High Valley basaltic andesite lava flow, Clear Lake Volcanic Field, California

This lava flow of basaltic andesite composition erupted in the High Valley area. The blocky appearance of this flow top is termed 'A'ā (pronounced "ah-ah"), which is a Hawaiian term for lava flows that have a rough rubbly surface composed of broken lava blocks called clinkers. USGS photo by Dawnika Blatter