135 results found
Hill J, Collins GS, Avdis A, et al., 2014, How does multiscale modelling and inclusion of realistic palaeobathymetry affect numerical simulation of the Storegga Slide tsunami?, Ocean Modelling, Vol: 83, Pages: 11-25, ISSN: 1463-5003
The ∼8.15 ka Storegga submarine slide was a large (∼3000 km3), tsunamigenic slide off the coast of Norway. The resulting tsunami had run-up heights of around 10–20 m on the Norwegian coast, over 12 m in Shetland, 3–6 m on the Scottish mainland coast and reached as far as Greenland. Accurate numerical simulations of Storegga require high spatial resolution near the coasts, particularly near tsunami run-up observations, and also in the slide region. However, as the computational domain must span the whole of the Norwegian-Greenland sea, employing uniformly high spatial resolution is computationally prohibitive. To overcome this problem, we present a multiscale numerical model of the Storegga slide-generated tsunami where spatial resolution varies from 500 m to 50 km across the entire Norwegian-Greenland sea domain to optimally resolve the slide region, important coastlines and bathymetric changes. We compare results from our multiscale model to previous results using constant-resolution models and show that accounting for changes in bathymetry since 8.15 ka, neglected in previous numerical studies of the Storegga slide-tsunami, improves the agreement between the model and inferred run-up heights in specific locations, especially in the Shetlands, where maximum run-up height increased from 8 m (modern bathymetry) to 13 m (palaeobathymetry). By tracking the Storegga tsunami as far south as the southern North sea, we also found that wave heights were high enough to inundate Doggerland, an island in the southern North Sea prior to sea level rise over the last 8 ka.
Miljković K, Collins GS, Bland PA, 2014, Reply to comment on: “Supportive comment on: “Morphology and population of binary asteroid impact craters”, by K. Miljković, G.S. Collins, S. Mannick and P.A. Bland – An updated assessment”, Earth and Planetary Science Letters, Vol: 405, Pages: 285-286, ISSN: 0012-821X
In Miljković et al. (2013) we resolved the apparent contradiction that while 15% of the Near Earth Asteroid (impactor) population are binaries, only 2–4% of craters formed on Earth and Mars (target planet) are doublet craters. Using 3D hydrocode simulations to explore the physics of binary impacts, we showed that only 2% of binary asteroid impacts produced well-separated doublets, while the rest covered morphologies ranging from overlapping to elliptical or even circular. We then generated a complete classification dataset to aid in the identification of the (sometimes subtle) morphological characteristics consistent with a binary asteroid impact. We thank Schmieder et al. (2013) for providing additional detailed geochronological constraints which indicate that our lower bound of 2% doublet craters on Earth may in fact be ≤1.5%.
Milbury C, Johnson BC, Melosh HJ, et al., 2014, THE EFFECT OF POROSITY AND DILATANCY ON THE GRAVITY SIGNATURE OF CRATERS ON THE MOON., 77th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A283-A283, ISSN: 1086-9379
Bray VJ, Collins GS, Morgan JV, et al., 2014, Hydrocode simulation of Ganymede and Europa cratering trends - How thick is Europa's crust?, ICARUS, Vol: 231, Pages: 394-406, ISSN: 0019-1035
Neal WD, Appleby-Thomas GJ, Collins GS, 2014, Meso-scopic deformation in brittle granular materials, 18TH APS-SCCM AND 24TH AIRAPT, PTS 1-19, Vol: 500, ISSN: 1742-6588
Jacobs CT, Collins GS, Piggott MD, et al., 2014, Multiphase flow modelling of explosive volcanic eruptions using an adaptive unstructured mesh-based approach, Pages: 7406-7417
Explosive volcanic eruption events, in which large quantities of hot gas and ash are expelled high into the atmosphere, are one of the most powerful natural hazards. In order to gain a full understanding of the dangers these eruptions pose, their complex multiscale and multiphase nature must be captured to a high degree of accuracy. The application of numerical multiphase flow models often represents the only tenable way of achieving this, and permits the investigation of ash cloud evolution in domains many times larger than the laboratory-scale. However, even the most advanced models of eruption dynamics are restricted by the fixed mesh-based approaches that they generally employ. The research presented herein introduces a compressible multiphase flow model recently implemented within Fluidity, a combined finite element / control volume CFD code, for the study of explosive volcanic eruptions. Fluidity adopts an adaptive unstructured mesh-based approach to discretise the domain and focus numerical resolution only in areas important to the dynamics, while decreasing resolution where it is not needed as a simulation progresses. This allows the accurate but economical representation of the flow dynamics throughout time. The application of the model considers a 7 km × 7 km domain in which the violent eruption of hot gas and volcanic ash high into the atmosphere is simulated. It is shown by a convergence analysis that Fluidity offers the same solution accuracy for reduced computational cost using an adaptive unstructured mesh, compared to the same simulation performed with a fixed uniform mesh.
Ciesla FJ, Davison TM, Collins GS, et al., 2013, Thermal consequences of impacts in the early Solar System., Meteoritics and Planetary Science, Vol: 48, Pages: 2559-2567, ISSN: 1086-9379
Miljkovic K, Wieczorek MA, Collins GS, et al., 2013, Asymmetric Distribution of Lunar Impact Basins Caused by Variations in Target Properties, Science, Vol: 342, Pages: 724-726, ISSN: 0036-8075
Maps of crustal thickness derived from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission revealed more large impact basins on the nearside hemisphere of the Moon than on its farside. The enrichment in heat-producing elements and prolonged volcanic activity on the lunar nearside hemisphere indicate that the temperature of the nearside crust and upper mantle was hotter than that of the farside at the time of basin formation. Using the iSALE-2D hydrocode to model impact basin formation, we found that impacts on the hotter nearside would have formed basins with up to twice the diameter of similar impacts on the cooler farside hemisphere. The size distribution of lunar impact basins is thus not representative of the earliest inner solar system impact bombardment.
Davison TM, O'Brien DP, Ciesla FJ, et al., 2013, The early impact histories of meteorite parent bodies, Meteoritics and Planetary Science, Vol: 48, Pages: 1894-1918, ISSN: 1086-9379
We have developed a statistical framework that uses collisional evolution models, shock physics modeling and scaling laws to determine the range of plausible collisional histories for individual meteorite parent bodies. It is likely that those parent bodies that were not catastrophically disrupted sustained hundreds of impacts on their surfaces — compacting, heating, and mixing the outer layers; it is highly unlikely that many parent bodies escaped without any impacts processing the outer few kilometers. The first 10 - 20 Myr were the most important time for impacts, both in terms of the number of impacts and the increase of specific internal energy due to impacts. The model has been applied to evaluate the proposed impact histories of several meteorite parent bodies: up to 10 parent bodies that were not disrupted in the first 100 Myr experienced a vaporizing collision of the type necessary to produce the metal inclusions and chondrules on the CB chondrite parent; around 1 -- 5\% of bodies that were catastrophically disrupted after 12 Myr sustained impacts at times that match the heating events recorded on the IAB/winonaite parent body; more than 75\% of 100 km radius parent bodies which survived past 100 Myr without being disrupted sustained an impact that excavates to the depth required for mixing in the outer layers of the H chondrite parent body; and to protect the magnetic field on the CV chondrite parent body, the crust would have had to have been thick (~ 20 km) in order to prevent it being punctured by impacts.
Bland PA, Collins GS, Dyl KA, et al., 2013, Impact-induced compaction of primordial materials and the effect on the chondrite record., 76th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A63-A63, ISSN: 1086-9379
Oishi Y, Piggott MD, Maeda T, et al., 2013, Three-dimensional tsunami propagation simulations using an unstructured mesh finite element model, Journal of Geophysical Research: Solid Earth, Vol: 118, Pages: 2998-3018, ISSN: 2169-9313
Miljković K, Collins GS, Mannick S, et al., 2013, Morphology and population of binary asteroid impact craters, Earth and Planetary Science Letters, Vol: 363, Pages: 121-132, ISSN: 0012-821X
Observational data show that in the Near Earth Asteroid (NEA) region 15% of asteroids are binary. However, the observed number of plausible doublet craters is 2–4% on Earth and 2–3% on Mars. This discrepancy between the percentage of binary asteroids and doublets on Earth and Mars may imply that not all binary systems form a clearly distinguishable doublet crater owing to insufficient separation between the binary components at the point of impact. We simulate the crater morphology formed in close binary asteroid impacts in a planetary environment and the range of possible crater morphologies includes: single (circular or elliptical) craters, overlapping (tear-drop or peanut shaped) craters, as well as clearly distinct, doublet craters. While the majority of binary asteroids impacting Earth or Mars should form a single, circular crater, about one in four are expected to form elongated or overlapping impact craters and one in six are expected to be doublets. This implies that doublets are formed in approximately 2% of all asteroid impacts on Earth and that elongated or overlapping binary impact craters are under-represented in the terrestrial crater record. The classification of a complete range of binary asteroid impact crater structures provides a template for binary asteroid impact crater morphologies, which can help in identifying planetary surface features observed by remote sensing.
Collins GS, Wuennemann K, Artemieva N, et al., 2013, Numerical modelling of impact processes, Impact Cratering: Processes and Products, Editors: Osinski, Pierazzo, Publisher: Wiley-Blackwell, ISBN: 9781405198295
Kenkmann T, Collins GS, Wuennemann K, 2013, The modification stage of crater formation, Impact Cratering: Processes and Products, Editors: Osinski, Pierazzo, Publisher: Wiley-Blackwell, ISBN: 9781405198295
Potter RWK, Collins GS, 2013, Numerical modeling of asteroid survivability and possible scenarios for the Morokweng crater-forming impact, Meteoritics & Planetary Science, Vol: 48, Pages: 744-757, ISSN: 1945-5100
Elbeshausen D, Wünnemann K, Collins GS, 2013, The transition from circular to elliptical impact craters, Journal of Geophysical Research: Planets, Vol: 118, Pages: 2295–2309-2295–2309, ISSN: 2169-9100
Elliptical impact craters are rare among the generally symmetric shape of impact structures on planetary surfaces. Nevertheless, a better understanding of the formation of these craters may significantly contribute to our overall understanding of hypervelocity impact cratering. The existence of elliptical craters raises a number of questions: Why do some impacts result in a circular crater whereas others form elliptical shapes? What conditions promote the formation of elliptical craters? How does the formation of elliptical craters differ from those of circular craters? Is the formation process comparable to those of elliptical craters formed at subsonic speeds? How does crater formation work at the transition from circular to elliptical craters? By conducting more than 800 three-dimensional (3-D) hydrocode simulations, we have investigated these questions in a quantitative manner. We show that the threshold angle for elliptical crater generation depends on cratering efficiency. We have analyzed and quantified the influence of projectile size and material strength (cohesion and coefficient of internal friction) independently from each other. We show that elliptical craters are formed by shock-induced excavation, the same process that forms circular craters and reveal that the transition from circular to elliptical craters is characterized by the dominance of two processes: A directed and momentum-controlled energy transfer in the beginning and a subsequent symmetric, nearly instantaneous energy release.
Potter RWK, Kring DA, Collins GS, 2013, Quantifying the attenuation of structural uplift beneath large lunar craters, Geophysical Research Letters, Vol: 40, Pages: 5615–5620-5615–5620, ISSN: 1944-8007
Terrestrial crater observations and laboratory experiments demonstrate that target material beneath complex impact craters is uplifted relative to its preimpact position. Current estimates suggest maximum uplift is one tenth of the final crater diameter for terrestrial complex craters and one tenth to one fifth for lunar central peak craters. These latter values are derived from an analytical model constrained by observations from small craters and may not be applicable to larger complex craters and basins. Here, using numerical modeling, we produce a set of relatively simple analytical equations that estimate the maximum amount of structural uplift and quantify the attenuation of uplift with depth beneath large lunar craters.
Potter RWK, Kring DA, Collins GS, et al., 2013, Numerical modeling of the formation and structure of the Orientale impact basin, Journal of Geophysical Research: Planets, Pages: n/a-n/a, ISSN: 2169-9100
Jacobs CT, Collins GS, Piggott MD, et al., 2013, Multiphase flow modelling of volcanic ash particle settling in water using adaptive unstructured meshes, Geophysical Journal International, Vol: 192, Pages: 647-665
Small-scale experiments of volcanic ash particle settling in water have demonstrated that ash particles can either settle slowly and individually, or rapidly and collectively as a gravitationally unstable ash-laden plume. This has important implications for the emplacement of tephra deposits on the seabed. Numerical modelling has the potential to extend the results of laboratory experiments to larger scales and explore the conditions under which plumes may form and persist, but many existing models are computationally restricted by the fixed mesh approaches that they employ. In contrast, this paper presents a new multiphase flow model that uses an adaptive unstructured mesh approach. As a simulation progresses, the mesh is optimized to focus numerical resolution in areas important to the dynamics and decrease it where it is not needed, thereby potentially reducing computational requirements. Model verification is performed using the method of manufactured solutions, which shows the correct solution convergence rates. Model validation and application considers 2-D simulations of plume formation in a water tank which replicate published laboratory experiments. The numerically predicted settling velocities for both individual particles and plumes, as well as instability behaviour, agree well with experimental data and observations. Plume settling is clearly hindered by the presence of a salinity gradient, and its influence must therefore be taken into account when considering particles in bodies of saline water. Furthermore, individual particles settle in the laminar flow regime while plume settling is shown (by plume Reynolds numbers greater than unity) to be in the turbulent flow regime, which has a significant impact on entrainment and settling rates. Mesh adaptivity maintains solution accuracy while providing a substantial reduction in computational requirements when compared to the same simulation performed using a fixed mesh, highlighting the benefits of an adapt
Potter RWK, Kring DA, Collins GS, et al., 2012, Estimating transient crater size using the crustal annular bulge: Insights from numerical modeling of lunar basin-scale impacts, GEOPHYSICAL RESEARCH LETTERS, Vol: 39, ISSN: 0094-8276
Smith A, Crawford IA, Gowen RA, et al., 2012, Lunar Net-a proposal in response to an ESA M3 call in 2010 for a medium sized mission, EXPERIMENTAL ASTRONOMY, Vol: 33, Pages: 587-644, ISSN: 0922-6435
Collins GS, 2012, Moonstruck magnetism, Science, Vol: 335, Pages: 1176-1177
Collins GS, Melosh HJ, Osinski GR, 2012, The Impact-Cratering Process, ELEMENTS, Vol: 8, Pages: 25-30, ISSN: 1811-5209
Miljkovic K, Collins GS, Chapman DJ, et al., 2012, HIGH-VELOCITY IMPACTS IN POROUS SOLAR SYSTEM MATERIALS, 7th Biennial Conference of the American-Physical-Society-Topical-Group on Shock Compression of Condensed Matter, Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Davison TM, Ciesla FJ, Collins GS, 2012, Post-Impact Thermal Evolution of Porous Planetesimals, Geochimica et Cosmochimica Acta, Vol: 95, Pages: 252-269, ISSN: 0016-7037
Bray VJ, Schenk PM, Melosh HJ, et al., 2012, Ganymede crater dimensions – Implications for central peak and central pit formation and development, Icarus, Vol: 217, Pages: 115-129
The morphology of impact craters on the icy Galilean satellites differs from craters on rocky bodies. Thedifferences are thought due to the relative weakness of ice and the possible presence of sub-surface waterlayers. Digital elevation models constructed from Galileo images were used to measure a range of dimensionsof craters on the dark and bright terrains of Ganymede. Measurements were made from multipleprofiles across each crater, so that natural variation in crater dimensions could be assessed and averagedscaling trends constructed. The additional depth, slope and volume information reported in this work hasenabled study of central peak formation and development, and allowed a quantitative assessment of thevarious theories for central pit formation. We note a possible difference in the size-morphology progressionbetween small craters on icy and silicate bodies, where central peaks occur in small craters beforethere is any slumping of the crater rim, which is the opposite to the observed sequence on the Moon. Conversely,our crater dimension analyses suggest that the size-morphology progression of large lunar cratersfrom central peak to peak-ring is mirrored on Ganymede, but that the peak-ring is subsequentlymodified to a central pit morphology. Pit formation may occur via the collapse of surface material intoa void left by the gradual release of impact-induced volatiles or the drainage of impact melt intosub-crater fractures.
Potter RWK, Collins GS, Kiefer WS, et al., 2012, Constraining the size of the South Pole-Aitken basin impact, Icarus, Vol: 220, Pages: 730 - 743-730 - 743, ISSN: 0019-1035
Davison TM, Collins GS, Elbeshausen D, et al., 2011, Numerical modeling of oblique hypervelocity impacts on strong ductile targets, METEORITICS & PLANETARY SCIENCE, Vol: 46, Pages: 1510-1524, ISSN: 1086-9379
Collins GS, Elbeshausen D, Davison TM, et al., 2011, The size-frequency distribution of elliptical impact craters, Earth and Planetary Science Letters, Vol: 310, Pages: 1-8, ISSN: 0012-821X
Miljkovic K, Mannick S, Collins GS, et al., 2011, HYDROCODE SIMULATIONS OF BINARY ASTEROID IMPACTS, 74th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, Pages: A161-A161, ISSN: 1086-9379
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