Cinder cones are the simplest type of volcano. 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 and rarely rise more than a thousand feet or so above their
surroundings. Cinder cones are numerous in western North America as well
as throughout other volcanic terrains of the world.
[Illustration: Schematic representation of the internal structure of a
typical cinder cone.]
In 1943 a cinder cone started growing on a farm near the village of
Parícutin in Mexico. Explosive eruptions caused by gas rapidly expanding
and escaping from molten lava formed cinders that fell back around the
vent, building up the cone to a height of 1,200 feet. The last explosive
eruption left a funnel-shaped crater at the top of the cone. After the
excess gases had largely dissipated, the molten rock quietly poured out
on the surrounding surface of the cone and moved downslope as lava
flows. This order of events—eruption, formation of cone and crater, lava
flow—is a common sequence in the formation of cinder cones.
[Illustration: Parícutin Volcano, Mexico, is a cinder cone rising
approximately 1,200 feet above the surrounding plain.]
During 9 years of activity, Parícutin built a prominent cone, covered
about 100 square miles with ashes, and destroyed the town of San Juan.
Geologists from many parts of the world studied Parícutin during its
lifetime and learned a great deal about volcanism, its products, and the
modification of a volcanic landform by erosion.