All posts tagged Fan

The global distribution of alluvial fans on Mars

Post contributed by Dr Alex Morgan, Planetary Science Institute, USA

Alluvial fans are sedimentary deposits that form at the base of mountain fronts as a channel exits a steep, confined valley onto more gently sloped and unconfined terrain (Image 1). The channel loses its ability to transport sediment due to the reduction in slope and the lateral expansion of flow, and over time sediment is deposited into a semi-conical shape. The effects of water on a landscape are the most unambiguous markers of past climatic environment, and the distribution of alluvial fans provides a record of where and when liquid water was capable of transporting sediment on Mars in the past. Furthermore, as depositional features in close proximity with their sediment sources, alluvial fans preserve a record of environmental changes that occurred while sediment was being transported and deposited. In this study, we leveraged high resolution images from the CTX camera on Mars Reconnaissance Orbiter, which cover the entire surface of Mars, to conduct a global survey for fan-shaped sedimentary landforms across the martian surface and explore their implications for environmental change.

Image 1: A large alluvial fan in Harris crater, centered on 21.5°S, 67°E. The down-fan-trending ridges are interpreted to be paleochannels now in inverted relief due to preferential erosion of finer overbank deposits. This particular fan exhibits evidence for multiple episodes of sedimentation (Williams et al., 2011). CTX image G02_019160_1580_XN_22S292W.

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by fegbutcher on October 1, 2022  •  Permalink
Posted in Mars
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Posted by fegbutcher on October 1, 2022

https://planetarygeomorphology.wordpress.com/2022/10/01/the-global-distribution-of-alluvial-fans-on-mars/

Stepped Fans and Phyllosilicates on Mars

Post by Peter Grindrod, Natural History Museum, London, UK.

A number of different studies have catalogued features on Mars that could be given the general heading of sedimentary fans [e.g. Irwin et al., 2005; Kraal et al. 2008]. These features occur whenever the velocity of a river or stream decreases, and the water no longer has enough energy to carry its sediment, and thus begins to deposit its load. This drop in energy often occurs when the water flows into flatter and wider regions. The distribution of these fans on Mars is important because it shows the location of past water flows, and the amount of material that has been transported (which can be used as a proxy for flow duration).

However, one of the fundamental problems when looking at these features with orbital data alone, is that it is difficult to determine whether the river flowed into a standing body of water (for example a lake) or just an empty canyon or crater. Of course, the implications of this problem are important if we want to understand the volume and distribution of past water on Mars, which in themselves feed into understanding the past climate and even habitability of Mars.

Figure 1

Image 1: Location of the two fans in Coprates Catena, SE Valles Marineris. MOLA elevation overlain on THEMIS daytime image.

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by Tjalling de Haas on April 1, 2018  •  Permalink
Posted in Mars
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Posted by Tjalling de Haas on April 1, 2018

https://planetarygeomorphology.wordpress.com/2018/04/01/stepped-fans-and-phyllosilicates-on-mars/

The subsurface as the key to surface on Martian gullies

Post by Dr. T. de Haas, Department of Geography, Durham University.

Martian gullies are composite landforms that comprise an alcove, channel and depositional fan. They are very young geological features, some of which have been active over the last million years. Water-free sediment flows, likely triggered by CO2 sublimation, debris flows, and fluvial flows have all been hypothesized to have formed gullies. These processes require very different amounts of liquid water, and therefore their relative contribution to gully-formation is of key importance for climatic inferences. Formative inferences based on surface morphology may be biased however, because of substantial post-depositional modification (Images 1-3).

Image1

Image 1: Morphometry, morphology and stratigraphy of depositional landforms in Galap crater. (a) Overview and digital elevation model of Galap crater. (b) Detail of northwestern slope showing gradients of catchment and depositional fan. (c) Detail of proximal fan surface. (d) Detail of distal fan surface. (e) Detail of fan surface with incised channels; the dashed line indicates the rockfall limit. (f) Example of stratigraphic section. (h) Same stratigraphic section as in f, but with optimized contrast in the section. Arrows denote downslope direction. HiRISE image PSP_003939_1420.

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by suja82 on May 31, 2017  •  Permalink
Posted in Mars, Uncategorized
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Posted by suja82 on May 31, 2017

https://planetarygeomorphology.wordpress.com/2017/05/31/the-subsurface-as-the-key-to-surface-on-martian-gullies/

Sedimentology and Hydrology of an Amazonian paleo-fluivo-lacustrine systems on Mars (Moa Valles)

Post contributed by Francesco Salese from IRSPS/Dipartimento INGEO, Università D’Annunzio, Pescara, Italy.

Mars, is one of the planetary bodies where water flowed and where it may transiently flow today under certain conditions. Many martian paleodrainage systems and well-preserved fluvial and lacustrine deposits have been recognized and studied in the last two decades (see further reading). Widespread dendritic valley networks and the presence of extensive fluvial features on ancient martian terrains suggest that a relatively “warm and wet” climate was prevalent early in the planet’s history (about 3.7 Ga). This is in stark contrast with the hyper-arid, extremely cold climate that is thought to have persisted from 3 Ga until the present (Amazonian Era). The subject of this post is Moa Valles [Salese et al., 2016], which is a 2 billion year old paleodrainage system (Figure 1) that is nearly 300 km long and is carved into ancient highland terrains of Tempe Terra in the northern hemisphere of Mars. Understanding the origin and evolution of this type of complex and interconnected paleo-fluvio-lacustrine system is critical for understanding the early martian climate.

Figure2

Figure 1: The upper panel shows the THEMIS-VIS daytime mosaic of Moa Vallis system.The lower panel is a line drawing showing the channel system in blue lines, red dotted lines represent wrinkle ridges, the drainage basin is delimited in grey, and fan-shaped and deltaic deposits in orange. The total mapped length of the channel as shown here is ~325 km, and the flow direction is towards the east.

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by suja82 on March 31, 2016  •  Permalink
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Posted by suja82 on March 31, 2016

https://planetarygeomorphology.wordpress.com/2016/03/31/sedimentology-and-hydrology-of-an-amazonian-paleo-fluivo-lacustrine-systems-on-mars-moa-valles/

Experimental Delta Formation in Crater Lakes

Post by G. de Villiers, Faculty of Geoscience, Utrecht University.

Fan-shaped deposits have been identified on the surface of Mars (Image 1). These sediment bodies often occur within impact craters and, specifically in the cases of fan deltas, suggests that these craters were once lakes early in Martian history. Fan delta morphologies are indicative of upstream (e.g. flow discharge and sediment properties) and downstream (e.g. basin characteristics) parameters, from which the hydrological conditions at the time of formation can be inferred (e.g. Kleinhans et al. 2010).

IAGFigure1

Image 1: Examples of fan delta deposits on Mars, formed in enclosed impact crater or rift basins. A) Single-scarped, branched prograding delta (PSP_006954); B) Single-scarped, smooth prograding delta (I10805012); and C) Multiple-scarped, stepped retrograding delta (V17040003). White line is approximately 5 km.

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by Mary Bourke on August 1, 2014  •  Permalink
Posted in Experiment, Mars
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Posted by Mary Bourke on August 1, 2014

https://planetarygeomorphology.wordpress.com/2014/08/01/experimental-delta-formation-in-crater-lakes/

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