Volcanic cones built of welded basaltic lava
Article by: Hobart M. King, PhD, RPG
What is a Spatter Cone?
A spatter cone is a small, steep-sided volcanic cone built up around a vent where escaping gases blow out chunks of molten lava. The chunks of molten lava are torn apart as they fly through the air and fall close to the vent before solidifying. Upon impact the still-molten lava welds to previously erupted material, building up a steep cone of "spatter", also known as "agglutinate".
Spatter cones are small, usually less than 30 feet tall, and circular in shape. They are a common feature where highly fluid basaltic magmas are erupted. A few spatter cones are built from carbonatite lava. Carbonatite is a rare igneous rock composed of carbonate minerals.
Cinder Cones vs Spatter Cones
Cinder cones and spatter cones are very similar features. But, here is the important difference: cinder cones are built up of loose clinkery materials (usually a rock named scoria) that you can easily pick up and examine. However, pieces of spatter are mostly welded together.
To examine a piece of spatter, you might need to break it free with a hammer. However, many spatter cones are in parks or other protected areas - where breaking up the rocks might get you in serious trouble. If that is the case, you would need to get as close as possible for a visual inspection.
Fissure Eruptions and Ramparts
Many spatter cones grow along fissures (fractures in the Earth where lava can erupt onto Earth's surface). If the fissure is erupting at only one or a few locations, then spatter cones might grow. However, if the entire fissure or sections of the fissure are erupting, a mound of spatter might accumulate on both sides of the fissure. This mound of spatter is known as a "rampart". A photo of an active fissure eruption building a rampart can be seen in the photo above from Hawaii's Kilauea volcano.
Hornitos are small mounds of spatter that usually form on the thin crust of a pahoehoe lava flow. They form where a small amount of lava escapes to the surface from a lava tube below. They are not considered to be a "volcano" because they are not connected to a true magma source at depth. Please see the accompanying photo.
Where are Spatter Cones?
Spatter cones and ramparts built by fissure eruptions have formed in many parts of the world. The list below contains some of the better-known locations where historic (inactive) spatter cones are present.
California, USA: a spatter cone vent at Fleener Chimneys (Lava Beds National Monument)
Canary Islands: Cumbre Vieja ridge, La Palma Island
Ecuador: Galapagos Islands
Hawaii, USA: Kilauea volcano (east rift zone and summit crater)
Iceland: Fagradalsfjall Volcano area
Idaho, USA: Craters of the Moon National Park
Reunion Island: in the Piton de la Fournaise caldera
Tanzania: carbonatite spatter cones in the Ol Doinyo Lengai volcano area
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