aa

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1. dung nham aa

   A form of lava flow associated with Hawaiian-type volcanoes, consisting of basaltic rock, usually dark-colored with a jagged and loose, clinkery surface. Compare pahoehoe.

   uncountable

   We...saw ‘pahoihoi’ or solid lava forming, and also ‘aa’ or clinkers.

   Cooling and solidification frequently takes a different course [...] in lava flows, producing the clinker-like ‘aa’ lava.

   Both pahoehoe and aa lava flows are common on the upper slopes of Mauna Loa with a preponderance of aa flows found at the lower elevations.