Spatter cones are small, steep-sided, nearly circular conical hills or mounds of welded magma blobs or fragments formed around a vent.
These welded lava blobs or chunks are called spatter. They form when lava is ejected a short distance into the air and falls back into the ground while still plastic or semi-molten. Upon landing, it will weld together.
Spatter cones represent some of the smallest volcanic and eruptive landforms or features. They result from minor volcanic activities that involve highly fluid lavas, usually basaltic or carbonatitic.
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Composition
Spatter cones are mostly formed from highly fluid basaltic lavas. However, they can also develop from carbonatitic lavas.
Basaltic lavas are mafic lavas. Mafic means they are relatively low in silica and high in dark-colored minerals that contain iron and magnesium.
Such lavas are low in viscosity due to the lower silica content. Viscosity is the resistance to flow.
On the other hand, carbonatite lavas have more than 50% carbonates carbonate minerals. They are also relatively low in silica, with low viscosity.
Appearance and description
Spatter cones are small, steep to nearly vertical-sided hills or mounds. They are made of welded lava fragments and are roughly circular and symmetrical around vents.
However, some of these volcanic cones may be asymmetrical or one-sided. Such will form when wind or obstruction causes ejecta deflection. Ejecta is the material thrown into the air during an explosive eruption.
Usually, they have steep slopes because the partial cooling of lava during flight makes these lava blobs viscous or thick. Thus, they will stick to each other when they fall and not flow or roll.
How big are they? Spatter cones are usually less than 10 meters (33 feet) in height and less than 100 meters (330 meters in diameter).
However, some can be larger. For instance, the combined Pu’u ‘Ō’ō is a cinder and spatter cone in Kilauea’s east rift is 250 meters (820 feet) high.
On the landscape, they may appear alone on vent summits or in groups, linearly dotted along a fissure. Fissures are cracks or fractures from where the magma from the interior of Earth the source erupts.
Lastly, lava may overflow, forming a channel. Such channels will distort the conical shape.
How do spatter cones form?
They form during less intense volcanic eruptions of mafic or highly fluid lavas with considerable volatiles or gases.
Such eruptions will form lava fountains. Lava fountains form when escaping and expanding gas blows lava jets and blobs/chunks into the air.
The ejected lava blobs are torn while in flight and fall close to the vent before fully solidifying. Upon landing or impact, they will weld to previously erupted material. As more accumulate, it forms spatter cones and agglutinates around the vents.
Usually, these volcanic landforms occur around a central vent. However, they can also form on fissures with discrete eruptive points.
Those that form along the entire fissure are known as spatter ramparts.
What are spatter ramparts?
Spatter ramparts are small, steep-sided, elongated, ridge or wall-like volcanic landforms along fissures made of piles of splatter.
However, unlike spatter cones, which are circular, discrete mounds around a vent, ramparts are linear or wall-like and occur on either side of fissures.
Also, splatter ramparts are usually smaller, 1-5 meters (3-16 ft) high, and form from lava fountains less than 10 meters (33 feet) high.
Agglutinate or volcanello
Agglutinate describes a small spatter cone about 4-5 meters (13-16 feet) tall with mainly fused lava bomb pyroclasts. Pyroclasts are fragments ejected during an explosive volcanic eruption.
Agglutinates are also steep sides and occur around a fissure or vent and in spatter cones.
Where are they found?
Examples of places where spatter cones occur include Bartholomew Island in the Galapagos, Kīlauea Volcano in Hawaii, USA, and Fagradalsfjall Volcano in Southwest Iceland.
Also, they occur in Cumbre Vieja Ridge and La Palma Island in the Canary Islands, Craters of the Moon National Park in Idaho, USA, and Piton de la Fournaise Caldera in Reunion Island.
Lastly, Tanzania’s Ol Doinyo Lengai volcano has carbonatite spatter cones.
Spatter cones vs. cinder cones
Spatter cone volcanoes have welded lava fragments, mainly volcanic bombs, while cinder or scoria cones mainly have loose pea-sized to fist-sized, highly vesiculated fragments. However, scoria cones can have other fragments, too, including ash, lapilli, and blocks.
Also, they form from less intense eruptions that cinder cones where larger lava blobs don’t go far. Such will remain semi-molted when they land, making them weld.
On the other hand, cinder cones form from more intense eruptions that are richer in gases. The gases cause lava blobs to become vesiculated and cool before landing. Thus, they don’t weld together.
However, some eruptions may alternate between cinder and spatter, forming spatter-and-cinder cones.
Frequently asked questions
They form during mild to moderate Hawaiian or strombolian eruptions of highly fluid mafic magmas with considerable gases. These eruptions result in lava fountains.
Hornitos are small mounds made of spatter or welded lava fragments. They form when lava escapes from lava tubes in pahoehoe lava flows. Thus, they are not volcanic eruptive landforms as they don’t form from fissures or vents connected to magma sources deep inside the Earth, i.e., lack a root.