Could be more adapted to the text.

"Cracking" or "fine cracking".

"Craquelure" implies a finer crack than the French "fissure"="crack/fissure", and also tends to imply a network of intersecting cracks (cracks due to ground movement and settlement might be preferentially oriented, but shrinkage cracks would be in all directions). In other contexts one might talk of "hairline cracks", but they are probably considerably lava in larger flows.

I'd avoid "fissure", if only because my Penguin Dict of Geology says that "a lava flow may arise from a central-type vent or a fissure", so a fissure is (supposedly and initially) considerably larger than the cracking that subseuqntly occurs in the flow itself.

craquelure de dessèchement - suncrack, shrinkage crack [Dict. of Earth Science, Michel & Fairbridge, Masson] (though I can't help wondering if this applies more to the mudcracks you see in drought areas).