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USGS Geology in the Parks

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Lava flow trail stop 7

Miniature Volcanoes

A hornito along the Bonito Lava Flow trail
One of the largest hornitos along the Bonito Lava Flow trail.

Picture a kettle of hot, bubbling spaghetti sauce. In your imagination, can you see the bubbles rise to the surface, then spatter blobs of red sauce in a ring around the bubbles? That's the process that formed these spatter cones or hornitos ('little ovens' in Spanish) on the surface of Bonito Lava Flow.

Close-up of gloppy spatter texture
This mound was formed by glob after glob of lava falling along the edge of a spatter cone.

One to fifteen meter (3-50 feet) high spatter cones form a string of lumpy beads along a once-active vent system near the base of Sunset Crater Volcano. Like bubbling spaghetti sauce, they form when gasses escape from molten lava beneath the crusty, solid surface of a flow.

If you look closely at this spatter cone you can easily see where individual 'spatters' fell with a SPLAT! onto the ring of solidified lava. Their heat welded them to the older spatters, gradually building the miniature volcanoes you see here.

TAKE A SIDE TRIP: Spatter cone in action

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