Lava blades are projections from the wall that tend to be parallel and regularly spaced. They grade from thin to thick, as shown in the two photos. The edges may be smooth or stringy and associated with strands of Pele's hair. They often occur near constrictions (as in the bottom photo) and the edges of lava falls: places where the velocity of the flowing lava may have been increased (by wind in the first case and gradient in the second) 
The thicker blades in the lower photo may have begun as thin blades that were then coated by upwelling lava, like sharktooth stalactites and splash stalactites.
Blades are relatively uncommon outside of Hawaiian lava tubes, but a more common, and possibly related formation is the "castellations, " commonly seen on the edges of levees. Long shelves of small lava blades occur in some caves in New Mexico's El Malpais. 

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Created: August 4, 2000
Author: Dave Bunnell