Sumisu volcano, Izu-Bonin arc, Japan: site of a silicic caldera-forming eruption from a small open-ocean island

Abstract

Sumisu volcano was the site of an eruption during 30-60 ka that introduced ∼48-50 km 3 of rhyolite tephra into the open-ocean environment at the front of the Izu-Bonin arc. The resulting caldera is 8 × 10 km in diameter, has steep inner walls 550-780 m high, and a floor averaging 900 m below sea level. In the course of five research cruises to the Sumisu area, a manned submersible, two ROVs, a Deep-Tow camera sled, and dredge samples were used to study the caldera and surrounding areas. These studies were augmented by newly acquired single-channel seismic profiles and multi-beam seafloor swath-mapping. Caldera-wall traverses show that pre-caldera eruptions built a complex of overlapping dacitic and basaltic edifices, that eventually grew above sea level to form an island about 200 m high. The caldera-forming eruption began on the island and probably produced a large eruption column. We interpret that prodigious rates of tephra fallback overwhelmed the Sumisu area, forming huge rafts of floating pumice, choking the nearby water column with hyperconcentrations of slowly settling tephra, and generating pyroclastic gravity currents of water-saturated pumice that traveled downslope along the sea floor. Thick, compositionally similar pumice deposits encountered in ODP Leg 126 cores 70 km to the south could have been deposited by these gravity currents. The caldera-rim, presently at ocean depths of 100-400 m, is mantled by an extensive layer of coarse dense lithic clasts, but syn-caldera pumice deposits are only thin and locally preserved. The paucity of syncaldera pumice could be due to the combined effects of proximal non-deposition and later erosion by strong ocean currents. Post-caldera edifice instability resulted in the collapse of a 15°sector of the eastern caldera rim and the formation of bathymetrically conspicuous wavy slump structures that disturb much of the volcano's surface.

Volcanic evolution of the South Sandwich volcanic arc, South Atlantic, from multibeam bathymetry

“…Caldera diameters range from 1.6 to 6 km, within the somewhat larger range of caldera diameters recorded in the Tonga-Kermadec (Wright et al, 2006;Massoth et al, 2007;I.J. Graham et al, 2008) and Izu-Bonin (Yuasa et al, 1991;Fiske et al, 2001;Tani et al, 2008) intraoceanic arcs. Floors of the submarine calderas are imaged as nearly flat, with local mounds that may represent lavas or large hydrothermal mounds.…”

“…It is therefore possible that there is a general association between silicic products and caldera collapse in the South Sandwich arc as well documented in the Tonga-Kermadec (Worthington et al, 1999;Smith et al, 2003;Wright et al, 2006; I.J. Barker et al, 2012), Izu-Bonin (Fiske et al, 2001;Tani et al, 2008) and Vanuatu (Robin et al, 1993;Monzier et al, 1994) intra-oceanic arcs. Historic volcanic or hydrothermal activity has been observed at most of the South Sandwich calderas (Table 2).…”

Structural characteristics of the Bayonnaise Knoll caldera as revealed by a high-resolution seismic reflection survey

“…Velocity structure variations of both calderas are very similar. The Myojin Knoll caldera is estimated to have similar lithologies along the Sumisu rift, as indicated by geophysical and geological observations (Fiske et al 2001;Tani et al 2008;Tsuru et al 2008). This suggests that the Bayonnaise Knoll caldera and Myojin Knoll caldera also have similar lithologies, which are mainly composed of pumiceous sand and gravels; the data suggestive of this were revealed at the eastern margin of the Sumisu rift in the Izu-Ogasawara back-arc, i.e., Ocean Drilling Program (ODP) site 788 of Leg 126 (Taylor 1992).…”

“…The Bayonnaise Knoll caldera walls are mainly composed of thick volcanic breccia, as estimated from data similar to the comparisons between the velocity structure (Tsuru et al 2008) and geological sampling data (Naka et al 1995) in the Myojin Knoll caldera. In the case of the Sumisu caldera, there are symmetric characteristics along the north-south profile and asymmetric characteristics along the east-west profile that were discovered by a single-channel seismic survey (Tani et al 2008). Regarding the structural symmetry of the caldera, it presents different characteristics that include uncertainties of the effect of the direction for volcanic arrangement.…”

“…According to the drilling results (Nishimura et al 1991(Nishimura et al , 1992, there are pumiceous deposits with a thickness of more than 250 m from 0.2 Ma to present. Tani et al (2008) suggested that the source of these pumiceous deposits was produced in the Sumisu volcano. Tanahashi et al (2006) recognized many tuffaceous volcanic breccia in and around the Bayonnaise Knoll caldera via seafloor camera observations.…”