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.

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.

Variant of acetic acidInitialism of acetic acid.

Variant of acting ageInitialism of acting age.

Variant of alveolar-arterialInitialism of alveolar-arterial.

Variant of aminoacetoneInitialism of aminoacetone.

Variant of amino acidInitialism of amino acid.

Variant of approximate absoluteInitialism of approximate absolute.

Variant of arachidonic acidInitialism of arachidonic acid.

Variant of armature acceleratorInitialism of armature accelerator.

Variant of ascending aortaInitialism of ascending aorta.

Variant of atomic absorptionInitialism of atomic absorption.

Variant of author's alterationInitialism of author's alteration.

Variant of average audienceInitialism of average audience.

Variant of arctic-alpineInitialism of arctic-alpine.

Variant of always afloatInitialism of always afloat.

Variant of adjectivesAbbreviation of adjectives.

Variant of arteriesAbbreviation of arteries.

Variant of anaAbbreviation of ana (“of each, equal parts”).

I.