VHP Photo Glossary: Lava balls
Accretionary lava balls
Accretionary lava balls are roughly spherical masses that form on the surface of an `a`a flow. They range in size from a few centimeters to several meters in diameter. Lava balls grow when a small fragment of solidified lava rolls along the surface of an active flow and lava sticks or accretes to its surface. The growth of a lava ball is similar to the way a giant snowball grows when soft, sticky snow adheres to its surface as it rolls downslope.
Glowing accretionary lava balls, pictured, (bottom, 0.75 m in diameter) in front of moving `a`a flows. Both flows were erupted from Pu`u `O`o vent on the east rift of Kilauea Volcano, Hawai`i.