Which of the following is an extended definition of aa?
Hawaiian lava flows that solidify into sharp, jagged rock are called "aa." I always remember the name by imagining that trying to walk over these rough surfaces made ancient Hawaiians yell "ah! ah!" in pain.
An iron-rich lava forming irregular, broken rocks is called aa.
Aa lavas harden into jagged rocks, unlike pahoehoe lavas, which form smooth surfaces.
Aa is not an abbreviation; it is a noun that refers to a particular kind of igneous rock with a rough surface texture.