Distal-type 'a'a flows. In A, which shows the top half of a ~6 m-thick flow margin during the 1984 Mauna Loa eruption, the incandescent lava could not be perceived to flow and the main activity consisted of little particles of incandescent sand-sized particles sliding down the flow edge. Occasionally a large dense block would also tumble down off the top of the flow. Additionally, we could not penetrate the incandescent lava with a stick. In B, a pre-contact Kilauea flow, note the blockiness of the top layer and the massive, non-vesicular quality of the interior. Hammer (arrow) for scale.

VolcanoWorld