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 , Zimbelman, James R., Chair, Center for Earth and Planetary Studies, National Air and Space Museum, MRC 315, Box 37012, Washington, DC , Peterfreund, Alan R., Peterfreund Associates, 30 Boltwood Walk, Amherst, MA 01002; and Greeley, Ronald, Department of Geological Sciences, Arizona State University, Box , Tempe, AZ 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 Bedforms Steven H. Williams James R. Zimbelman Alan 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 M excerpt

?

Previous Work Large (“Granule-” / “Deflation-) Ripples: Kelso Dunes (California) Coachella Valley Rogers Dry 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) – Pumice66 wt %  = 1.8 – Obsidian11 wt %  = 2.1 Windward Slope (D = ~5 mm) – Pumice74 wt %  = 1.6 – Obsidian11 wt %  = 2.1 –More poorly sorted; skewed to fines Leeward Slope (D = ~5 mm) – Pumice26 wt %  = 1.6 – Obsidian37 wt %  = 2.2

Conclusions Some terrestrial large ripple bedforms are very long-lived Larger, but lighter, particles may be more mobile