OVER TWO DECADES AT MONO DOMES: SLOW CHANGES TO POTENTIAL ANALOGS TO MARTIAN AEOLIAN BEDFORMS

Aeolian bedforms with wavelengths intermediate between those of ripples and dunes are more common on Mars than was realized prior to the analysis of Mars Global Surveyor data. Such bedforms are rare on Earth, and, in all cases, involve sedimentary materials of mixed size. The best Viking images hinted at their presence, and fostered research into possible terrestrial analogs. One of the first field analog sites to be considered lies atop the Mono Domes eruptive complex near Mammoth Mountain, California, where large fragments of pumice and smaller fragments of obsidian are sculpted into large ripple-like bedforms. Detailed grain size analysis from different locations on the bedforms was part of the initial study, as was marking bedforms with rebar in order to assess bedform migration over time, and placement of abrasion targets. The site was revisited in June, 2003, more than 22 years after the initial observations. Unfortunately, South Dome has been a popular OHV recreation site, despite closure by the BLM to all motorized traffic, and all of the abrasion targets and almost all of the rebar were damaged and/or removed. However, photographic documentation demonstrates than none of the larger bedform elements has moved significantly since they were first observed. Footprints and tire tracks were “repaired” naturally, and some changes were noted in the smallest of aeolian features, but the bedforms themselves are unchanged. Ripple crests were flattened in two test plot locations in 1981. In one, the fragments comprising the crest were removed by gentle raking; in the other, the fragments were pressed into the subsurface by treading on them heavily. Neither bedform crest has been restored since the plots were established. The apparent longevity of the Mono Domes bedforms is consistent with that of their potential martian analogs, which appear to be older and more durable than would be expected of aeolian bedforms developed in unconsolidated sediments.