Crater Slopes Research Articles

Glacial sculpting of a martian cratered landscape on the northeastern flank of the Hellas basin

The interiors and exteriors of the >25 km diameter Batson, Nako, Salkhad, and Jori craters (and McCauley crater to a lesser degree) on the northeastern rim of Hellas basin, Mars, were extensively modified by glacio-fluvial and glacio-lacustrine activity during the Middle and Late Amazonian, from some time before 1.4 Ga to the present as revealed by CTX, HiRISE, and CaSSIS observations. This work presents extensive descriptions and discussions of individual candidate glacial and glaciofluvial landforms associated with cratered landscapes, as well as their spatial association. We also present absolute age dates and a relative sequence of events, followed by a possible environmental reconstruction, involving a regional ice cover, subglacial meltwater, and ice-covered lakes. On crater interiors, inferred glacial modification included dissection of interior rims, emplacement of depositional aprons with basinward scarps, remnant glaciers and associated fresh shallow valleys, supraglacial debris, and candidate moraines. On crater exterior rims and on the plateaus surrounding Batson crater we describe moderate incision and sedimentation, subglacial meltwater runoff through Navua A Valles, candidate eskers, valleys discordant with topography but concordant with inferred ice flow direction, and hummocky material, among others. Wet-based glaciation and subglacial runoff may have been favored due to a locally enhanced geothermal heating or strain heating on steep crater slopes. This work presents a comprehensive and detailed characterization of landforms interpreted as glacial in origin, which could be used to guide identifications of glacial landforms in other cratered regions of Mars.

Slopes of Lunar Crater Size‐Frequency Distributions at Copernican‐Aged Craters

AbstractCraters on the lunar surface can provide valuable information about the timing and sequence of surface‐forming processes on the Moon. A commonly used method for age determination is the analysis of the crater size‐frequency distribution (CSFD) to which a production function (PF) is fitted that represents the size‐frequency distribution of the impactors. However, the commonly used PF of Neukum (1983) is valid for crater diameters between 10 m and 300 km. Neukum et al. (2001, https://doi.org/10.1007/978-94-017-1035-0_3) revised the PF for crater diameters of 100 m–200 km. However, it is suggested to also be valid for the diameter range of 10 m–300 km as well. To assess whether we can extend a PF to craters ≤10 m in diameter, we investigated the slopes of the CSFDs of small craters formed on ejecta of young Copernican‐aged craters Giordano Bruno, Moore F, North Ray, and South Ray. A PF for smaller diameters would allow dating of young geological units, which are typically small, and would reduce the statistical error in age determinations, since smaller craters are more abundant. However, small craters are strongly influenced by geological factors, such as target properties, crater degradation, and secondary craters. For craters between 10 and 20 m we obtain a steeper CSFD slope than Neukum's proposed −3 slope (cumulative), whereas for craters ≤10 m the slope is about −3. We conclude that the PF of Neukum (1983) provides a reasonable CSFD slope for smaller craters, although it was not developed for this crater diameter range.

Subsurface pulse, crater and ejecta asymmetry from oblique impacts into granular media

We carry out experiments of 104 m/s velocity oblique impacts into a granular medium (sand). Impact craters have nearly round rims even at a grazing angle of about 10°, however, the strength of seismic pulses excited by the impact is dependent upon impact angle, and the ratio between uprange and downrange velocity peaks can be as large as 5, particularly at shallow depths. Crater slope, an offset between crater center and impact site, crater volume, azimuthal variation in ejection angle, seismic pulse shapes and subsurface flow direction are also sensitive to impact angle, but to a much lower degree than subsurface pulse strength. Uprange and downrange pulse peak amplitudes can be estimated from the horizontal and vertical components of the momentum imparted to the medium from the projectile.

Morphological characteristics of impact craters with diameters of 5–20 km on the Moon

The morphology of impact craters on the Moon plays an important role in understanding impact cratering process, surface and subsurface properties, and their evolutions. In this study, we systematically analyzed the depth, rim height, slope, and rock abundance of 15,135 impact craters between 5 and 20 km in diameter on the Moon, covering the simple and simple-to-complex transitional crater regimes. We found that the decline rates of inner average slopes of mare craters are generally larger than those of non-maria craters and that the degradation rate of inner upper wall slopes around rim crest is not uniform, which decreases rapidly when the depth/diameter ratio (d/D) lies in 0.25–0.15 but slowly when d/D is in 0.15–0.05. However, we found that there is no difference in crater rim height between different terrains (e.g., maria and highlands). In addition, we also found the decrease in rock abundance is more rapid than the ejecta infilling of the crater floor, especially for large simple craters. Moreover, we investigated the diameter-dependent morphological features of fresh craters in different terrains and revised the onset of transitional crater diameters based on the 180 freshest craters. We found that crater initial depth depends on target properties (e.g., strength and porosity) whereas that the degradation rate of the crater depth is independent of terrains. Furthermore, we found that the power-law relations for depth and diameter of fresh simple craters are d = 0.293D0.865 (mare), d = 0.297D0.884 (highland), d = 0.221D0.959 (north pole) and d = 0.209D0.981 (south pole). The onsets of transitional crater diameters are ∼14.2 km (mare), ∼15.7 km (highland), ∼16.6 km (north pole), and ∼ 16.8 km (south pole). These morphological characteristics and their differences in different terrains suggest that target properties (e.g., strength, layering, and porosity) affect the formation and degradation of larger simple and transitional craters.

Long‐Lived and Continual Volcanic Eruptions, Tectonic Activity, Pit Chains Formation, and Boulder Avalanches in Northern Tharsis Region: Implications for Late Amazonian Geodynamics and Seismo‐Tectonic Processes on Mars

AbstractTharsis is the largest volcanic province on Mars. It consists of a few large shield volcanoes, one of which is Alba Mons (AM), located in northern Tharsis, with the Ceraunius Fossae (CF) graben system to the south of it. Previous workers argued in favor of episodic building of Tharsis volcanoes. In contrast, we show that volcanism in the AM and CF regions occurred continually, at least in the last few hundred million years, based on ages of >1,000 stratigraphically young lava flows. Central volcanism in AM terminated around 200 Ma, while subsequent young volcanism, fed by both small shields and fissures, migrated to the south in CF. Several generations of grabens hosting thousands of simple to complex pit chains were formed by magmatic intrusion through feeder dikes, and these activities also migrated to the south during the Late Amazonian epoch. Thousands of boulder avalanches mark the slopes of grabens, pit chains, and impact craters, with ages ranging from a few tens to thousands of years. The local geological settings of the boulder falls suggest that both tectonic and volcanic marsquakes triggered the boulder avalanches. The broad zone of boulder falls in northern Tharsis defines the potential epicentral zone of (MW 4.1) 18 September 2021 marsquake. We infer that long‐lived and active magma chambers and subcrustal magma underplating driven by a mantle plume are present beneath the AM volcano and that these probably migrated south toward CF in the Late Amazonian epoch.

Topographic Degradation Processes of Lunar Crater Walls Inferred From Boulder Falls

AbstractRecent explorations by lunar orbiters have shown that boulder falls are distributed over the entire lunar surface. To quantitatively evaluate the effects of moonquakes and meteorite impacts on boulder falls, we performed detailed surveys at two sites: One in the southern part of the Schrödinger basin (Site 1) and the other in Laue crater (Site 2). Using images and topography data from the Lunar Reconnaissance Orbiter and KAGUYA, we measured the detailed distributions of boulder falls, small craters, slope angles, and the optical maturity parameter (OMAT) and modeled maximum ground acceleration due to impacts at these sites. In steeply sloping areas at both sites, we found that the density of small craters was low and areas with high OMAT values corresponded to boulder sources, where many boulders exist. At Site 1, the starting points of boulder falls and ground acceleration due to impacts were correlated. In addition, craters with boulder falls at and around Site 2 were distributed independently of the presumable epicentral distance from a shallow moonquake that occurred in 1975 near Site 2, which was previously inferred to have triggered boulder falls at the site. Our results suggest that boulder falls at these sites were triggered not by moonquakes but by meteorite impacts. We propose a model for the generation and transport of boulders and regolith on slopes by meteorite impacts, which may be directly related to the degradation of crater slopes on the Moon.

An Insight Into Ancient Aeolian Processes and Post‐Noachian Aqueous Alteration in Gale Crater, Mars, Using ChemCam Geochemical Data From the Greenheugh Capping Unit

AbstractAeolian processes have shaped and contributed to the geological record in Gale crater, Mars, long after the fluviolacustrine system existed ∼3 Ga ago. Understanding these aeolian deposits, particularly those which have been lithified and show evidence for aqueous alteration, can help to constrain the environment at their time of deposition and the role of liquid water later in Mars' history. The NASA Curiosity rover investigated a prominent outcrop of aeolian sandstone within the Stimson formation at the Greenheugh pediment as part of its investigation of the Glen Torridon area. In this study, we use geochemical data from ChemCam to constrain the effects of aeolian sedimentary processes, sediment provenance, and diagenesis of the sandstone at the Greenheugh pediment, comparing the Greenheugh data to the results from previous Stimson localities situated 2.5 km north and >200 m lower in elevation. Our results, supported by mineralogical data from CheMin, show that the Stimson formation at the Greenheugh pediment was predominately sourced from an olivine‐rich unit that may be present farther up the slopes of Gale crater's central mound. Our results also suggest that the Greenheugh pediment Stimson formation was cemented by surface water runoff such as that which may have formed Gediz Vallis. The lack of alteration features in the Stimson formation at the Greenheugh pediment relative to those of the Emerson and Naukluft plateaus suggests that groundwater was not as available at this locality compared to the others. However, all sites share diagenesis at the unconformity.

Karst Ecosystems of Middle Timan, Russia: Soils, Plant Communities, and Soil Oribatid Mites

Oribatid mites are distinguished by high taxonomic diversity and abundance in almost all natural zones; they are used as an indicator group of microarthropods in the study of natural landscapes and anthropogenically disturbed ecosystems. In the karst landscapes of the North, the oribatid mites are very poorly studied. The aim of this study was to investigate the diversity of soil types, plant communities, and oribatid mites in karst relief forms in the conditions of the northern taiga forests. The material was collected in July 2020 in the karst landscapes of Timan Ridge, found in the European northeast of Russia. The research sites were located in the profile of the karst crater and in the profile of the slope in the Ukhta River Valley. A sedge wetland community, and pine–bilberry–green-moss forest, located in the depression between glacial hills and uplands were also examined. A total of seven sites were examined. Geobotanical descriptions were made by standard methods, descriptions of the soil profile, and samples of the soil microfauna; 12 in each site were collected. A total of 51 oribatid mite species from 39 genera and 31 families were found. The highest taxonomic diversity of oribatids was noted in forest phytocenoses located in the upper part of the karst crater slope, the lower part of the karst crater slope, and on rock outcrops in the lower part of the slope in Ukhta river valley. Ordination of the oribatid mite community by NMDS method showed the association of sites S3, S4, and S5 located on the slope of the karst crater in one group, and sites S6 and S7 located on a slope in the Ukhta River Valley, as well as S2 (pine–bilberry–green-moss forest located in the depression between glacial hills and uplands), in another group. The swamp community was located separately from other communities. Species of oribatid mites, which created the specifics of each community, were noted. The specifics of the population of oribatid mites of karst landscapes were that along with the features of fauna, characteristic for zonal north-taiga forests (the predominance of polyzonal widespread species) were found the “conditionally southern” species, the main area of distribution of which is located in lower latitudes. The study provides the basis for future studies of poorly known oribatid mites of karst landscapes of Northern Europe.

Insights into the subsurface structure of wrinkle ridges on Mars

Wrinkle ridges are important landforms on Mars and other planetary bodies and result from horizontal tectonic shortening. This study provides insights into the subsurface of selected wrinkle ridge sites, based on exposures provided by steep escarpments and crater slopes that crosscut wrinkle ridges. We mapped the complex fold and fault patterns and measured fault dips, where faults appear planar. The fault pattern underneath wrinkle ridges is diverse and is dominated by reverse faults and thrusts. The predominance of one fault system leads to morphological asymmetries of many wrinkle ridges. The upper tip of the dominant thrust fault is commonly situated beneath the steeper wrinkle ridge slope and may outcrop at its base. Polarity changes of wrinkle ridges along strike go along with a change of the dominant thrust direction. Symmetric wrinkle ridges are formed when a conjugate system of thrusts exists in the subsurface. Several wrinkle ridges display a main thrust fault whose dip angle bends over to a shallower dip at depth. The measurements of average dip for primary thrust and backthrust faults are 37° ± 2° and 28 ± 2°, respectively. In general, most of the examined wrinkle ridges are characterized by a multitude of subsidiary and backthrust faults. With the limitation that the uppermost 500-1000 m of the wrinkle ridges subsurface are accessible in this study and despite the large morphological and structural variability of wrinkle ridges, the kinematics of fault-propagation folds models seem to show a large match to our observations and measurements. Likewise, continuum mechanics models show a good fit to the obtained structural data. Fault-bend fold models and simple buckle folding models seem less compatible with observations.

Reconstructing East African monsoon variability from grain-size distributions: End-member modeling and source attribution of diatom-rich sediments from Lake Chala

Grain-size analysis and end-member modeling of the clastic fraction of the 25-kyr sediment sequence from Lake Chala, a meromictic crater lake on the lower east slope of Mt. Kilimanjaro, reveal crucial aspects of climate-driven environmental change in equatorial East Africa since the Last Glacial Maximum. The finely laminated sediments of Lake Chala contain only up to 40% of clastic components, the rest are mainly diatom frustules and amorphous organic matter. Measured grain-size distributions were split into six statistically meaningful end members, of which four could be linked to a distinct source and transport mechanism of clastic mineral input: fine aeolian dust from distal sources (EM1), fine catchment runoff (EM2), coarser aeolian dust from proximal sources (EM5) and coarse erosive material from the upper crater slopes (EM6). The two other end members (EM3 and EM4) represented frustules of the two most common diatom taxa in Lake Chala, Afrocymbella barkeri and Nitzschia fabiennejansseniana, which had (partly) survived sample pre-treatment.Temporal variation in normalized abundance of the two dust-derived end members are valuable proxies for past changes in monsoon circulation over equatorial East Africa. During Northern Hemisphere cold periods (e.g., Last Glacial Maximum and Younger Dryas) the Inter-Tropical Convergence Zone shifted southward, enhancing northeasterly monsoon winds in the Lake Chala area and increasing advection of fine dust from the dry Horn of Africa region. Simultaneously, more modest continental heating reduced the prevalence of small-scale atmospheric turbulence, and thus the occurrence of dust devils, resulting in reduced influx of coarse dust from drylands nearby. Conversely, abrupt intensification of the southeasterly monsoon at the onset of the Holocene is recorded by an abrupt increase in the amount of coarse dust delivered to Lake Chala. Temporal variation in the end members representing catchment run-off (EM2) and erosion (EM6) mainly reflect changes in lacustrine sedimentation dynamics associated with major lake-level fluctuation, as evidenced by other paleoenvironmental proxies. Overall this study shows that subdivision of the clastic fraction of lacustrine sediments into statistically robust grain-size end members can provide multiple independent and quantitative proxies which help constrain reconstructions of a region’s multi-faceted climate history.

Geomorphology, morphometry, spatial distribution and ages of mafic monogenetic volcanoes of the Peinado and Incahuasi fields, southernmost Central Volcanic Zone of the Andes

The back-arc southern Puna region (south of ~24°S) in the Central Volcanic Zone of the Andes contains hundreds of Miocene to Quaternary mafic monogenetic volcanoes roughly distributed in several volcanic fields. Analysis of the geomorphology, morphometry, spatial distribution and age of 36 mafic monogenetic centers in the Peinado and Incahuasi fields, at the southwestern margin of the Puna plateau, gives insights on the links that mafic monogenetic volcanism can have with main and secondary structures, and the effects of degradation on scoria cone shape. Degree of preservation, morphometry and six new unspiked K-Ar ages indicate two distinct age groups, old centers > 2 Ma and young centers ≤ 1 Ma. The older mafic centers consist of degraded scoria cones and lava flows with an estimated cumulative bulk volume of 2.2 km3. The younger mafic centers display a variety of well-preserved landforms (scoria cones, lava flows, maars, tuff rings, domes) and have an estimated cumulative volume of 6.2 km3. Their distribution in a main NNE-SSW and secondary ENE-WSW trends suggests a control by the regional NNE-SSW striking Peinado and San Francisco fault systems in a dextral strike-slip configuration. Scoria cone and lava flow morphometries are similar in both fields, but a marked difference indicating hydrovolcanic activity is the presence of tuff rings, maars and tephra fallout deposits only in the Peinado field. Morphometric analysis of dated pristine and degraded scoria cones of the southern Puna region shows that parameters related to crater depth and inner crater steepness decrease consistently with age, suggesting that crater infilling is the degradation-related process that is most sensitive to age at scoria cones. In the southern Puna, high values of crater depth/crater width, crater depth/cone height and mean inner crater slope are indicative of a young (<1 Ma) age, but low values are not necessarily indicative of an old (>1 Ma) age, as young cones can have initially low values.

Evidence for thermal-stress-induced rockfalls on Mars impact crater slopes

Here we study rocks falling from exposed outcrops of bedrock, which have left tracks on the slope over which they have bounced and/or rolled, in fresh impact craters (1–10 km in diameter) on Mars. The presence of these tracks shows that these rocks have fallen relatively recently because aeolian processes are known to infill topographic lows over time. Mapping of rockfall tracks indicate trends in frequency with orientation, which in turn depend on the latitudinal position of the crater. Craters in the equatorial belt (between 15°N and 15°S) exhibit higher frequencies of rockfall on their north-south oriented slopes compared to their east-west ones. Craters >15° N/S have notably higher frequencies on their equator-facing slopes as opposed to the other orientations. We computed solar radiation on the surface of crater slopes to compare insolation patterns with the spatial distribution of rockfalls, and found statistically significant correlations between maximum diurnal insolation and rockfall frequency. Our results indicate that solar-induced thermal stress plays a more important role under relatively recent climate conditions in rock breakdown and preconditioning slopes for rockfalls than phase transitions of H2O or CO2, at mid- and equatorial-latitudes. Thermal stress should thus be considered as an important factor in promoting mass-wasting process on impact crater walls and other steep slopes on Mars.

Melt-water formed dark streaks on slopes of Haughton crater as possible Mars analogues

AbstractHaughton crater in the Canadian Arctic has been extensively used as a Mars (and lunar) analogue over the past 20 years. Here we report on small scale, dark, semi-seasonal slope streaks formed by melt water flowing down the crater walls that we observed during the Mars Society-sponsored M160 expedition to the F-MARS facility on the NW rim of the crater. The streaks are formed by biofilms colonizing snow melt flowing from semi-permanent snow patches in Haughton crater on Devon Island and elsewhere in the Canadian Arctic. These features superficially resemble the dark slope streaks and recurring slope lineae (RSL) observed on Mars and may serve as analogues for wet models for their formation and a contrast with dry formation models. Their significance to astrobiology and planetary science is three-fold: (1) as examples of dark recurring streaks known to be associated with water they provide a benchmark to compare with Martian slope streaks and RSL. (2) The melt streaks may have potential as astrobiological analogues for wet models of slope streaks and RSL. (3) They are natural laboratories to study planetary protection issues associated with robotic and astronaut exploration of potential water-related slope features on Mars.

Mars Climate History: Insights From Impact Crater Wall Slope Statistics

AbstractWe use the global distribution of the steepest slopes on crater walls derived from Mars Orbiter Laser Altimeter profile data to assess the magnitudes of degradational processes with latitude, altitude, and time. We independently confirm that Amazonian polar/high‐latitude crater slope modification is substantial, but that craters in the low latitudes have essentially escaped significant slope modification since the Early Hesperian. We find that the total amount of crater wall degradation in the Late Noachian is very small in comparison to the circumpolar regions in the Late Amazonian, an observation that we interpret to mean that the Late Noachian climate was not characterized by persistent and continuous warm and wet conditions. A confirmed elevational zonality in degradation in the Early Hesperian is interpreted to mean that the atmosphere was denser than today.

Gullies and debris-flows in Ladakh Himalaya, India: a potential Martian analogue

Abstract We conducted comparative morphological analysis of gullies within two high-latitude Martian craters (Domoni and Maricourt) in the northern hemisphere of Mars with (1) the debris-flow gully systems in the Ladakh Himalaya and (2) Istok Crater in the southern mid-latitudes of Mars where water-bearing debris-flow deposits have been previously reported. Our findings suggest that the debris-flow landforms preserved on gully and alluvial fans in the Ladakh Himalaya are potential analogues for the deposits preserved over the equator-facing slopes of Domoni and Maricourt Craters. Further, we found that the morphological attributes of channels and deposits (including overlapping terminal lobes, levées, tongue-shaped/lobate deposits and broad/small depositional deposits) within both the study craters and Istok Crater are similar. As a result, the studied craters emerge as additional sites in which possible evidence of water-bearing debris-flows are preserved on Mars. By comparison to our Earth analogue, we further propose that episodic melting of snow accumulated within the sheltered alcoves is the most likely source of water for the formation of such gullies. Taken together, our findings suggest that debris-flow may not be a rare process in gully formation on Mars and evidence may be preserved in other unexplored areas.

Relationship between Diffuse CO2 Degassing and Volcanic Activity. Case Study of the Poás, Irazú, and Turrialba Volcanoes, Costa Rica

Active volcanoes exhibit diffuse gas emanations through the ground, the most abundant species of which is CO2. However, the relationship between diffuse degassing and volcanic activity is not often clear and some volcanoes may have low diffuse degassing levels despite having strong volcanic activity. The main goals of this study are to quantify diffuse CO2 degassing and determine whether patterns exist in relation to volcanic activity through the study of Turrialba, Poas and Irazu, three active volcanoes in Costa Rica which are at different stages of activity. Structural controls of spatial distribution of diffuse degassing were also investigated. Measurement campaigns were conducted using the accumulation chamber method coupled with 10 cm depth ground temperature sampling with the aim of estimating the total diffuse CO2 degassing budget. The total amount of CO2 emitted diffusely by each volcano is approximately 113 ± 46 t/d over ~ 0.705 km2 for Turrialba, 0.9 ± 0.5 t/d for Poas over ~ 0.734 km2, 3.8 ± 0.9 t/d over ~ 0.049 km2 for Irazu's main crater, and 15 ± 12 t/d over 0.0059 km2 for Irazu's north flank. Turrialba and Poas volcano diffuse degassing budget represent about 10\% of the whole gas output. Both volcanoes were in a transitional stage and the opening of new conduits may cause a loss in diffuse degassing and an increase of active degassing. Numerous diffuse degassing structures were also identified. One of which at Turrialba was closely associated with the collapse of a crater wall in 2014 during the initiation of a new period of heightened eruptive activity. Similar structures were also observed on the outer slopes of the west crater, suggesting strong alteration and perhaps destabilization of the upper outer cone. Irazu's north flank is highly permeable and has experienced intense hydrothermal alteration.

Modeling concentric crater fill in Utopia Planitia, Mars, with an ice flow line model

Impact craters in the mid-latitudes of Mars are commonly filled to variable degrees with some combination of ice, dust, and rocky debris. Concentric surface features visible in these craters have been linked to debris transportation and glacial and periglacial processes. Concentric crater fill (CCF) observed today are interpreted to be the remains of repeated periods of accumulation and sublimation during the last tens to hundreds of million years. Previous work suggests that during phases of high obliquity, ice accumulates in crater interiors and begins to flow down steep crater slopes, slowly filling the crater. During times of low obliquity ice is protected from sublimation through a surface debris layer consisting of dust and rocky material. Here, we use an ice flow line model to understand the development of concentric crater fill.In a regional study of Utopia Planitia craters, we address questions about the influence of crater size on the CCF formation process, the time scales needed to fill an impact crater with ice, and explore commonly described flow features of CCF. We show that observed surface debris deposits as well as asymmetric flow features can be reproduced with the model. Using surface mass balance data from global climate models and a credible obliquity scenario, we find that craters less than 80 km in diameter can be entirely filled in less than 8 My, beginning as recently as 40 Ma ago. Uncertainties in input variables related to ice viscosity do not change the overall behavior of ice flow and the filling process. We model CCF for the Utopia Planitia region and find subtle trends for crater size versus fill level, crater size versus sublimation reduction by the surface debris layer, and crater floor elevation versus fill level.

Morphometric analysis of scoria cones: the potential for inferring process from shape

Abstract Geometric analysis was used to define seven morphometric parameters for the description of the shape of scoria cones, including volume, orientation and five shape parameters (flat-topped-ness, steep-sided-ness, relative crater depth, crater slope and elongation). The measurement and analysis of these shape factors for five distinct scoria cone populations facilitated an exploration of the overlapping effects of growth and erosion processes on shape. Flat-topped-ness seemed to be insensitive to either growth or erosion, suggesting a dependence on eruption energetics. Most of the variation in steep-sided-ness originated from eruptions ending during variable (early to mature) stages of development (growth) and from erosional processes, although steep-sided-ness was also sensitive to eruption energetics (through fragmentation and its impact on the angle of repose). Steep-sided-ness was therefore a poor indicator of geomorphic age. Distinct types of scoria cone shape (ideal, gully, horseshoe, tilted, crater row, parasitic and amorphous) captured a variety of deviations in shape from the purely conical, yet the conical shape parameters differed little in average value between the shape types. The conical shape parameters captured the growth and erosion processes (e.g. ballistic delivery, tephra redistribution via avalanching and erosional transport) common to all scoria cones rather than the particular processes that made the shape types unique (e.g. breaching, rafting and wind effects). Supplementary material: Locations of examples of the shape types are available at https://doi.org/10.6084/m9.figshare.c.3661907

Spatial-temporal distribution of the black rhino population in the Ngorongoro Crater, Tanzania

Ngorongoro Conservation Area (NCA) is vital especially for black rhino conservation because it is one of the only two ecosystems in Tanzania that host native black rhino populations. However, the spatial-temporal distribution of rhinos in this ecosystem have not been assessed. The purpose of this study was to assess the temporal and spatial distribution of rhinos and factors responsible for the uneven seasonal distribution. The study was conducted in Ngorongoro Conservation Area (NCA) which is located at 3°12′S, 35°27′E during the wet (May-June 2015) and dry (August-September 2015) sampling periods. Road drives were conducted daily for a period of one month during each season to map the spatial distribution of the black rhino, and assess the relative abundance of its forage resources and diet selection. During each drive, the roadsides were inspected for the presence of rhinos, with stops being made each time an individual or group of rhinos is located. Results shows that the distribution patterns of the black rhino differed markedly between wet and dry sampling periods. During the dry period, rhinos were mainly concentrated in the crater slopes dominated by shrubby vegetation, swamps and along riverine areas of the crater. During wet season in there were more herbage material mostly preferred by black rhino in crater floor as most rhinos were sighted in these sampling areas. Human activities such as tourism infrastructure (lodges, campsites and roads) should be kept minimal to minimize disruption to rhino movement and habitat selection patterns and buffer zones be established within crater-community interfaces where human activities such as livestock grazing are strictly prohibited to ensure natural distribution ranges are maintained.

The meteorology of Gale Crater as determined from Rover Environmental Monitoring Station observations and numerical modeling. Part II: Interpretation

Numerical modeling results from the Mars Regional Atmospheric Modeling System are used to interpret the landed meteorological data from the Rover Environmental Monitoring Station onboard the Mars Science Laboratory rover Curiosity. In order to characterize seasonal changes throughout the Martian year, simulations are conducted at Ls 0, 90, 180 and 270. Two additional simulations at Ls 225 and 315 are explored to better understand the unique meteorological setting centered on Ls 270. The synergistic combination of model and observations reveals a complex meteorological environment within the crater. Seasonal planetary circulations, the thermal tide, slope flows along the topographic dichotomy, mesoscale waves, slope flows along the crater slopes and Mt. Sharp, and turbulent motions all interact in nonlinear ways to produce the observed weather. Ls 270 is shown to be an anomalous season when air within and outside the crater is well mixed by strong, flushing northerly flow and large amplitude, breaking mountain waves. At other seasons, the air in the crater is more isolated from the surrounding environment. The potential impact of the partially isolated crater air mass on the dust, water, noncondensable and methane cycles is also considered. In contrast to previous studies, the large amplitude diurnal pressure signal is attributed primarily to necessary hydrostatic adjustments associated with topography of different elevations, with contributions of less than 25% to the diurnal amplitude from the crater circulation itself. The crater circulation is shown to induce a suppressed boundary layer.