Tsunamis on Mars: Earth analogues of projected Martian sediment (original) (raw)
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Martian gullies and their Earth analogues: introduction
Geological Society, London, Special Publications
Martian gullies are widespread landforms in the mid-latitudes of Mars. When the first reports of these kilometre-scale features were published in 2000, they were controversially hailed as a sign of recent flows of liquid water on the surface of Mars. This supposition was contrary to our understanding of recent environmental conditions on Mars, under which water should not exist in its liquid form. In response to their discovery, researchers proposed a wide range of scenarios to explain this apparent paradox, including scenarios driven by CO2, climate change or the presence of a liquid water aquifer. This Special Publication is a collection of papers arising from the topics discussed at the Second International Workshop on Martian Gullies held at the Geological Society, London. A review paper opens the Special Publication and thereafter the papers are presented under three themes: Martian remote sensing, Earth analogues and laboratory simulations. This Special Publication establishes...
A new dry hypothesis for the formation of martian linear gullies
Icarus, 2013
Long, narrow grooves found on the slopes of martian sand dunes have been cited as evidence of liquid water via the hypothesis that melt-water initiated debris flows eroded channels and deposited lateral levées. However, this theory has several shortcomings for explaining the observed morphology and activity of these linear gullies. We present an alternative hypothesis that is consistent with the observed morphology, location, and current activity: that blocks of CO 2 ice break from over-steepened cornices as sublimation processes destabilize the surface in the spring, and these blocks move downslope, carving out levéed grooves of relatively uniform width and forming terminal pits. To test this hypothesis, we describe experiments involving water and CO 2 blocks on terrestrial dunes and then compare results with the martian features. Furthermore, we present a theoretical model of the initiation of block motion due to sublimation and use this to quantitatively compare the expected behavior of blocks on the Earth and Mars. The model demonstrates that CO 2 blocks can be expected to move via our proposed mechanism on the Earth and Mars, and the experiments show that the motion of these blocks will naturally create the main morphological features of linear gullies seen on Mars.
Icarus, 2007
A new survey of Mars Orbiter Camera (MOC) narrow-angle images of gullies in the 30 • -45 • S latitude band includes their distribution, morphology, local topographic setting, orientation, elevation, and slopes. These new data show that gully formation is favored over a specific range of conditions: elevation (−5000 to +3000 m), slope (>10 • ), and orientation (83.8% on pole-facing slopes). These data, and the frequent occurrence of gullies on isolated topographic highs, lead us to support the conclusion that climatic-related processes of volatile accumulation and melting driven by orbital variations are the most likely candidate for processes responsible for the geologically recent formation of martian gullies.
A Closer Look at Water-Related Geologic Activity on Mars
Science, 2007
Water has supposedly marked the surface of Mars and produced characteristic landforms. To understand the history of water on Mars, we take a close look at key locations with the High-Resolution Imaging Science Experiment on board the Mars Reconnaissance Orbiter, reaching fine spatial scales of 25 to 32 centimeters per pixel. Boulders ranging up to ∼2 meters in diameter are ubiquitous in the middle to high latitudes, which include deposits previously interpreted as finegrained ocean sediments or dusty snow. Bright gully deposits identify six locations with very recent activity, but these lie on steep (20° to 35°) slopes where dry mass wasting could occur. Thus, we cannot confirm the reality of ancient oceans or water in active gullies but do see evidence of fluvial modification of geologically recent mid-latitude gullies and equatorial impact craters.
Sinuous gullies on Mars: Frequency, distribution, and implications for flow properties
Journal of Geophysical Research, 2010
1] Recent gullies on Mars are suspected to be the result of liquid-water-bearing flows. A formation from wet flows has been challenged by studies invoking granular (dry) flows. Our study focuses on the sinuous shapes observed for some of the recent Martian gullies. Sinuous gullies are found in locations and slopes (of 10°-15°) similar to straight gullies, and they are therefore related to the same formation processes. Numerical simulations of granular flows are performed here by introducing topographic variations such as obstacles, roughness, or slope changes that could possibly generate flow sinuosity. None of these simulations was able to reproduce sinuous shapes on a slope lower than 18°with friction angles typical of dry granular material. The only way to simulate sinuous shapes is to create small-amplitude periodic variations of the topography of the deposit, an origin not supported by current Martian imagery. Given the presence of sinuosity in natural terrestrial debris flows, we have concluded that sinuous Martian gullies are better reproduced by liquid-water-bearing debris flows. Sinuous shapes in leveed flows are used to derive mechanical parameters from several Martian gullies using photoclinometry. Values in yield strength of 100-2200 Pa, velocities of 1.1-3.3 m s −1 , and viscosities from 40 to 1040 Pa s are found, which are all within the range of values for terrestrial debris flows with various proportions of liquid water (20%-40%).
Initiation and flow conditions of contemporary flows in Martian gullies
Journal of Geophysical Research: Planets
Understanding the initial and flow conditions of contemporary flows in Martian gullies, generally believed to be triggered and fluidized by CO 2 sublimation, is crucial for deciphering climate conditions needed to trigger and sustain them. We employ the RAMMS (RApid Mass Movement Simulation) debris flow and avalanche model to back calculate initial and flow conditions of recent flows in three gullies in Hale crater. We infer minimum release depths of 1.0-1.5 m and initial release volumes of 100-200 m 3. Entrainment leads to final flow volumes that are ∼2.5-5.5 times larger than initially released, and entrainment is found necessary to match the observed flow deposits. Simulated mean cross-channel flow velocities decrease from 3-4 m/s to ∼1 m/s from release area to flow terminus, while flow depths generally decrease from 0.5-1 to 0.1-0.2 m. The mean cross-channel erosion depth and deposition thicknesses are ∼0.1-0.3 m. Back-calculated dry-Coulomb friction ranges from 0.1 to 0.25 and viscous-turbulent friction between 100 and 200 m/s 2 , which are values similar to those of granular debris flows on Earth. These results suggest that recent flows in gullies are fluidized to a similar degree as are granular debris flows on Earth. Using a novel model for mass flow fluidization by CO 2 sublimation we are able to show that under Martian atmospheric conditions very small volumetric fractions of CO 2 of ≪1% within mass flows may indeed yield sufficiently large gas fluxes to cause fluidization and enhance flow mobility.
Small-scale morphologic properties of martian gullies: insights from analysis of HiRISE images
2008
The discovery of abundant, geologically recent gullies on Mars in Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images [1] has led to numerous studies examining potential mechanisms for recent fluid or fluid-rich surface processes [e.g., 1-2]. The process or processes involved in Martian gully formation provide important insights into Martian geologic and volatile history. New gully deposits have been found in comparison of MOC images acquired over the extent of the MGS mission [3], leading to consideration of contemporary fluid activity. Gullies appear to be the youngest features in most locations [4], serving as evidence of geologically recent surface flow and erosive processes [5].
Journal of Geography (Chigaku Zasshi)
Gullies were not only investigated for scientific endeavor, but also were prime targets for the search for presence of water and life on Mars, as habitats might have or are existing. Gullies on Mars were first identified in the milestone paper by Malin and Edgett in 2000. Since then more than 174 papers were published on Martian gullies. A typical gully consists of an upper theatre-shaped alcove that tapers downslope to converge on a channel that extends further downslope to terminate in a triangular apron of deposited material. A number of processes were proposed for gully formation. These include liquid-induced processes, such as overland flow, headward sapping, debris flow, and other wet mass movements. The formation of liquid is attributed to groundwater sapping, to supply from deep subsurface aquifers by cryovolcanic processes, to melting of snow or melting of ground ice from surficial to shallow depths. Liquid-free mass movements, such as dry granular flows and dry ice outbreak, are also invoked as formation processes. Supporting and opposing morphologic evidence is shortly discussed. Tens of thousands of individual gullies were identified on Mars, which are concentrated on mid-to high-latitudes in both hemispheres. Gullies might have been active from 3 Ma ago to present. Future research may learn lessons from terrestrial gully research. On Earth, linear gullies may gradually develop oversteepened sidewalls, which in turn initiate deep-seated mass movements. Such systems are named gully complexes. Gullying can also be induced by sliding. Such landforms were termed slide complexes. These process sequences may occur also on Mars. In future investigations, identification of such complexes on Mars requires a focus on phases of incision and infilling to elucidate gully evolution.
Evidence of gully formation by regional groundwater flow in the Gorgonum–Newton region (Mars)
Icarus, 2005
The discovery of gullies on Mars suggests liquid water activity near the surface of the planet in recent times, Since liquid water is unstable under the present-day P-T martian conditions, the formation mechanisms of the gullies, and the source of the putative water, have been a matter of debate for the last years. To provide new insights into these matters, we have approached the problem studying the gullies in relation to their regional setting. A major point in our study relates to the geographic orientation of gullies, an aspect that has been previously regarded as a crucial matter in different models, and has profound implications regarding their origin. We present a comprehensive and detailed survey of the Gorgonum-Newton region, and a study of the Dao and Nirgal Yallis regions. The survey was carried out with the aid of965 high-resolution MOC images (752 for Gorgonum-Newton, 102 for Nirgal Yallis and III for Dao Yallis regions), and MOLA-derived DEMs. We found that gullies display a clear regional pattern, geographically and topographically consistent with a decreasing regional slope.