GEO 330 Lecture Notes - Lecture 29: Dark Slope Streak, Volumetric Heat Capacity, Dune
14 May 2018
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Wind streaks are elongated albedo markings downstream of topographic obstacles (usually
craters)
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Wind tails are accumulations of debris downwind of rocks observed by landers on the surface
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Bright depositional streaks
1.
Dark erosional streaks
2.
Dark depositional streaks
3.
Frost streaks
4.
Four types of wind streaks recognized:
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Form downwind of craters and other positive relief features, mostly at low southern
latitudes and in the northern plains
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Bright depositional streaks are most common
•
Directions correlate well with wind directions predicted by GCMs
○
Probably form mostly by deposition of dust during the final stages of dust storms
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Bright depositional wind streaks in Tharsis and Elysium show seasonal changes
•
Reasons(s)?
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Some bright depositional streaks noticeably affect the thermal inertia of the surface. Others do
not
•
Form in late southern summer and fall and are destroyed during the following dust storm
season
○
Probably form due to turbulence that occurs downstream of obstacles, which removes dust
○
Dark erosional streaks form downwind of obstacles
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Dark depositional streaks form downwind of sedimentary deposits, usually sand dunes within
craters
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Thermal inertia indicates they are composed of sand-sized particles
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Observed lengthening indicates saltation of sand grains
•
Frost streaks are accumulations of CO2frost downwind of obstacles
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Wind may or may not be directly involved in their formation
○
Dark streaks also occur on dust-covered slopes, perhaps due to “dust avalanches”
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Dark slope streaks occur in low thermal inertia terrain
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These streaks appear to be forming today, and they fade over time
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Most likely due to slope failure and exposure of underlying dark material
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Wind Streaks and Tails
Term used for both free-standing accumulations and features on other eolian landforms
such as dunes
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Ripple refers to accumulations of wind-blown debris that have wavelengths that are a few cm to m
across
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Megaripples refer to linear, parallel ridges of material that have wavelengths between a few m to
25m
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Dunes generally refer to features greater than 25m across
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Size is used as definition, but formation mechanisms not necessarily the same for each of the
three features
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Ripples form by movement of saltating sand particles
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Wind-facing slopes are eroded by the saltating particles and lee slopes are protected from wind
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Ripple moves downwind with a wavelength controlled by the saltation path length
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Sharp (1963) suggested that ripple height controls wavelength
•
Ripples form mostly on dune surfaces where sand source is well sorted
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Megaripples generally form when there is a bimodal size distribution of particles
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Dunes, Ripples, and Drifts
Wind and Sedimentary Processes
Wednesday, May 9, 2018
5:54 PM
GEO 330 Page 1
Document Summary
Wind streaks are elongated albedo markings downstream of topographic obstacles (usually craters) Wind tails are accumulations of debris downwind of rocks observed by landers on the surface. Form downwind of craters and other positive relief features, mostly at low southern latitudes and in the northern plains. Bright depositional wind streaks in tharsis and elysium show seasonal changes. Directions correlate well with wind directions predicted by gcms. Probably form mostly by deposition of dust during the final stages of dust storms. Some bright depositional streaks noticeably affect the thermal inertia of the surface. Form in late southern summer and fall and are destroyed during the following dust storm season. Probably form due to turbulence that occurs downstream of obstacles, which removes dust. Dark depositional streaks form downwind of sedimentary deposits, usually sand dunes within craters. Thermal inertia indicates they are composed of sand-sized particles. Frost streaks are accumulations of co2 frost downwind of obstacles.
