Gasa impact crater,Mars: Very young gullies formed from impact into latitude-dependent mantle and debris-covered glacier deposits?     

Samuel C. Schon  James W. Head 《Icarus》2012,218(1):459-477

The mode of formation of gullies on Mars, very young erosional–depositional landforms consisting of an alcove, channel, and fan, is one of the most enigmatic problems in martian geomorphology. Major questions center on their ages, geographic and stratigraphic associations, relation to recent ice ages, and, if formed by flowing water, the sources of the water to cause the observed erosion/deposition. Gasa (35.72°S, 129.45°E), a very fresh 7-km diameter impact crater and its environment, offer a unique opportunity to explore these questions. We show that Gasa crater formed during the most recent glacial epoch (2.1–0.4 Ma), producing secondary crater clusters on top of the latitude-dependent mantle (LDM), interpreted to be a layered ice-dust-rich deposit emplaced during this glacial epoch. High-resolution images of a pre-Gasa impact crater ～100 km northeast of Gasa reveal that portions of the secondary-crater-covered LDM have been removed from pole-facing slopes in crater interiors near Gasa; gullies are preferentially located in these areas and channels feeding alcoves and fans can be seen to emerge from the eroding LDM layers to produce multiple generations of channel incision and fan lobes. We interpret these data to mean that these gullies formed extremely recently in the post-Gasa-impact time-period by melting of the ice-rich LDM. Stratigraphic and topographic relationships are interpreted to mean that under favorable illumination geometry (steep pole-facing slopes) and insolation conditions, melting of the debris-covered ice-rich mantle took place in multiple stages, most likely related to variations in spin-axis/orbital conditions. Closer to Gasa, in the interior of the ～18 km diameter LDM-covered host crater in which Gasa formed, the pole-facing slopes display two generations of gullies. Early, somewhat degraded gullies, have been modified by proximity to Gasa ejecta emplacement, and later, fresh appearing gullies are clearly superposed, cross-cut the earlier phase, and show multiple channels and fans, interpreted to be derived from continued melting of the LDM on steep pole-facing slopes. Thus, we conclude that melting of the ice-rich LDM is a major source of gully activity both pre-Gasa crater and post-Gasa crater formation. The lack of obscuration of Gasa secondary clusters formed on top of the LDM is interpreted to mean that the Gasa impact occurred following emplacement of the last significant LDM layers at these low latitudes, and thus near the end of the ice ages. This interpretation is corroborated by the lack of LDM within Gasa. However, Gasa crater contains a robustly developed set of gullies on its steep, pole-facing slopes, unlike other very young post-LDM craters in the region. How can the gullies inside Gasa form in the absence of an ice-rich LDM that is interpreted to be the source of water for the other adjacent and partly contemporaneous gullies? Analysis of the interior (floor and walls) of the host crater suggest that prior to the Gasa impact, the pole-facing walls and floor were occupied by remnant debris-covered glaciers formed earlier in the Amazonian, which are relatively common in crater interiors in this latitude band. We suggest that the Gasa impact cratering event penetrated into the southern portion of this debris-covered glacier, emplaced ejecta on top of the debris layer covering the ice, and caused extensive melting of the buried ice and flow of water and debris slurries on the host crater floor. Inside Gasa, the impact crater rim crest and wall intersected the debris-covered glacier deposits around the northern, pole-facing part of the Gasa interior. We interpret this exposure of ice-rich debris-covered glacial material in the crater wall to be the source of meltwater that formed the very well-developed gullies along the northern, pole-facing slopes of Gasa crater.  相似文献   

Physical constraints on impact melt properties from Lunar Reconnaissance Orbiter Camera images     

Brett W. Denevi  Steven D. Koeber  Mark S. Robinson  W. Brent Garry  B. Ray Hawke  Thanh N. Tran  Samuel J. Lawrence  Laszlo P. Keszthelyi  Olivier S. Barnouin  Carolyn M. Ernst  Livio L. Tornabene 《Icarus》2012,219(2):665-675

Impact melt flows exterior to Copernican-age craters are observed in high spatial resolution (0.5 m/pixel) images acquired by the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). Impact melt is mapped in detail around 15 craters ranging in diameter from 2.4 to 32.5 km. This survey supports previous observations suggesting melt flows often occur at craters whose shape is influenced by topographic variation at the pre-impact site. Impact melt flows are observed around craters as small as 2.4 km in diameter, and preliminary estimates of melt volume suggest melt production at small craters can significantly exceed model predictions. Digital terrain models produced from targeted NAC stereo images are used to examine the three-dimensional properties of flow features and emplacement setting, enabling physical modeling of flow parameters. Qualitative and quantitative observations are consistent with low-viscosity melts heated above their liquidii (superheated) with limited amounts of entrained solids.  相似文献   

Evaluation of Simulated CO_2 Concentrations from the CarbonTracker-Asia Model Using In-situ Observations over East Asia for 2009–2013     

Samuel Takele KENEA  Young-Suk OH  Jae-Sang RHEE  Tae-Young GOO  Young-Hwa BYUN  Shanlan LI  Lev D.LABZOVSKII  Haeyoung LEE  Robert F.BANKS 《大气科学进展》2019,36(6):603-613

The CarbonTracker(CT) model has been used in previous studies for understanding and predicting the sources, sinks, and dynamics that govern the distribution of atmospheric CO_2 at varying ranges of spatial and temporal scales. However, there are still challenges for reproducing accurate model-simulated CO_2 concentrations close to the surface, typically associated with high spatial heterogeneity and land cover. In the present study, we evaluated the performance of nested-grid CT model simulations of CO_2 based on the CT2016 version through comparison with in-situ observations over East Asia covering the period 2009–13. We selected sites located in coastal, remote, inland, and mountain areas. The results are presented at diurnal and seasonal time periods. At target stations, model agreement with in-situ observations was varied in capturing the diurnal cycle. Overall, biases were less than 6.3 ppm on an all-hourly mean basis, and this was further reduced to a maximum of 4.6 ppm when considering only the daytime. For instance, at Anmyeondo, a small bias was obtained in winter, on the order of 0.2 ppm. The model revealed a diurnal amplitude of CO_2 that was nearly flat in winter at Gosan and Anmyeondo stations, while slightly overestimated in the summertime. The model's performance in reproducing the diurnal cycle remains a challenge and requires improvement. The model showed better agreement with the observations in capturing the seasonal variations of CO_2 during daytime at most sites, with a correlation coefficient ranging from 0.70 to 0.99. Also, model biases were within-0.3 and 1.3 ppm, except for inland stations(7.7 ppm).  相似文献   

Capability of LISEM to estimate flood hydrographs in a watershed with predominance of long-duration rainfall events     

Vargas  Marcelle Martins  Beskow  Samuel  de Mello  Carlos Rogério  de Moura  Maíra Martim  Nunes  Maria Cândida Moitinho  Faria  Lessandro Coll  Aquino  Leandro Sanzi 《Natural Hazards》2021,109(1):593-614

Natural Hazards - Process-based hydrological models are of great importance to understand hydrological processes and support decision making. The LImburg Soil Erosion Model (LISEM) requires...  相似文献   

An apatite U-Pb thermal history map for the northern Gawler Craton,South Australia     

James W.Hall  Stijn Glorie  Anthony J.Reid  Samuel C.Boone  Alan S.Collins  ANDrew Gleadow 《地学前缘(英文版)》2018,9(5):1293-1308

Apatite U-Pb thermochronology was applied to granitoid basement samples across the northern Gawler Craton to unravel the Proterozoic, post-orogenic, cooling history and to examine the role of major fault zones during cooling. Our observations indicate that cooling following the ~2500 Ma Sleaford Orogeny and ~1700 Ma Kimban Orogeny is restricted to the Christie and Wilgena Domains of the central northern Gawler Craton. The northern Gawler Craton mainly records post-Hiltaba Event(~1590 Ma) U-Pb cooling ages. Cooling following the ~1560 Ma Kararan Orogeny is preserved within the Coober Pedy Ridge,Nawa Domain and along major shear zones within the south-western Fowler Domain. The Nawa Domain samples preserve U-Pb cooling ages that are 150 Ma younger than the samples within the Coober Pedy Ridge and Fowler Domain, indicating that later(~1300 Ma) fault movement within the Nawa Domain facilitated cooling of these samples, caused by arc collision in the Madura Province of eastern Western Australia. When compared to~(40)Ar/~(39) Ar from muscovite, biotite and hornblende, our new apatite U-Pb ages correlate well, particularly in regions of higher data density. Our data also preserve a progressive younging of U-Pb ages from the nucleus of the craton to the periphery with a stark contrast in U-Pb ages across major structures such as the Karari Shear Zone and the Southern Overthrust, which indicates the timing of reactivation of these major crustal structures. Although this interpolation was based solely on thermochronological data and did not take into account structural or other geological data, these maps are consistent with the structural architecture of the Gawler Craton and reveal the thermal footprint of known tectonic and magmatic events in the Gawler Craton.  相似文献   

Field report: Sailing around the exhumed roots of the Mesozoic Patagonian paleo-accretionary wedge(Diego de Almagro Island,Chile)     

Samuel Angiboust  Jesus Mu?oz 《地学前缘(英文版)》2018,9(5):1591-1594

We undertook a boat expedition to explore the geological framework of a very remote, lesser-known island, in the Chilean Patagonia: the Diego de Almagro Island(latitude S51°330'). This uninhabited, ca.400 km~2 Island is one of the very rare exposures of the Mesozoic accretionary subduction complex along the Chilean margin. Unstable weather, strong winds, steep topography, and very dense vegetation make an on-land mission difficult. Careful preparation based on high-resolution satellite images is advised to optimize shore access and minimize risks of injury. Despite a relatively important degree of regional reequilibration of metamorphic assemblages due to sluggish exhumation through the forearc crust, our results have shown that the island is composed of a nappe stack of ocean-floor derived slivers of metasedimentary units that exhibit very different pressure-temperature-time paths during burial by subduction under the Chilean margin and subsequent exhumation. These rocks are witness to a complex thermal evolution of the subduction zone between Jurassic and Cretaceous times from granulite facies to blueschist facies conditions as well as multiple episodes of accretion at ca. 35 -40 km in depth for almost100 Ma over the Mesozoic era.  相似文献   

UD-SV: Urban data services and visualization framework for sharing multidisciplinary research     

John Samuel  Vincent Jaillot  Clément Colin  Diego Vinasco Alvarez  Eric Boix  Sylvie Servigne  Gilles Gesquière 《Transactions in GIS》2023,27(3):841-858

With the widespread availability of a large volume of urban data, stakeholders from different domains require advanced tools to manage, visualize and understand cities and their evolution. During the last few years, researchers have proposed numerous research works and applications to illustrate the cities of the past and possible scenarios of the future under different conditions. However, many of these approaches are one-time solutions and not based on standards, making them obsolete and unusable for reproducible research. In this article, we present UD-SV: an Urban data-Services and Visualization open-source framework for multidisciplinary research to handle complex processing, analysis, and visualization of urban data. However, our goal is not to present a one-time monolithic software solution for urban data management and analysis, but we demonstrate the design and development of an open and interoperable software framework driven by use cases from diverse users to solve applied research challenges. The main contribution of UD-SV is that it uses open standards and open data with documented and reproducible processes with a particular emphasis on the reuse of existing open-source software components. We also show an enhanced use of standards to enable a shift toward components that are interchangeable or composable with other existing components in the GIS community.  相似文献   

Accelerated climate change and its potential impact on Yak herding livelihoods in the eastern Tibetan plateau   总被引：1，自引：0，他引：1  

Michelle A. Haynes  King-Jau Samuel Kung  Jodi S. Brandt  Yang Yongping  Donald M. Waller 《Climatic change》2014,123(2):147-160

The Tibetan Plateau has experienced rapid warming like most other alpine regions. Regional assessments show rates of warming comparable with the arctic region and decreasing Asian summer monsoons. We used meteorological station daily precipitation and daily maximum and minimum temperature data from 80 stations in the eastern Tibetan Plateau of southwest China to calculate local variation in the rates and seasonality of change over the last half century (1960–2008). Daily low temperatures during the growing season have increased greatly over the last 24 years (1984–2008). In sites of markedly increased warming (e.g., Deqin, Yunnan and Mangya, Qinghai), daily and growing season daily high temperatures have increased at a rate above 5 °C/100 years. In Deqin, precipitation prior to the 1980s fell as snow whereas in recent decades it has shifted to rain during March and April. These shifts to early spring rains are likely to affect plant communities. Animals like yaks adapted to cold climates are also expected to show impacts with these rising temperatures. This region deserves further investigation to determine how these shifts in climate are affecting local biodiversity and livelihoods.  相似文献   

Are migrants exceptional resource degraders? A study of agricultural households in Ghana     

Samuel Nii Ardey Codjoe  Richard E. Bilsborrow 《GeoJournal》2012,77(5):681-694

Although some scholars describe migrant farmers as ‘exceptional resource degraders’ others do not. This paper uses evidence from the transitional agro-ecological zone of Ghana, to examine whether there are substantial differences between households of migrants and the host population regarding agricultural land use. The aim is to determine whether migrants are more destructive of the land (and hence the environment) than the host population. This will be examined using a standard model of the determinants of agricultural land use, to which we add variables representing demographic impacts, including in-migration. The data used are from a household survey undertaken in 2002 among 110 migrant and 142 host population farming households in central Ghana. Results are mixed. We find no support for the hypothesis that households with migrants are less likely to consider the long-term effects of land use by increasing the land area in cultivation, but at the same time there is evidence of use of more land-intensive agricultural practices which tend to degrade farm land over time.  相似文献   

Scenes from Avellaneda, Argentina     

Samuel R. Friedman 《GeoJournal》2012,77(4):451-451

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