Brief explanation:

Hornito (Spanish) = "Little oven".
Volcanic hornitos are small (usually a few meters high) rootless spatter cones that form on the surface of a (usually basaltic pahoehoe) lava flow. A hornito develops when lava is forced up through an opening in the cooled surface of a flow (a skylight) 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. (from USGS Photoglossary).