riparian rap

Martian water in Carbondale, Illinois.

McEwen et al.’s Science paper on Martian water yesterday is exciting stuff!

Especially for us, because our models can simulate fluvial geomorphology on Mars.  The plastic media we use is particularly good at forming sapping channels, which are groundwater-driven gullies.  Here you see Earthling Callan Bentley observing a few in our lab.  In this photo we’ve just lowered the standpipe (base level), and initiated several sapping channels.

For us the sapping channels are sometimes an unwanted feature.  They form because the coarser mixes we use allow free subsurface flow, which emerges with enough volume to erode the particles and form channels.

Just like on Mars, probably.  This stunning image of the Nanedi Valles (click to enlarge, via) shows tributaries to the main meandering thread that are probably sapping channels — these appear at the center and lower right.

Ryan Anderson’s “The Martian Chronicles” blog gives a nice overview of these features in his roundup of talks from a 2008 AGU meeting.

Today’s Times article has more links.

And I have to give props to the late great Marie Morisawa, who taught me “sapping channels, unlike gullies formed by overland flow, have round heads.”

UPDATE:  JPL press release with links to images and analysis.

Top photo via NY Times, credit to NASA/JPL-Caltech/Univ. of Arizona