Incorporation of radioactive waste in basalt magma is controlled by the dimensions of basalt dikes at repository depths and the depth of magma fragmentation. Local sheet-like intrusions formed at depths of 200 to more » 300 m probably due to a combination of extensional faulting during emplacement and trapping within low-density tuff country rock, aided in part by a low magma-volatile content. Basalt centers are fed from narrow linear dikes. Theoretical considerations suggest basalt magma ascends rapidly from mantle depth (10`s of cm/sec in the bubble-free regime) but may be trapped temporarily and fractionate at the mantle/crust interface. Consequence studies, the emphasis of this work, are evaluated by tracing the steps of ascent of basaltic magma including intersection and disruption of a repository followed by surface eruption. Volcanic hazard studies, combining standard techniques of hazard appraisal and risk assessment are being undertaken with respect to storage of high-level, radioactive waste in southern Nevada. Liberation of poisonous gases by the early sill intrusions explains why the mid-Capitanian global biota crisis preceded the peak ELIP eruption by 2–3 m.y. A zone of higher velocity but less-negative radial anisotropy, on the hotspot track but to the northeast of the eruption center in the Panxi region, reflects an elevated proportion of sills emplaced at the incipient stage of the ELIP. We further propose that the anomaly represents a hidden hotspot track that was emplaced before the ELIP eruption. We rule out the possibilities of rifting or orogenesis to explain these seismic characteristics and interpret the seismic anomaly as a mafic-ultramafic, dike-dominated magma storage system of the ELIP. We find a northeast-trending zone of high shear-wave velocity (Vs) and negative radial anisotropy (Vsv > Vsh v more » and h are vertically and horizontally polarized S waves, respectively) in the crust and lithosphere. We use surface-wave tomography to image the lithosphere under the Permian Emeishan large igneous province (ELIP) in southwestern China. Therefore, the structure of LIPs' magma storage system is critical because it dictates the occurrence and timing of mass extinction. It has been proposed that the environmental impacts are primarily related to sill emplacement. However, the precise relations between LIPs and their impacts on biodiversity is enigmatic, given that they can be asynchronous. Large igneous provinces (LIPs) are commonly associated with mass extinctions. The presence of extremely long lava flows and sinuous rilles on the moon has often been cited as evidence for very high extrusion rates and thus a basic difference between terrestrial and lunar magmas and crustal environments. Terrestrial fire fountain heights up to 500 m imply the release of up to 0.4 wt % water from the magma, corresponding to initial water contents up to 0.6 wt %. Terrestrial fire fountain heights are dictated by the vertical velocity of the magma/gas dispersion emerging through the vent, increasing with increasing magma gas content and mass eruption rate, and decreasing with increasing magma viscosity. For commonly occuring lunar and terrestrial basalts the magma rise speed must be greater than 0.5-1 m/s if strombolian activity is to be avoided and relatively steady fire fountaining is to take place. As the magma nears the surface, bubble coalescence will tend to occur, leading to intermittent explosive strombolian-style activity. Fissure widths of about 4 m would be needed to account for output rates estimated for the Columbia River flood basalt eruptions. For terestrial basalts with negligible yield strengths and viscosities more » greater than 10/sup 2/ Ps s, widths in the range 0.2-0.6 m are needed to allow eruptions from between depths of 0.5-20 km. Magma ascent is related to dike or conduit width. Mathematical models of the nature and motion of gas/liquid mixtures are developed and show that gas exsolution from terrestrial and lunar magmas commonly only occurs at shallow depths (less than 2 km) thus the ascent of bubble-free magma at depth can be treated separately from the complex motions caused by gas exsolution near the surface. Geological and physical observations and constraints are applied to the development of a model of the ascent and emplacement of basaltic magma on the earth and moon.
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