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Volcanoes and Their Products
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Explosive eruptions do not produce lava but instead eject volcanic ash and coarser material into the air. The ejected material, no matter its size, is termed pyroclastic material, or sometimes simply ejecta. Ejecta ranges from fine ash, with grain size of millimeters or smaller, to large bombs and blocks, commonly 30 to 60 centimeters (1 to 2 feet) in diameter but occasionally up to 3.5 meters (12 feet). After it falls to Earth, ejecta may remain as unconsolidated pyroclastic debris termed tephra, or if hot enough, fuse together (consolidate) to produce a pyroclastic volcanic rock, so named because such rocks are formed from “fire” and contain clasts of material cemented together much like a sedimentary rock. Tuff is the general term for fine- to medium-grained pyroclastic rocks, and welded tuffs are tuffs that form (weld together) immediately during cooling after material settles to the ground. Every eruption produces some combination of lava flows and pyroclastics. The flows and pyroclastics may collect in one place, producing a classic volcano-shaped mountain—a steep-sided conical mountain with a crater on top.
Strength characteristics of crushable volcanic soils at various degrees of saturation
Published in Masayuki Hyodo, Hidekazu Murata, Yukio Nakata, Geomechanics and Geotechnics of Particulate Media, 2017
T. Ishikawa, S. Miura, S. Yokohama, R.G. Mijares
Test materials were taken from natural deposits of volcanic coarse-grained soils in the island of Hokkaido as shown in Figure 1. Pyroclastic fall deposit from the ejecta of Mashu volcano in the eastern region of Hokkaido comprises Touhoro volcanic soil samples. These volcanic soils deposited 11,000–13,000 years ago were taken from the sampling site in Touhoro District in the town of Nakashibetsu. Meanwhile, the eruption of Shikotsu caldera 31,000–34,000 years ago accumulated Tomikawa volcanic soil samples (Miura & Yagi, 2003). Belonging primarily to Shikotsu primary tephra, Tomikawa volcanic soils were extracted from the sampling site in Tomikawa District in the town of Monbetsu, 85 kilometers southeast of Sapporo.
Blast Physics and Vehicle Response
Published in Melanie Franklyn, Peter Vee Sin Lee, Military Injury Biomechanics, 2017
Stephen J. Cimpoeru, Paul Phillips, David V. Ritzel
An air-shock wave will also be driven ahead of the multiphase contact surface of the ejecta plume. Over a distance, away from the vehicle, the solid and gaseous phases of the plume will begin to separate, with the momentum of the larger clumps or solid particles causing them to be thrown ahead of the decelerating gas-dynamic contact surface of the fireball. However, in the blast flow regimes of relevance for vehicle damage, the air-shock wave and the dense high-speed multiphase ejecta plume will be closely coupled. The air-shock wave will impart loading when it reflects at and diffracts around the outside surface of the vehicle hull. Although the solid particulate does not technically exhibit ‘pressure’, the specific kinetic energy (defined earlier) of the particulate phase will inflict the equivalent of a dynamic pressure loading on any obstruction in the flow.
Geophysical constraints on the structure and formation of Onepoto, Orakei, Pupuke and Tank Farm maar volcanoes, Auckland Volcanic Field
Published in New Zealand Journal of Geology and Geophysics, 2019
Alan G. Nunns, Manfred P. Hochstein
The total volume of the Onepoto tuff ring was estimated as 9 × 106 m3 (using a representative topographic profile through gravity station B92). If the volume of the basalt sheet beneath the basin is added to the volume of the basin estimated from its anomalous mass, the total volume of displaced country rock is estimated at 107 m3. Taking into account the lower density of the tephra and the amount of basalt in the tephra, the estimated mass of country rock in the tephra ring is only about half the total mass displaced. The discrepancy is probably due to the following factors: (1) Onepoto crater was formed in a valley, hence less country rock than assumed was removed, (2) very fine ash was probably dispersed over a large area and has not been included in the estimate of the ejecta volume, and (3) considerable erosion of the tephra ring has probably occurred. Assuming that the true original volume of tephra was ∼2 × 107 m3 and that basalt made up ∼25% of ejecta, the volume of basaltic ejecta is ∼5 × 106 m3. Our estimated volume of basalt remaining beneath the crater is 4 × 106 m3 representing a roughly equal mass to the ejected basalt. As noted above, the actual excavated crater volume could be greater, with the additional volume occupied by unmagnetised relatively low-density pyroclastic rocks.
Middle–Upper Pleistocene tephras in the Papua New Guinea highlands
Published in Australian Journal of Earth Sciences, 2023
Tephra is an important product of volcanic eruptions. The word ‘tephra’ originates from the Greek word τεϕρα meaning ‘ashes’. The plural is either tephra or tephras—the former (as a singular collective noun) is more technically correct, but the latter avoids ambiguity and is in common usage (Alloway et al., 2007). As originally proposed (Thorarinsson, 1944), the term allows a distinction between tephra-fall deposits and tephra-flow deposits (see also Neuendorf et al., 2011). Here, ‘tephra’ is used for airfall volcanic ejecta, and tephra-flow materials are referred to as pyroclastic density current deposits (see Brown & Andrews, 2015).
Characterization of natural hydrocarbon seepage in the South Caspian Sea off Iran using satellite SAR and geological data
Published in Marine Georesources & Geotechnology, 2020
Andrei Yu. Ivanov, Hadi Gerivani, Natalia V. Evtushenko
The organic-rich sediments of Maykop Formation deposited during the Late Eocene-Early Miocene are the main source rocks in the southern Caspian Sea (Hudson et al. 2008; Afandiyeva, Rustam, and Johnson 2009). Analysis of the samples collected from outcrops, cores and mud-volcano ejecta shows that total organic carbon contents in the Maykop Series range from 1.2% to >10%. This formation, with thicknesses ranging from 100 m to >2500 m, forms the cores of many anticlines in the basin (Smith-Rouch 2006).