variants
or a'a
geology
: basaltic lava having a rough, broken surface
This jumble of two-year-old black rock is of the type known as aa (pronounced ah-ah). This is the term borrowed from the Hawaiian language for lava that is broken, jagged and angular, in contrast to the smooth or rope-textured pahoehoe …—
Kendrick Frazier
Kendrick FrazierAa is formed from stiffer, more viscous lava with a thick brittle crust that becomes broken and heaped up as it is carried along by the molten lava beneath.—Science News
Science NewsThe same eruption of lava can switch from pahoehoe to a'a, depending on factors such as thickness and how fast it's cooling.—Gemma Tarlach
compare pahoehoe
Gemma Tarlach
ana
1
administrative assistant
2
Alcoholics Anonymous
3
antiaircraft
4
arachidonic acid
5
associate in arts
6
author's alterations
Cite this Entry
“Aa.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/aa. Accessed 31 Oct. 2025.
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