When bodies of partially hardened lava are pulled apart, by gravity or by flowing lava, stretch marks may result as shown in the first photo. Here, the stretched lava is on a portion of wall that has been pulled downflow by the lava stream. Stretched lava may also occur when a crusted floor slumps down on top of a contracting lava lake. Sometimes strands of lava, like stretched taffy, adhere to the two surfaces pulled apart, as shown in the lower photo.
AUTHOR: Dave Bunnell