The Dictionary, Pg 1: AA

The "Dictionary" of course is The Official Scrabble Dictionary, 4th edition.

Glowing `a`a flow front advancing over pahoehoe on the coastal plain of Kilauea Volcano, Hawai`i.

AA - A rough cindery lava

From the US Geological Survey:

A`a (pronounced "ah-ah") is a Hawaiian term for lava flows that have a rough rubbly surface composed of broken lava blocks called clinkers. The incredibly spiny surface of a solidified `a`a flow makes walking very difficult and slow. The clinkery surface actually covers a massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an `a`a flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an `a`a flow.

CLINKERS is in The Dictionary. "to form residue while burning." So is PAHOEHOE (which is in the description of the photo on the copyright free USGC site and used above).

"sooth solidified lava."

So is LAVA of course: "molten rock that issues from a volcano."

and

PAHOEHOE - smooth, ropy, hummocky lava

LAVALIKE: "resembling lava"