeno and Taniguchi, 2006), and in intrusive pillows (Yamagishi 1987;.…”

“…During magma extrusion, the marginal parts of the dome(s) came in contact with water ( Fig. 15a), where hot lava was rapidly cooled, fractured, and fragmented, and hyaloclastite was generated by brittle spalling (Maeno and Taniguchi 2006). Gravitational collapses produced the syn-eruptive resedimentation of the marginal part of the dome(s) and the deposition of the stratified matrix-rich polymictic volcanic breccia (Figs.…”

“…The clast types are referable to the typical outward textural zonation recorded in subaerial lavas and lava domes (Huppert et al 1982;McPhie et al 1993;Maeno and Taniguchi 2006), which comprises, from the lava or dome core: (i) Coherent porphyritic massive lava with crystalline groundmass; (ii) coherent flow-banded lava; (iii) finely vesicular coherent glassy lava; (iv) coarsely vesicular coherent glassy lava; and (v) glassy, pumiceous autoclastic breccia. The monomictic amphibole-phyric andesite breccia facies is a poorly sorted, massive mixture of dense juvenile blocks (decimetre-to metre-sized) within a lapilli-sized matrix that contains little fine ash (Fig.…”

Automated identification of lava flow structures using local Fourier spectrum of digital elevation data

“…The range of viscosities estimated for the flow crust and interior compares favorably with the estimates of viscosities for other elongate dacite flows. Friedman et al [1963] estimated a surface viscosity for the 1953 Trident dacite flow of h o = 6.9 Â 10 10 PaÁs using flow velocity and geometry; Fink [1980a] estimated that the Chao dacite flow, Chile had viscosities of h o = 1.5 Â 10 11 PaÁs and h i = 4.6 Â 10 9 PaÁs using fold geometry; Maeno and Taniguchi [2006] estimated that high-silica dacite portion of the Showa Iwojima flow, Japan had viscosities of h o = 10 11 PaÁs and h i = 10 7 -10 8 PaÁs also using fold geometry.…”