From flow + top.
flowtop (plural flowtops)
- (geology) The solid crust on a moving lava flow.
- 2007 September 21, Jaeger et al., "Athabasca Valles, Mars: A Lava-Draped Channel System" in Science 317(5845), page 1710 [1]:
- they formed as gas vented from fixed sources at depth, ripping continuous openings through the moving flowtop.