Here's why:
* Aa (pronounced "ah-ah") is a Hawaiian term for this type of lava flow.
* It's characterized by its rough, blocky, and fragmented surface, which forms as the lava cools and solidifies.
* The sharp, angular projections are a result of the lava's viscosity and the way it breaks apart as it cools.
In contrast:
* Pahoehoe lava flows are smoother and more ropey in appearance.
* Pillow lavas form underwater and have a rounded, pillow-like shape.
