Pahoehoe flow from January 1947 A'a lava is a sharp, jagged, and rocky lava. It is very viscous, and therefore moves slowly. As it does move, it begins to cool. The crust that it forms continues to brake up causing that cracked, broken appearance. Pahoehoe is the more common lava type.
Pahoehoe is a smooth, ropey lava that forms as a result of gassy eruptions.
As it flows, it forms a crust that insulates the lava inside. Therefore creating lava tubes.