Rounded tephra balls between 2 mm and 64 mm in diameter are
called accretionary lapilli if they consist of tiny ash particles. Volcanic
ash sometimes forms such balls in an eruption column or cloud, owing
to moisture or electrostatic forces. Lapilli (singular: lapillus) means
"little stones" in Italian.
|These accretionary lapilli on the surface of the
Ka`u Desert south of Kilauea caldera. The lapilli formed during explosive
eruptions of Kilauea in 1790. Credit: U.S. Geological Survey
|Layer of tephra consisting of accretionary lapilli
surrounded by wind-deposited ash in the Ka`u Desert, Kilauea Volcano.
This layer is one of several found at this location, about 10 km from
Kilauea's summit caldera. Credit: U.S. Geological Survey
AND PLANETARY SCIENCE
Source: U.S. Geological