The two most prevalent types of lava worldwide, pahoehoe (pronounced pa-hoy-hoy) and aa (pronounced ah-ah), take their names from the native Hawaiian language.
The state of Hawaii is actually a chain of volcanic islands, where pahoehoe and aa are both found in abundance.
Pahoehoe has the shape of thick cords of rope or puffy billows. It can look something like black whipped cream. When highly fluid lava flows, the outer surface area congeals to form a thin, flexible exterior.
The lava inside continues to run, molding the outside layer into ropelike forms. These shapes remain when the entire mass solidifies.
Aa results from oozing semisolid lava. As aa flows, it carries rough, jagged shards of rock along its path. Aa hardens into sharp, splintery, knifelike edges.
You can walk comfortably on cold pahoehoe barefoot, but aa will slice the soles of your shoes.