GEO 330 Lecture Notes - Lecture 28: Aeolian Processes, Dust Devil, Wind Speed
14 May 2018
School
Department
Course
Professor
Dust devils
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Sand grain saltation
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Global dust storms
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Action of wind on the Martian surface has been observed
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Sand ripples and dunes are found all over Mars and are clear evidence for wind activity
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Major volcanic constructs not significantly modified by wind
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Poorly coherent, layered sedimentary rocks can be significantly eroded
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Wind
Most rock debris easily moved by wind is quartz sand derived by the mechanical breakdown of
granitic rocks
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Sand spends relatively short time on surface participating in eolian processes before being
transported to oceans
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Once in ocean, sand is buried, lithified, and incorporated into sedimentary rock record
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Tectonic forces may move sandstones back to the surface where sand can again be acted upon by
wind
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Inventory of materials can be easily moved by wind and recycled on geologic time scales
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Cycling of Fragmental Debris -- Earth
Quartz-rich granitic rocks are a very minor component of surface
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Burial of debris in oceans has been very limited if it has occurred at all (at least since the end of
the Noachian)
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Recycling of marine rocks by tectonics has not occurred
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Fragmental material produced at the surface generally remains available for a long time to be
moved by wind and participate in eolian processes
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Much loose debris at the surface may be ancient, when volcanic, impact, and erosional processes
occurred at a much higher rate
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Post-Noachian deposition of loose debris to the surface has probably been minor (except locally
near impact craters)
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Cycling of Fragmental Debris -- Mars
Earth -- fragmental material is rapidly removed from the surface and incorporated into the rock
record
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Mars -- fragmental material remains at the surface for billions of years to participate in eolian
processes
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Thick sedimentary deposits have formed on Mars (such as the Medusa Fossae Formation and
Meridiani Planum) but they remain at the surface, where they can be eroded by wind
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Cycling of Fragmental Debris -- Summary
Suspension in atmosphere
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Saltation (bouncing of particles across the surface)
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Creep (slow movement of particles across the surface as they are impinged upon by other
particles)
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Transportation of material by wind:
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Movement of particles > 1mm is mostly by creep
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Particles 100-1000µm in size move mostly by saltation
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Particles < 100 µm in size move mostly in suspension
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Factors such as surface roughness, wind speed and (on Earth) vegetation can affect exact numbers
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Cycling of Fragmental Debris -- Entrainment of Particles by Wind
Wind and Sedimentary Processes
Wednesday, May 9, 2018
5:54 PM
GEO 330 Page 1
Document Summary
Action of wind on the martian surface has been observed. Sand ripples and dunes are found all over mars and are clear evidence for wind activity. Major volcanic constructs not significantly modified by wind. Poorly coherent, layered sedimentary rocks can be significantly eroded. Most rock debris easily moved by wind is quartz sand derived by the mechanical breakdown of granitic rocks. Sand spends relatively short time on surface participating in eolian processes before being transported to oceans. Once in ocean, sand is buried, lithified, and incorporated into sedimentary rock record. Tectonic forces may move sandstones back to the surface where sand can again be acted upon by wind. Inventory of materials can be easily moved by wind and recycled on geologic time scales. Quartz-rich granitic rocks are a very minor component of surface. Burial of debris in oceans has been very limited if it has occurred at all (at least since the end of the noachian)
