An example of a hornito on Hawaii that has built lava spatter deposits into a mound over its vent
Hornitos are formed in lava flows and are small openings that release small quantities of lava. Similar to spatter cones, Hornitos are rootless, meaning they don't sit on top of the main vent like spatter cones. Instead they are usually created by the slow upwelling of lava through the roof of a lava tube. High pressure causes lava to ooze and spatter out. The lava builds up on the surface and solidifies creating the initial structure. Hornitos can grow and exceed 10 meters in height.