A'a is characterized by:
* Rough, jagged surface: It's a very blocky, sharp and uneven flow.
* Slow-moving: It moves much slower than other lava types, like Pahoehoe.
* Thick and viscous: It's thicker and more viscous than Pahoehoe, making it difficult to flow easily.
How A'a forms:
* When lava cools and solidifies, it forms a crust on the surface.
* As the lava continues to flow beneath the crust, the crust breaks up into sharp, angular fragments called clinkers.
* These clinkers are then carried along with the lava, creating the rough, jagged surface of an A'a flow.
Other possible meanings:
While A'a is the most common meaning of "AA" in Earth Science, there might be other, less common uses. For example:
* AA could potentially be used as an abbreviation for "Angular unconformity", which refers to a geological feature where older rock layers are tilted or folded and then eroded before newer rocks are deposited on top.
* AA could also be used as a shorthand for "absolute age", which refers to the actual age of a rock or fossil, determined by radioactive dating methods.
However, these are less common uses compared to A'a lava flows. If you encounter "AA" in an Earth Science context, the most likely meaning is A'a lava.
