Pillow lavas are volumetrically the most abundant type because they are erupted at ocean ridges and because they make up the submarine portion of seamounts and large intraplate volcanoes, like the Hawaii-Emperor seamount chain. Pahoehoe is the second most abundant type of lava flow. Eruptions under water or ice make pillow lava. Pillow lavas have elongate, interconnected flow lobes that are elliptical or circular in cross-section.
Pahoehoe lava is characterized by a smooth, billowy, or ropy surface.
Pahoehoe flows tend to be relatively thin, from a few inches to a few feet thick. In map-view the flows tend to be narrow and elongate. Aa is characterized by a rough, jagged, spinose, and generally clinkery surface. Aa lava flows tend to be relatively thick compared to pahoehoe flows. Pictures in Hawaiian Tour Guide illustrate many of the points noted above.