Photograph by D.A. Swanson on 21 May 1970
Hornito
A small rootless spatter cone that forms on the surface of
a basaltic lava flow (usually pahoehoe) is called a hornito.
A hornito develops when lava is forced up through an opening
in the cooled surface of a flow and then accumulates around
the opening. Typically, hornitos are steep sided and form conspicuous
pinnacles or stacks. They are "rootless" because they are
fed by lava from the underlying flow instead of from a deeper magma
conduit.
This hornito formed on the surface of a pahoehoe flow during the
Mauna Ulu eruption on the east rift zone of Kilauea Volcano, Hawai`i.
More about hornitos