Chemically similar basaltic lavas may exhibit grossly different surface characteristics under different physical conditions, notably rate of flow. Pahoehoe flows (left) have grey glassy, shiny surfaces which are generally smooth when fresh, and form curious plastic patterns of ropes and whorls with dimensions of a few centimeters to a few meters. Individual flow lobes are rarely more than a meter thick, and are typically 10-20 cm. They form at low rates of flow. At higher rates of flow, internal shearing shreds the lava, and highly irregular, angular scoriaceous fragments result forming a'a flows (reddish colored, right side). Individual fragments may range up to a meter or more in size, though those seen here are 10-20 cm in diameter. Both lavas seen here were erupted within a short time of each other during the 1969-74 eruption of Mauna Ulu, Hawaii. (Fig. 7.9).

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