Southward from San Antonio to the Next Waypoint |
Southward from San Antonio to the Next Waypoint |
Apr 2 2010, 03:38 AM
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#1
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Member Group: Members Posts: 139 Joined: 14-October 05 From: Toronto, Canada Member No.: 529 |
It seems about the right time to start a new thread as we have now turned East to Endeavour.
Hope no one minds... -------------------- -- Robin
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Apr 4 2010, 03:05 PM
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#2
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Senior Member Group: Members Posts: 3008 Joined: 30-October 04 Member No.: 105 |
The ripples are changing because of an increase in wind velocity.
When we reached Concepcion we noticed the presence of transverse dunes (ripples), which suggested either an increase in sand availability or an increse in wind velocity. I initially thought of an increase in sand supply since there is a great deal of weathering of the fragmented rock around the fresh crater, but as we traveled southward ("upwind") of the crater, the transverse dunes were still present and by the time we got to the older, weathered San Antonio craters, we also started seeing scalloping of sand on the ripple crests (erosion). Concepcion was on the crest of a slight topographic high and the surface to San Antionio is essential flat or with a slight southward dip, and from the Tim Parker topo map, we see that the elevations decrease sharply to the south and southeast. Air moving in a laminar flow at altitude encounters the hillside and since the cross-sectional flow area is decreased, the velocity will increase due to a venturi effect. You can also see an increase in bare bedrock areas between here and "mini-Endurance", which I had hoped would be an indication of a change in lithology due to a drop in elevation, but, alas, appears to be less sand because of more wind... Attached is a drawing illustrating the orographic effect, adapted from an earlier topo x-section by fredk. --Bill -------------------- |
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