Cinder cones are large mounds that develop around volcanic vents, made up of tiny pieces of falling lava that get distributed during an eruption. In an eruption, hot, pressurized lava may be spewed skyward. Upon contact with cool air, the airborne lava at least partially solidifies, preserving tiny bubbles created by escaping gases. The light, hole-filled rocks, called cinders, accumulate around the vent and form a cone-shaped hill. Once settled, fragments may melt or weld together.
Cinder cones can range in size from tens to hundreds of meters in height. Within Hawai'i Volcanoes National Park, one of the most visible examples is Pu'u Pua'i (meaning "gushing hill" in Hawaiian), which formed due to the 1,900 foot lava fountains that occured during the eruption of Kīlauea Iki in 1959. Over the course of the thirty-six day eruption, cooling cinders continued to accumulate in a mound, eventually reaching a height of over 400 feet.
Other examples include the forested Puʻu Huluhulu, located near Maunaulu, and in the Kamakaiʻa Hills of the Kaʻū Desert.