Difference Between AA and Pahoehoe

AA vs Pahoehoe

Pahoehoe and AA might sound alien names to you but to those studying volcanoes and their lavas, these are names of two types of lava flows. Lava flow contains molten rocks and both Pahoehoe and AA are basaltic in nature. Both these names are Hawaiian in origin. The compositions of both Pahoehoe and AA are the same. There are many similarities between these lava flows though there are subtle differences mainly in their consistency and appearance that is going to be discussed in this article. 

What is AA Lava Flow?

This is a thick lava flow that is jagged in nature making it difficult for one to walk upon it even after it has cooled down. This lava has a very rough surface after cooling down. This roughness is a result of gas explosions that tear the external crust of the lava. If you look at it, you find rock fragments and blocks of rocks lying together but under this structure is the molten lava. You cannot hope to traverse AA lava type wearing rubber slippers as the clinker surface can cut through the rubber of the slippers. It is when lava flows at a rapid pace that AA lava is formed. Rapid flowing means lava loses heat quickly and its viscosity is pretty high.

What is Pahoehoe Lava Flow?

This type of lava flow has a ropy surface that is smooth. The surface texture of such a lava flow resembles that of a brownie pan. The smooth surface of the lava flow is indicative of the fact that the gases inside the lava have not been able to go out. Pahoehoe is more fluid than AA lava flow on this account. Under the ropy surface of this lava flow is hot and molten lava that keeps pushing forward creating a further ropy structure.

What is the difference between Pahoehoe and AA?

• Pahoehoe lava cools slowly while AA lava cools quickly.

• AA lava moves fast whereas Pahoehoe moves slowly.

• In the case of AA lava flow, gases have escaped from the upper surface creating clinkers and jagged outer structure.

• In the case of Pahoehoe lava flow, gases have not been able to escape the outer surface creating ropy and smooth surface.

• You can walk over cooled Pahoehoe lava flow wearing just rubber slippers while it is impossible to walk over AA lava flow without sturdy footwear.