Global Volcanism Program | Image GVP-03500
Two types of lava flows, pahoehoe (left) and `a`a (right), are different textural forms of otherwise identical lava. The different textures relate to different flow dynamics and both can form in the same lava flow. Because of differential weathering rates, the overlying pahoehoe flows look younger than the associated aa flows, and the two flows are easily mistaken for flows of greatly differing age.
Photo by Lee Siebert, 1987 (Smithsonian Institution).