Volcanic cone

Volcanic cones are some of the most recognizable landforms on Earth. They are created by ejecta, which are fragments of rock or lava thrown from a volcanic vent. As this material falls, it piles up around the vent. This process builds a cone shape with a central crater at the summit.

The specific type of cone that forms depends on the size and nature of the ejected fragments. Scientists categorize these landforms into several distinct types based on their composition and how they are built.

Stratocones, also called composite cones or Vesuvian-type volcanoes, are large and complex. They feature a steep profile and are built from alternating layers of lava flows and pyroclastic rocks. Pyroclastic rocks are materials moved by explosive eruptions. These volcanoes often have a central core of intrusive rocks. This core can be several kilometers in diameter.

Stratocones are typically andesitic to dacitic in composition. They are often found near subduction zones. Some large stratocones may even have calderas, which are large, collapsed craters.

Spatter cones are smaller, steep-sided mounds formed by lava fountains. These fountains issue highly fluid, mafic lava from a central vent. As blobs of molten lava, known as spatter, are thrown into the air, they do not cool completely. When they land, they are still soft, much like taffy. This causes the pieces to bind together through a process called welding.

This results in a cone made of agglutinated or welded spatter. If the lava comes from a linear fissure rather than a single vent, it creates long, wall-like features called spatter ramparts.

Tuff cones, or ash cones, are small, monogenetic volcanoes. They are produced by phreatic explosions, which are hydrovolcanic eruptions driven by steam. These occur when magma interacts with groundwater or surface water. This interaction produces fine-grained ash with the consistency of flour.

Tuff cones have steep slopes greater than 25 degrees and high rims. They are made of thick-bedded pyroclastic deposits. A related feature is the tuff ring. Tuff rings have much gentler slopes of 25 degrees or less. Their craters are often excavated below the ground surface, allowing them to fill with water and form lakes.

Cinder cones, also called scoria cones, are small and often very symmetrical. They are built from loose pyroclastic fragments like cinders, clinkers, or scoria. These fragments are created when gas-charged lava is blown violently into the air. The pieces solidify and fall around the vent, forming a cone with slopes between 30 and 40 degrees.

Most cinder cones have a bowl-shaped crater at the top. Their basal diameters average about 200 to 300 meters, though they can range from 100 to 600 meters. They rarely rise more than 300 meters above their surroundings.

Cinder cones are often monogenetic, meaning they typically erupt only once. Their eruptions are brief, lasting from a few days to a few years. In fact, 50% of observed eruptions last less than 30 days, and 95% stop within one year.

However, some can last longer; for example, Parícutin in Mexico erupted from 1943 to 1952. Because they are made of loose, unconsolidated debris, cinder cones tend to erode quickly once they become inactive. They are common in large basaltic volcanic fields and on the flanks of larger volcanoes.

Finally, some cones are classified as rootless cones, or pseudocraters. These are not connected to a deep magma reservoir by a conduit. Instead, they form when hot lava or pyroclastic flows interact with water on the surface. Littoral cones form when lava enters the sea or ocean. Explosion craters form when lava covers marshy or water-saturated ground. There are also hornitos, which are small cones of welded lava fragments. These form when gas and molten lava escape through cracks in a cooling lava flow.