Formation of scoria cone during explosive eruption at Izu‐Oshima volcano, Japan

Abstract

[1] Scoria cones have been regarded to be formed by accumulation of ballistic bombs ejected by mild eruptions. However, more recent geological investigations show that some scoria cones could be formed during explosive eruptions. Here, we demonstrate how the scoria cone of the 1986 Izu-Oshima eruption was formed during the explosive eruption. We measured particle fractionation of the cone and propose a theoretical model to explain the observation. The model considers lateral transport of particles by turbulent eddies; particles that reached characteristic column radius, L, are laterally transported to wL where they starts to free-fall. We obtained w = 1.2 and 2.5 for larger and smaller particles, respectively, which is consistent to the observation. In the model, extensive fallout takes place at the base of the column where it expands rapidly. We suggest that lateral particle projection and the rapid column expansion are the key processes to form the cones.

Monogenetic Basaltic Volcanoes: Genetic Classification, Growth, Geomorphology and Degradation

“…This proposed behaviour is similar to the proximal sedimentation from convective plumes, forming cones with similar geometry to scoria cones, e.g. the 1886 eruption of Tarawera, Taupo Volcanic Zone, New Zealand [375] or the 1986 eruption of Izu-Oshima volcano, Japan [368]. The fines content does not fulfil the criteria of pure ballistic trajectory, thus turbulent, momentum-driven eruption jets ( Figure 9A) should be part of the cone growth mechanisms [182,368,376].…”

“…the 1886 eruption of Tarawera, Taupo Volcanic Zone, New Zealand [375] or the 1986 eruption of Izu-Oshima volcano, Japan [368]. The fines content does not fulfil the criteria of pure ballistic trajectory, thus turbulent, momentum-driven eruption jets ( Figure 9A) should be part of the cone growth mechanisms [182,368,376]. As documented above, scoria cones demonstrate a wider range of granulometric characteristics [182] than previously thought [185].…”

“…However, recent studies found that the typical exit velocities are about 100-120 m/s [180,183] and they could reach as high as 400 m/s [373]. These studies also showed that the typical particle diameter is cm-scale or less instead of dm-scale [180,183], which cannot be derived purely from impact breakage of clasts upon landing [182,368]. Especially during paroxysmal activity at Stromboli [374] or more energetic violent Strombolian activity [83,163], the dominance of fine particles in the depositional records contradicts the ballistics emplacement model for the cones.…”

“…On a fresh edifice, where no post-eruptive surface modification has taken place, these morphometric parameters are related to the primary attributes of eruption dynamics and syn-eruptive sedimentary processes. However, there are potentially two valid models to explain their dominant construction mechanisms, including a ballistic emplacement with drag forces and fallout from turbulent, momentum-driven jets at the gas-thrust region [84,182,185,[368][369]. In both models, the angle of repose requires loose, dry media.…”

Environmental Effects of Volcanic Volatile Fluxes From Subaerial Large Igneous Provinces

“…Eruptions from Hawaii in the early 1980s generated fire-fountains with heights up to 500 m generating buoyant plumes up to 11 km ASL (7.5 km above the vent) (Self et al, 2015). At the basaltic fissure eruption of Izu-Oshima volcano in Japan, lava fountains 1.6 km high were observed to feed an ashy sub-Plinian plume that reached 16 km altitude (Endo et al, 1988;Mannen & Ito, 2007). Modeling studies have captured many of these observations and suggest that near-stratospheric heights could be attained by high-intensity basaltic eruptions (Stothers et al, 1986;Woods, 1993;Kaminski et al, 2011;Glaze et al, 2011Glaze et al, , 2017.…”