Mars and clathrate flows
http://themis.la.asu.edu/mars-bin/mars_cgi_map.pl?CENT_LAT=-9.831532648&CENT_LON=120.10478&RESCALE=64&TNAIL_LINK=20020520a
In this picture pit tubes can be seen, both in series to the southeast of the crater, as well as one particular pit tube crossing the crater itself!
Note that where the pit tubes on the north and south rims collapsed, their edges are quite distinct: they have not been buried by lava flows.
Now note the flows at the bases of these two collapses: they are smooth, and not the jumble that would have come down from a rock (solid lava) collapse. Further, since the edges of the pit tube collapses themselves are not buried by lava flows, the flows can not be lava flows.
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