146 results found
Monteux J, Collins GS, Tobie G, et al., 2015, Consequences of large impacts on Enceladus' core shape, Icarus, Vol: 264, Pages: 300-310, ISSN: 1090-2643
The intense activity on Enceladus suggests a differentiated interior consisting of a rocky core, an internal ocean and an icy mantle. However, topography and gravity data suggests large heterogeneity in the interior, possibly including significant core topography. In the present study, we investigated the consequences of collisions with large impactors on the core shape. We performed impact simulations using the code iSALE2D considering large differentiated impactors with radius ranging between 25 and 100 km and impact velocities ranging between 0.24 and 2.4 km/s. Our simulations showed that the main controlling parameters for the post-impact shape of Enceladus’ rock core are the impactor radius and velocity and to a lesser extent the presence of an internal water ocean and the porosity and strength of the rock core. For low energy impacts, the impactors do not pass completely through the icy mantle. Subsequent sinking and spreading of the impactor rock core lead to a positive core topographic anomaly. For moderately energetic impacts, the impactors completely penetrate through the icy mantle, inducing a negative core topography surrounded by a positive anomaly of smaller amplitude. The depth and lateral extent of the excavated area is mostly determined by the impactor radius and velocity. For highly energetic impacts, the rocky core is strongly deformed, and the full body is likely to be disrupted. Explaining the long-wavelength irregular shape of Enceladus’ core by impacts would imply multiple low velocity (<2.4 km/s) collisions with deca-kilometric differentiated impactors, which is possible only after the LHB period.
Potter RWK, Kring DA, Collins GS, 2015, Scaling of basin-sized impacts and the influence of target temperature, Geological Society of America Special Papers, Vol: 518, Pages: 99-113, ISSN: 0072-1077
We produce a set of scaling laws for basin-sized impacts using data from a suiteof lunar basin numerical models. The results demonstrate the importance of preimpacttarget temperature and thermal gradient, which are shown to greatly infl uencethe modifi cation phase of the impact cratering process. Impacts into targets withcontrasting thermal properties also produce very different crustal and topographicprofi les for impacts of the same energy. Thermal conditions do not, however, signifi -cantly infl uence the excavation stage of the cratering process; results demonstrate,as a consequence of gravity-dominated growth, that transient crater radii are generallywithin 5% of each other over a wide range of thermal gradients. Excavationdepth-to-diameter ratios for the basin models (~0.12) agree well with experimental,geological, and geophysical estimates, suggesting basins follow proportional scaling.This is further demonstrated by an agreement between the basin models andPi- scaling laws based upon fi rst principles and experimental data. The results of thiswork should also be applicable to basin-scale impacts on other silicate bodies, includingthe Hadean Earth.
Forman LV, Bland PA, Timms NE, et al., 2015, RECOVERING THE PRIMORDIAL IMPACT HISTORY OF CHONDRITES IN UNPRECEDENTED DETAIL USING MASSIVE EBSD DATASETS, 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, ISSN: 1086-9379
Muxworthy AR, Bland PA, Collins G, et al., 2015, MAGNETIC FABRICS IN ALLENDE: IMPLICATIONS FOR MAGNETIC REMANENCE ACQUISITION., 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, ISSN: 1086-9379
Miljkovic K, Wieczorek MA, Collins GS, et al., 2015, Excavation of the lunar mantle by basin-forming impact events on the Moon, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 409, Pages: 243-251, ISSN: 0012-821X
Jacobs CT, Goldin TJ, Collins GS, et al., 2015, An improved quantitative measure of the tendency for volcanic ash plumes to form in water: implications for the deposition of marine ash beds, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, Vol: 290, Pages: 114-124, ISSN: 0377-0273
Collins GS, 2015, Rock Avalanche, Encyclopedia of Planetary Landforms, Publisher: Springer New York, Pages: 1807-1811, ISBN: 9781461431336
Potter RWK, Kring DA, Collins GS, 2015, Scaling of basin-sized impacts and the influence of target temperature, Geological Society of America Special Papers, Publisher: Geological Society of America, Pages: 99-113, ISBN: 9780813725185
Collins GS, 2014, Numerical simulations of impact crater formation with dilatancy, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 119, Pages: 2600-2619, ISSN: 2169-9097
Bland PA, Collins GS, Davison TM, et al., 2014, Pressure-temperature evolution of primordial solar system solids during impact-induced compaction, NATURE COMMUNICATIONS, Vol: 5, ISSN: 2041-1723
Davison TM, Cielsa FJ, Collins GS, et al., 2014, The effect of impact obliquity on shock heating in planetesimal collisions, Meteoritics & Planetary Science, Vol: 49, Pages: 2252-2265, ISSN: 1086-9379
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, 11th World Congress on Computational Mechanics (WCCM) / 5th European Conference on Computational Mechanics (ECCM) / 6th European Conference on Computational Fluid Dynamics (ECFD), Publisher: INT CENTER NUMERICAL METHODS ENGINEERING, Pages: 7406-7417
Collins GS, 2014, Terraced Crater Wall (Mass Wasting), Encyclopedia of Planetary Landforms, Publisher: Springer New York, Pages: 1-6
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.
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
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