Transport Of Ejecta Research Articles

The dynamic floor of Yellowstone Lake, Wyoming, USA: The last 14 k.y. of hydrothermal explosions, venting, doming, and faulting

AbstractHydrothermal explosions are significant potential hazards in Yellowstone National Park, Wyoming, USA. The northern Yellowstone Lake area hosts the three largest hydrothermal explosion craters known on Earth empowered by the highest heat flow values in Yellowstone and active seismicity and deformation. Geological and geochemical studies of eighteen sublacustrine cores provide the first detailed synthesis of the age, sedimentary facies, and origin of multiple hydrothermal explosion deposits. New tephrochronology and radiocarbon results provide a four-dimensional view of recent geologic activity since recession at ca. 15–14.5 ka of the >1-km-thick Pinedale ice sheet.The sedimentary record in Yellowstone Lake contains multiple hydrothermal explosion deposits ranging in age from ca. 13 ka to ~1860 CE. Hydrothermal explosions require a sudden drop in pressure resulting in rapid expansion of high-temperature fluids causing fragmentation, ejection, and crater formation; explosions may be initiated by seismicity, faulting, deformation, or rapid lake-level changes. Fallout and transport of ejecta produces distinct facies of subaqueous hydrothermal explosion deposits. Yellowstone hydrothermal systems are characterized by alkaline-Cl and/or vapor-dominated fluids that, respectively, produce alteration dominated by silica-smectite-chlorite or by kaolinite. Alkaline-Cl liquids flash to steam during hydrothermal explosions, producing much more energetic events than simple vapor expansion in vapor-dominated systems. Two enormous explosion events in Yellowstone Lake were triggered quite differently: Elliott’s Crater explosion resulted from a major seismic event (8 ka) that ruptured an impervious hydrothermal dome, whereas the Mary Bay explosion (13 ka) was triggered by a sudden drop in lake level stimulated by a seismic event, tsunami, and outlet channel erosion.

Fingerprinting the Cretaceous-Paleogene boundary impact with Zn isotopes

Numerous geochemical anomalies exist at the K-Pg boundary that indicate the addition of extraterrestrial materials; however, none fingerprint volatilization, a key process that occurs during large bolide impacts. Stable Zn isotopes are an exceptional indicator of volatility-related processes, where partial vaporization of Zn leaves the residuum enriched in its heavy isotopes. Here, we present Zn isotope data for sedimentary rock layers of the K-Pg boundary, which display heavier Zn isotope compositions and lower Zn concentrations relative to surrounding sedimentary rocks, the carbonate platform at the impact site, and most carbonaceous chondrites. Neither volcanic events nor secondary alteration during weathering and diagenesis can explain the Zn concentration and isotope signatures present. The systematically higher Zn isotope values within the boundary layer sediments provide an isotopic fingerprint of partially evaporated material within the K-Pg boundary layer, thus earmarking Zn volatilization during impact and subsequent ejecta transport associated with an impact at the K-Pg.

Ejecta production from metal Sn into inert gases

Ejecta is produced from the shock-loaded perturbed surface of metals and subsequently breaks into small particles that are an important source of micro-particles/gas mixing during ejecta's transport and conversion. In engineering applications, the surrounding gas is often neglected during ejecta's formation, and many source models have been established based on the vacuum condition. However, the formation of the spike is always accompanied by gas, which has an important effect on the ejecta's mass/velocity distribution and the transformation time for a steady-state shock wave. To study the interaction between ejecta and ambient gases, we explore the ejecta production at the sinusoidal interface in the presence of argon gas. Six values of gas pressure and five interfaces were chosen to study the formation of the spike/micro-jet by using multi-component elastic–plastic hydro-dynamic codes. The results show that gas perturbed by the spike generated a precursory bow-shaped shock and gradually transformed into a plane wave. The transformation time was related to the velocity of the spike tip and the transmitted wave. The total mass of ejecta in gas had no distinct difference with that in vacuum, while it was significantly increased at the jet tip, which indicates that gas resistance reduced the spike velocity but did not influence the bubble. The initial velocity of the spike was insensitive to gas pressure but its decaying rate was positively correlated with gas pressure. As kh0 increased, the initial velocity of the spike tip and its decaying range increased, making it difficult to attain a steady state.

Shock-induced ejecta transport and breakup in reactive gas.

The transport process of micro-ejecta in reactive gases has recently attracted research attention and interest. Here, we investigate the interaction between shock-induced ejecta of Al and oxygen using a reactive molecular dynamics simulation. The results reveal that metal fragments ejected into reactive gases will quickly increase the temperature of the mixing zone, followed by the deceleration of spikes and a greater shock intensity in the compressed gases, compared with the ejection in inert gases. Moreover, we find that, in vacuum, only a small number of atoms fall out when spherical ejecta particles are finally formed. In the presence of inert gases, several small particles break away from the initial fragments during the transformation of the initially formed strip-shaped fragments into spherical particles, accompanying the detachment of a large number of atoms. When ejecta are transported in reactive gases, the chemical interactions cause more atoms to separate from particles, thus forming smaller fragments and more atomic particles. The research findings show that chemical reactions play an important role in ejecta transport and breakup, which should be considered in future ejecta-transport models for better predictions.

Application of photon Doppler velocimetry for characterization of ejecta from shock-loaded samples

We consider the problem of recovering the physical parameters of ejecta from data of photon Doppler velocimetry (PDV). The results of PDV measurements of ejecta production from shock-loaded Pb samples are presented. Shockwaves in the samples were generated by an accelerated flyer-plate. Depending on the sample thickness, the shock-breakout pressure varied from 27.5 to 43 GPa. The ejecta transport occurred in the air. The spectral profile J(ω) of heterodyne beats underlies our analysis of the experiments. The noise-free component of |J(ω)|2 is shown to obey the transport equation which accounts for multiple scattering and absorption of the probing beam in the cloud of moving particles. This provides a means for theoretical modeling of PDV data. Varying the values of the free-surface velocity and the parameters of the velocity distribution of ejecta, we fit the calculated spectrum to the PDV-measured one. We apply this method to time-resolved PDV spectra and, based on the ejecta optical model, recover the values of the free-surface velocity, the areal density, and the density-velocity distribution of ejecta.

Ejecta Production and Transport From a Shocked Sn Coupon

When a shock interacts with a Sn coupon, micrometer-scale particulate fragments, called ejecta, are usually formed and emitted from its free surface. Understanding the characteristics of such ejecta is of great importance in many fields. The velocity distribution and amount of particulate mass are directly dependent on several physical properties of the shock wave and shocked material states. In this paper, we numerically interrogate ejecta production and its dynamics for a wide range of shock loading conditions in a supported wave form and quantify the correlation of ejecta source with shock strength as well as surface roughness, which is represented by randomly perturbed surfaces and the one with a macrofeature superimposed. Furthermore, an unsteadiness-aware drag coefficient is discussed and implemented to accomplish ejecta transport studies.

Modeling the formation of the K–Pg boundary layer

In this paper we investigate the formation of the Cretaceous–Paleogene (K–Pg) boundary layer through numerical modeling. The K–Pg layer is widely agreed to be composed of meteoritic material and target rock from the Chicxulub impact site, that has been ejected around the globe and mixed with local material during final deposition. The observed composition and thickness of the K–Pg boundary layer changes with azimuth and distance from the impact site. We have run a suite of numerical simulations to investigate whether we can replicate the observational data, with a focus on the distal K–Pg layer and the impact glasses at proximal sites such as Beloc, Haiti. Previous models of the K–Pg ejecta have assumed an initial velocity distribution and tracked the ejecta to its final destination. Here, we attempt to model the entire process, from impact to the arrival of the ejecta around the globe. Our models replicate the observed ejecta thickness at proximal sites, and the modeled ejecta is composed of sediments and silicate basement rocks, in agreement with observational data. Models that use a 45° impact angle are able to replicate the total ejecta and iridium volume at distal sites, and the majority of the ejecta is composed of meteorite and target sediments. Sub-vertical impacts generate too little iridium, and oblique impacts of ⩽30 degrees generate too much. However, in contrast to observations, models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance, and are unable to transport shocked minerals (quartz and zircon) from the Chicxulub basement rocks around the globe. We suggest that much of the K–Pg ejecta is transported non-ballistically, and that the most plausible mechanism is through re-distribution from a hot, expanding atmosphere. The results are important for future investigations of the environmental effects of the Chicxulub impact.

Mineral-Produced High-Pressure Striae and Clay Polish: Key Evidence for Nonballistic Transport of Ejecta from Ries Crater

Recently discovered mineral-produced, deeply incised striae and mirrorlike polish on broken surfaces of limestone fragments from the sedimentary ejecta of the Ries impact crater of southern Germany are described. The striae and polish were produced under high confining pressures during high-velocity nonballistic transport of the ejecta mass within the time span of the cratering event (measured in terms of seconds). The striae on these fragments were produced by scouring by small mineral grains embedded in the surrounding clay matrix, and the polish was formed under the same condition, by movements of relatively fragment-free clay against the fragment surfaces. The occurrence of these striae and polish is key evidence for estimating the distribution and determining the relative importance of nonballistic and ballistic transport of ejecta from the shallow Ries stony meteorite impact crater.

Mineral-Produced High-Pressure Striae and Clay Polish: Key Evidence for Nonballistic Transport of Ejecta from Ries Crater

Recently discovered mineral-produced, deeply incised striae and mirror-like polish on broken surfaces of limestone fragments from the sedimentary ejecta of the Ries impact crater of southern Germany are described. The striae and polish were produced under high confining pressures during high-velocity nonballistic transport of the ejecta mass within the time span of the cratering event (measured in terms of seconds). The striae on these fragments were produced by scouring by small mineral grains embedded in the surrounding clay matrix, and the polish was formed under the same condition, by movements of relatively fragment-free clay against the fragment surfaces. The occurrence of these striae and polish is key evidence for estimating the distribution and determining the relative importance of nonballistic and ballistic transport of ejecta from the shallow Ries stony meteorite impact crater.