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10 - Floods from fossae: a review of Amazonian-aged extensional–tectonic megaflood channels on Mars
- Edited by Devon M. Burr, University of Tennessee, Paul A. Carling, University of Southampton, Victor R. Baker, University of Arizona
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- Book:
- Megaflooding on Earth and Mars
- Published online:
- 04 May 2010
- Print publication:
- 24 September 2009, pp 194-208
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Summary
Summary
The four youngest megaflood channels on Mars – Mangala Valles, Marte Vallis, Grjotá Valles and Athabasca Valles – date to the Amazonian Period and originate at fissures. The channels show common in-channel morphological indications of flood activity (streamlined forms, longitudinal lineations, scour), as well as evidence for volcanic, tectonic, sedimentary and/or glacial/ground ice processes. The fissure sources and channel termini have varied expressions, suggesting various triggering mechanisms and fates for the floodwaters. Possible triggering mechanisms include magmatic processes (dyke intrusion), tectonic processes (extensional faulting) and a combination of both types of processes. Surface morphology suggests that each of these mechanisms may have operated at different times and locations. Upon reaching the surface, the water likely would have fountained at least a few tens of metres above the surface, producing some water and/or ice droplets at the fountain margins. The likely sources of the floodwater are subsurface aquifers of a few kilometres' thickness and a few tens of degrees Celsius in temperature.
Introduction
Megaflooding on Mars has varied in origin and amount throughout the history of the planet. During the Noachian Period, the most ancient period, flooding originated from crater basins (Irwin and Grant, this volume Chapter 11). During the Early Hesperian Epoch, megafloods originated at chaos terrain often set within Valles Marineris chasmata (Coleman and Baker, this volume Chapter 9). During the Amazonian Period, the most recent period, megaflooding originated from fossae produced by extensional tectonism.
16 - Dynamics of fluid flow in Martian outflow channels
- Edited by Devon M. Burr, University of Tennessee, Paul A. Carling, University of Southampton, Victor R. Baker, University of Arizona
-
- Book:
- Megaflooding on Earth and Mars
- Published online:
- 04 May 2010
- Print publication:
- 24 September 2009, pp 290-311
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- Chapter
- Export citation
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Summary
Summary
The conditions under which large volumes of water may have flowed at high speeds across the surface of Mars are considered. To assess the likely ranges of initial water temperature and release rate, the possible conditions in subsurface aquifers confined beneath the cryosphere are explored. Then the transfer of water to the surface in fractures induced by volcanic activity or tectonic events is modelled and the physical processes involved in its release into the Martian environment are discussed. The motion of the water across the surface is analysed with standard treatments for fluvial systems on Earth, modified for Mars by taking account of the differing environmental conditions and removing what may be considered to be the unsafe assumption that most channels involved bankfull flows. The most commonly discussed environmental difference is the smaller acceleration due to gravity on Mars. However, an important additional factor may have been the initially vigorous evaporation of water into the low-pressure Martian atmosphere. This process, together with the thermal losses incurred by assimilation of very cold rock and ice eroded from the cryosphere over which the water travels, causes minor changes in the depth and speed of a water flood but, eventually, produces major changes in the flood rheology as the total ice and sediment loads increase. The roles of these processes in determining the maximum distance to which the water may travel, and the relative importance of erosion and deposition in its bed, are discussed.