ejecta

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      Ejecta (from Latin 'things thrown out'; singular ejectum) are particles ejected from an area. In volcanology, in particular, the term refers to particles including pyroclastic materials (tephra) that came out of a volcanic explosion and magma eruption volcanic vent, or crater, has traveled through the air or under water, and fell back on the ground surface or on the ocean floor.


      Volcanology


      Typically in volcanology, ejecta is a result of explosive eruptions. In an explosive eruption, large amounts of gas are dissolved in extremely viscous lava; this lava froths to the surface until the material is expelled rapidly due to the trapped pressure. Sometimes in such an event a lava plug or volcanic neck forms from lava that solidifies inside a volcano's vent, causing heat and pressure to build up to an extreme with no way to escape. When the blockage breaks and cannot sustain itself any longer, a more violent eruption occurs, which allows materials to be ejected out of the volcano.
      Ejecta can consist of:

      juvenile particles – (fragmented magma and free crystals)
      cognate or accessory particles – older volcanic rocks from the same volcano
      accidental particles – derived from the rocks under the volcano
      These particles may vary in size; tephra can range from ash (<1/10 inch [0.25 cm]) or lapilli (little stones from 1/10 to 2+1⁄2 inches or 0.25 to 6.35 centimetres) to volcanic bombs (>2.5 inches [6.4 cm]).


      Planetary geology



      In planetary geology, the term "ejecta" includes debris ejected during the formation of an impact crater.
      When an object massive enough hits another object with enough force, it creates a shockwave that spreads out from the impact. The object breaks and excavates into the ground and rock, at the same time spraying material known as impact ejecta. This ejecta is distributed outward from the crater's rim onto the surface as debris; it can be loose material or a blanket of debris, which thins at the outermost regions.
      Ejecta features are classified based on their distance from the impact crater, the appearance of the ejected material, and the geomorphological characteristics of the terrain. Some common ejecta features include ejecta blankets, radial and concentric ejecta patterns, and secondary craters.
      Ejecta Blankets: Ejecta blankets are the continuous layer of debris that surrounds the impact crater, thinning outwards from the crater's rim. The composition of the ejecta blanket can provide valuable information about the geological composition of the impacted surface and the projectile that caused the impact. The distribution and morphology of the ejecta blanket can also provide insight into the impact angle and the dynamics of the ejecta emplacement process.
      Radial and Concentric Ejecta Patterns: Radial ejecta patterns are characterized by the outward distribution of ejecta from the crater in a series of rays or streaks. These rays are often more prominent in craters formed on solid surfaces, such as the Moon or Mercury. Concentric ejecta patterns are characterized by the presence of multiple, circular layers of ejecta surrounding the impact crater. These patterns are commonly observed on icy surfaces, such as the moons of Jupiter and Saturn, and are indicative of the presence of subsurface volatiles, like water or other ices.
      If enough ejecta are deposited around an impact crater, it can form an ejecta blanket; this blanket is full of dust and debris that originated from the initial impact. The size of this impact crater along with the ejecta blanket can be used to determine the size and intensity of the impacting object. On earth, these ejecta blankets can be analyzed to determine the source location of the impact.
      A lack of impact ejecta around the planet Mars's surface feature Eden Patera was one of the reasons for suspecting in the 2010s that it is a collapsed volcanic caldera and not an impact crater.


      Astronomy and heliophysics


      In astrophysics or heliophysics, ejecta refers to material expelled in a stellar explosion as in a supernova or in a coronal mass ejection (CME).


      Artificial



      Beside material launched by humans into space with a range of launch systems, some instances particularly nuclear produce artificial ejecta, like in the case of the Pascal-B test which might have ejected an object with a speed of Earth's escape velocity into space.


      References

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    Ejecta from impact craters - ScienceDirect

    Jan 1, 2011 · Ejecta were collected in bins at various distances from the impact. The observed nearly-90° ejection angle and the fall-distance to the chamber floor were used to calculate the ejection velocity of material in the collection bins. The …

    Ejecta - an overview | ScienceDirect Topics

    The rock avalanche/ ejecta (RAEJ) documented by Crosta et al. (2018a, b) represent peculiar types of landslides that can be found on Mars but are unknown on Earth (Fig. 14). These landslides initially acquired momentum by asteroid impact and started as impact ejecta or as destabilization of slope masses directly neighboring the impact crater ...

    Ejecta - an overview | ScienceDirect Topics

    Martian ejecta blankets often indicate extensive ground-hugging flow away from the crater, most likely due to groundwater or melted ice in the ejecta. Extensive, runout ejecta flows exist on Venus, thought to be due to entrained atmosphere or an enhanced fraction of impact melt in the ejecta (due to the high surface temperatures of Venusian ...

    Measuring ejecta characteristics and momentum transfer in …

    Mar 1, 2019 · As an example, Fig. 3 shows the ejecta velocity histogram with cumulative size distribution for a Cu projectile impacting on a sandstone target. A luminescent transient plasma plume followed by a steepening ejecta cone and completed by the detachment of spall fragments characterizes the typical evolution of ejecta [12]. The high-speed camera ...

    Ejecta distribution and momentum transfer from oblique impacts …

    Mar 1, 2022 · The amount by which crater ejecta enhances asteroid deflection—that is, the momentum of the crater ejecta that escapes the gravitational attraction of the target body divided by the impactor momentum (β − 1)—has been found to vary significantly depending on the target asteroid’s properties, composition and structure (e.g., Jutzi and ...

    Precambrian impact structures and ejecta on earth: A review

    Sep 1, 2024 · Distal ejecta make up about 10 % of the total ejecta and consist primarily of material that is highly shock metamorphosed, melted or vaporized and can be found in ejecta blankets from impact events throughout Earth’s geologic history (e.g., Glass and Simonson, 2013). During this process, ejected (ballistic) melt rapidly cools to form non ...

    Ejecta behavior during plume-surface interactions under rarefied ...

    May 1, 2024 · Ejecta with Stokes number S t k ≪ 1 is expected to follow the flow, whereas ejecta with S t k ≫ 1 has a motion independent of the surrounding flow field. The Stokes number for the mean size of the ejecta and the range of velocities is S t k ≈ 5500, which implies that the ejecta would follow a ballistic path given an initial momentum impulse.

    Impact ejecta emplacement on terrestrial planets

    Oct 15, 2011 · Ejecta deposits very poorly exposed and eroded in close proximity to the crater rim. In the Tyasmin River valley ~ 6–8 km outside the crater rim, low shock, melt-free “monomict” breccias are overlain by polymict breccias (Gurov et al., 2003). Both breccias comprise crystalline rocks; polymict breccias contain more highly shocked material.

    New morphological mapping and interpretation of ejecta deposits …

    Jan 1, 2018 · The various ejecta facies were then examined in more detail using ∼0.5–1 m per pixel LROC Narrow Angle Camera (NAC) images (Robinson et al., 2010) to better define the facies boundaries and focus in on specific details and areas of interest. The individual images used to observe the morphology of Orientale ejecta were selected based on ...

    Microscopic ejecta measurements from hypervelocity impacts on …

    Jun 1, 2021 · We address the latter with measurements of the microscopic ejecta distribution produced by light gas gun impacts on solid aluminum and powdered regolith simulant targets. We examine both the size and shape of the ejecta using thin-film witness plates and find that the size distributions of microscopic ejecta follow power laws.