Volcanic cone
Volcanic cones are among the simplest
volcano formations. They are built by fragments (called
ejecta) thrown up (ejected) from a volcanic vent, piling up around the vent in the shape of a
cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption. Types typically differentiated are
spatter cone,
cinder cone,
ash cone, and
tuff cone.
- A spatter cone is formed of spatter: molten lava ejected from a vent. Expanding gases in the lava fountains tear the liquid rock into irregular gobs that fall back to earth, forming a heap around the vent. The still partly liquid rock splashed down and over the sides of the developing mound is called spatter. Because spatter is not fully solid when it lands, the individual deposits are very irregular in shape and weld together as they cool, and in this way particularly differ from cinder and ash. Spatter cones are typical of volcanoes with highly fluid magma, such as those found in the Hawaiian Islands.
- An ash cone is comprised of particles of silt to sand size. Explosive eruptions from a vent where the magma is interacting with groundwater or the sea (as in an eruption off the coast) produce steam and are called phreatic. The interaction between the magma, expanding steam, and volcanic gases results in the ejection of mostly small particles called ash. Fallen ash has the consistency of flour. The unconsolidated ash forms an ash cone which becomes a tuff cone (see tuff) once the ash consolidates.
An example of a tuff cone is
Diamond Head at
Waikīkī in
Hawai'i.
- A cinder cone is a volcanic cone built almost entirely of loose volcanic fragments called cinders (pumice, (pyroclastics, or tephra). They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit. Cinder cones rarely rise more than 300-500 m or so above their surroundings, and, being unconsolidated, tend to erode rapidly unless further eruptions occur. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world.
