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3 - A review of open-channel megaflood depositional landforms on Earth and 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 33-49
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Summary
Summary
Catastrophic out-bursts of water from lakes impounded by glacial ice or debris such as moraines have caused large freshwater floods on Earth in recent times at least back to the Quaternary. Resultant large-scale depositional sedimentary landforms are found along the courses of these floodwaters. On Mars, similar floods have resulted from catastrophic efflux of water from within the Martian crust. This latter conclusion is based on large-scale and mesoscale landforms that appear similar to those identified in flood tracts on Earth. Both on Earth and on Mars, these landforms include suites of giant bars – ‘streamlined forms’ – of varying morphology that occur primarily as longitudinal features within the floodways as well as in flooded areas that were sheltered from the main flow. Flow-transverse bedforms, notably giant fluvial dunes and antidunes also lie within the floodways. The flood hydraulics that created these forms may be deduced from their location and morphology. Some other fluvial landforms that have been associated with megafloods on Earth have yet to be identified on Mars.
Introduction
Exceptionally large freshwater floods on Earth are associated with the catastrophic draining of glacial lakes Missoula and Agassiz amongst others in North America (Teller, 2004). Other glacially related large floods occurred in the mountains of Eurasia, which have only recently received attention (Grosswald, 1999; Montgomery et al., 2004), and geomorphological evidence of other large floods may be discovered in formerly glaciated terrain on other continents.
6 - The morphology and sedimentology of landforms created by subglacial megafloods
- 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 78-103
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- Chapter
- Export citation
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Summary
Summary
Subglacial landforms across various scales preserve the history of movement, deposition and erosion by the last great ice sheets and their meltwater. The origin of many of these landforms is, however, contentious. In this chapter these forms are described both individually and as suites that make up entire landscapes. Their interpretations are discussed with reference to the megaflood hypothesis. A description is provided of individual forms via their size, shape, landform associations, sedimentology and the relationship between landform surfaces and internal sediments. The possible origins of each are then discussed. To simplify the chapter the landforms are categorised by their size (micro, meso, macro and mega), although, importantly, it should be noted that several landforms show similarities across scales. Also discussed is the relevant subglacial hydrology associated with the described forms, especially the volume and discharge rates of megaflood flows, and where water may have been stored prior to the megaflood events.
Introduction
As early as 1812, Sir James Hall interpreted the famous Castle Rock in Edinburgh, Scotland, a crag and tail, as a landform created by immense, turbulent floods. Likening the hill to features carved in snow by wind, he could only hypothesise that water was responsible; probably giant tidal waves, as, at that time, he knew of no other mechanism that could conceivably create such streamlining. It is now very clear that the streamlined forms first noted by Hall are part of a continuum containing landforms of many shapes and sizes.