How fast does lava actually move?

I mean, they are standing there staring down a wall of moving molten mantle matter with presumably no place to escape other than over the cliff from whence Mark just rescued Abbey…

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Note the tree all aflame in the panel near Mark’s head… I’m sure that’s an interesting phenomenon watching the lava issue forth and items in its path reaching a level of spontaneous combustion… like a tree that had, only seconds before that, been alive and vital and full of life force… Mark and Abbey better take a cue from that before they both spontaneously combust…