Over Two Decades at Mono Domes:Slow Changes to Potential Analogs to Martian

Aeolian Bedforms

Williams, Steven H., Chair, Education Division, National Air and Space Museum, MRC 305, P.O. Box 37012, Washington, DC 20013-7012, williamss@nasm.si.edu; Zimbelman, James R., Chair, Center for Earth and Planetary Studies, National Air and Space Museum, MRC 315, Box 37012, Washington, DC 20013-7012, jrz@nasm.si.edu; Peterfreund, Alan R., Peterfreund Associates, 30 Boltwood Walk, Amherst, MA 01002; and Greeley, Ronald, Department of Geological Sciences, Arizona State University, Box 871404, Tempe, AZ 85287-1404

NOTE: View this presentation in “Notes Page” mode to see commentary. This is not a transcript of the talk as delivered at GSA 2003 in Seattle, but the Notes comments convey the content and flavor of the remarks as delivered at GSA!

Over Two Decades at Mono Domes:

Slow Changes in Potential Analogs to Martian Aeolian

BedformsSteven H. Williams

James R. ZimbelmanAlan R. Peterfreund

Ronald Greeley

Large “Ripples”

Large Ripples on Mars

• Hinted At in Viking Images

• Common and Widespread

• Overlain by Dunes and Debris

• Some Atop Dunes

Dunes Override Ripples

Floor of Crater Kaiser

Ripples Override Dunes

M2000635 excerpt

?

Previous Work

Large (“Granule-” / “Deflation-) Ripples:

• Kelso Dunes (California)• Coachella Valley• Rogers Dry Lake @ Edwards AFB• Great Sand Dunes National Monument• Coyote Playa

All involve granules or coarser materials

Problem!

• Terrestrial Granule Ripples are fragile– Prone to removal– Prone to burial by mobile sand

• BUT: On Mars, at least some large ripples appear to be older and more durable than their terrestrial counterparts

So – do we have the “best” analogs?

Mars “Ripples” Are Old (?)

• Note debris apron overlies ripples• Implies ripples long-lived• Implies they are more durable than typical terrestrial granule ripple

Not All Large Ripples Involve Granules!

• What if particles involved are distinguished by density, not by size?

• Candidate examples: Pumice

• Low density allows larger particles to move and create bedforms

• Field Example: Mono Domes, California

Large ripples in pumice/obsidian

South Mono Dome, California

Minimal changes over ~22+ years

June, 2003

May, 1981

June, 2003

Bedform Comparison

May, 1981

June, 2003

May, 1981

Bedform Comparison

Ripple Crest Alteration

Raked

Stomped

Typical Bedform Profile

Sedimentary Characteristics• Bedform Crests (D = 1.2 cm)

– Pumice 66 wt % = 1.8– Obsidian 11 wt % = 2.1

• Windward Slope (D = ~5 mm)

– Pumice 74 wt % = 1.6– Obsidian 11 wt % = 2.1– More poorly sorted; skewed to fines

• Leeward Slope (D = ~5 mm)

– Pumice 26 wt % = 1.6– Obsidian 37 wt % = 2.2

Conclusions

• Some terrestrial large ripple bedforms are very long-lived

• Larger, but lighter, particles may be more mobile