The 1989 submarine eruption off eastern Izu Peninsula,Japan: ejecta and eruption mechanisms

The submarine eruption of a new small knoll, which was named Teishi knoll, off eastern Izu Peninsula behind the Izu-Mariana arc occurred in the evening of 13 July 1989. This is the first historic eruption of the Higashi-Izu monogenetic volcano group. The eruption of 13 July followed an earthquake swarm near Ito city starting on 30 June. There were subsequent volcanic tremors on 11 and 12 July, and the formation of the Teishi knoll on the 100 m deep insular shelf 4 km northeast of Ito city. There were five submarine explosions, which were characterized by intermittent domelike bulges of water and black tephra-jets, which occurred within 10 min on 13 July. Ejecta of the eruption was small in volume and composed of highly crystalline basalt scoria, highly vesiculated pumice, and lithic material. Petrographical features suggest that the pumice was produced by vesiculation of reheated wet felsic tuff of an older formation. The Teishi knoll, before the eruption, was a circular dome, 450 m across and 25 m high, with steep sides and a flat summit. Considerations of submarine topographic change indicate the knoll was raised by sill-like intrusion of 10⁶ m³ of magma beneath a 30 m thick sediment blanket. This shallow intrusion is assumed to have started on 11 July when volcanic tremors were observed for the first time, but there was no indications of violent interaction between wet host sediments and intruding magma. The submarine eruption of 13 July appears to have been Friggered by a major lowering of the magma-column. The basalt scoria, having crystal-contents of more than 60%, is assumed to be derived from the cooled plastic margin of the shallow intrusive body. However, glassy scoria, which would indicate the interaction between hot fluidal magma and external water, was not observed. A scenario for the 1989 submarine eruption is as follows. When rapid subsidence of the hot interior of the intrusive magma occurred, reduced pressure caused the implosion of cooled plastic magma, adjacent pressurized, hot host material, and wet sediment. The mixing of these materials triggered the vigorous vapor explosions.     

Pyroclastic flows from the 1991 eruption of Unzen volcano,Japan

Pyroclastic flows from Unzen were generated by gravitational collapse of the growing lava dome. As soon as the parental lobe failed at the edge of the dome, spontaneous shattering of lava occurred and induced a gravity flow of blocks and finer debris. The flows had a overhanging, tongue-like head and cone- or rollershaped vortices expanding outward and upward. Most of the flows traveled from 1 to 3 km, but some flows reached more than 4 km, burning houses and killing people in the evacuated zone of Kita-kamikoba on the eastern foot of the volcano. The velocities of the flows ranged from 15 to 25 m/s on the gentle middle flank. Observations of the flows and their deposits suggest that they consisted of a dense basal avalanche and an overlying turbulent ash cloud. The basal avalanche swept down a topographic low and formed to tongue-like lobe having well-defined levees; it is presumed to have moved as a non-Newtonian fluid. The measured velocities and runout distances of the flows can be matched to a Bingham model for the basal avalanche by the addition of turbulent resistance. The rheologic model parameters for the 29 May flow are as follows: the density is 1300 kg/m³, the yield strength is 850 Pa, the viscosity is 90 Pa s, and the thickness of the avalanche is 2 m. The ash cloud is interpreted as a turbulent mixing layer above the basal avalanche. The buoyant portions of the cloud produced ash-fall deposits, whereas the dense portions moved as a surge separated from the parental avalanche. The ash-cloud surges formed a wide devastated zone covered by very thin debris. The initial velocities of the 3 June surges, when they detached from avalanches, are determined by the runout distance and the angle of the energy-line slope. A comparison between the estimated velocities of the 3 June avalanches and the surges indicates that the surges that extended steep slopes along the avalanche path, detached directly from the turbulent heads of the avalanches. The over-running surge that reached Kita-Kamikoba had an estimated velocity higher than that of the avalanche; this farther-travelled surge is presumed to have been generated by collapse of a rising ash-cloud plume.     

Free precession of Cyg X-3 and the 34.1-day periodicity

The origin of the 34.1-day periodicity in X-ray and -ray from Cyg X-3 has not been made clear so far. In this paper, we propose a free precession model for an elastic neutron star. This model explains the 34.1-day periodicity and predicts the unobserved spin period for Cyg X-3 to be about 100 ms. Taking into account the possibility that the secular spin angular velocity of the star is different from that observed presently, the analogous long-terms periodicities of Her X-1 and Cen X-3 are also accounted for in this theory.     

Effects of the Chemical Compositions of Salars de Uyuni and Atacama Brines on Lithium Concentration during Evaporation

During Li recovery from salar brines, Li concentration is typically increased to about 60,000 mg L^?1 by evaporation. We investigated the concentration changes of Li, Na, K, Mg, Cl, SO₄, and B during evaporation of both natural Uyuni and artificial Atacama brines. The Uyuni brine exhibited a maximum Li concentration of 6810 mg L^?1 at 31 days of evaporation, at which point the majority of the Na and K in the brine was removed. The Li concentration decreased with further evaporation due to precipitation as Li₂SO₄, such that the level at the 56 day mark was approximately 4130 mg L^?1. In contrast, the artificial Atacama brine showed no pronounced Li precipitation, even after 54 days, at which point the Li concentration was 21,800 mg L^?1. The initial concentrations of Na and K in the Atacama brine were higher than those in the Uyuni brine, and the Atacama solution still retained K after 54 days of evaporation. The order of precipitation of cation species during the evaporation of both brines was: Na, followed by K, Mg, and Li. Thus, Li precipitation in the Atacama brine might be prevented due to the more favored precipitations of Na and K, such that significant Li removal did not occur in this brine.     

Wind-Tunnel Experiment on Logarithmic-Layer Turbulence under the Influence of Overlying Detached Eddies

A wind-tunnel experiment was carried out to test a hypothesis that the turbulence characteristics in the near-neutral surface layer are largely determined by detached eddies from above. The surrogate detached eddies were generated by using an active turbulence grid installed at the front of the test section and the parameters of the grid were chosen such that the fully developed logarithmic layer downstream consists of a turbulent flow that has similar normalized intensity to that typically observed in the near-neutral atmospheric surface layer. The effects of the detached eddies on turbulence characteristics were investigated by comparison with a second experiment without detached eddies. The influence of the detached eddies on the logarithmic layer was mostly on the coherent structures; the logarithmic layer with the detached eddies revealed a multi-layer structure similar to that found in the atmosphere where the lower part of the surface layer is dominated by sweep-like events and the upper part by ejection-like events. Our experiments show that the mean velocity gradient and the Reynolds shear stress were, however, not affected significantly by the detached eddies and hence the eddy viscosity.