| − | '''Aa''' (pronounced "ah-ah" - a [[Hawaii]]an term), is [[lava]] that has a rough, jagged, spiny, and generally clinkery surface. In thick aa flows, the rubbly surface of loose clinkers and blocks hides a massive, relatively dense interior. <ref>[http://vulcan.wr.usgs.gov/Glossary/volcano_terminology.html Glossary of Volcano and Related Terminology (Tilling, Heliker, and Wright, 1987)]</ref>
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