A volcano is a vent in Earth’s surface from which lava, rock, ash, and hot gases erupt. Most volcanoes are located along the boundaries of tectonic plates, although some, such as those that built the Hawai’ian Islands, are found over hot spots. Scientists suspect that hot spots occur over mantle plumes.

Scientists use a variety of different classification systems to categorize volcanoes for study. This map layer classifies volcanoes as either composite, cinder cone, shield, fissure, caldera, or unknown types. Composite volcanoes, also called stratovolcanoes, are built by two types of eruption; lava flow and pyroclastic flow. Often the eruption begins with an explosion of ash and debris and ends with thick lava flows. The material from these eruptions builds up forming steep slopes with a crater at the top. One of Earth’s most famous volcanoes—Krakatau, located in Indonesia—is classified as a composite volcano.

Cinder cone volcanoes, sometimes called pyroclastic cones, are formed from the build-up of small, loose, pyroclastic debris. Since these hot fragments are small, they cool quickly as they erupt, which prevents them from sticking together. As a result in locations with high winds, the volcanic vent may be located upwind of the cone. An example of this type of volcano is Cerro Negro in Nicaragua.

Shield volcanoes, primarily composed of the igneous rock, basalt, are building over longer periods of time as layer after layer of lava flows and hardens. These appear to be dome-shaped mountains. One example of this type is Mauna Loa, in Hawai’i.

Fissure vents follow the paths of dikes (magma filled fractures in the rock). These dikes may run out the side of another type of volcano or along the ground near a rift zone where two plates are spreading. Iceland has a number of fissure vents as the island sits on two diverging plates, the North American Plate and the Eurasian Plate.

Caldera volcanoes, like Crater Lake in Oregon, United States, are large oval depressions formed by the collapse of the magma chamber after a previous eruption.

The United States Geologic Survey estimates that Earth is home to about 1,500 active volcanoes. Use this layer to explore the awesome force of nature shaping our landscape.


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Use this Map Layer in the Classroom

Tectonic Plates and Physical Features: In this activity, students will analyze maps of tectonic plates to predict the location of physical features.

active volcano
Noun

volcano that has had a recorded eruption since the last glacial period, about 10,000 years ago.

basalt
Noun

type of dark volcanic rock.

Noun

large depression resulting from the collapse of the center of a volcano.

cinder cone
Noun

hill created by tiny bits of lava blown out of a volcano and fallen down around the volcanic vent. Also called a scoria cone.

composite volcano
Noun

steep volcano made of hardened lava, rock, and ash. Also known as a stratovolcano.

Noun

bowl-shaped depression formed by a volcanic eruption or impact of a meteorite.

debris
Noun

remains of something broken or destroyed; waste, or garbage.

dormant volcano
Noun

volcano that has erupted in the past but is unlikely to erupt soon.

eruption
Noun

release of material from an opening in the Earth's crust.

extinct volcano
Noun

volcano that will no longer erupt.

fissure
Noun

narrow opening or crack.

Noun

intensely hot region deep within the Earth that rises to just underneath the surface. Some hot spots produce volcanoes.

Noun

rock formed by the cooling of magma or lava.

lava
Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

magma chamber
Noun

underground reservoir that holds molten rock.

Noun

middle layer of the Earth, made of mostly solid rock.

pyroclastic cone
Noun

hill created by tiny bits of lava blown out of a volcano and fallen down around the volcanic vent. Also called a cinder cone.

Noun

current of volcanic ash, lava, and gas that flows from a volcano.

shield volcano
Noun

large, gently sloping volcano made from fluid lava.

stratovolcano
Noun

steep volcano made of hardened lava, rock, and ash. Also known as a composite volcano.

tectonic plate
Noun

massive slab of solid rock made up of Earth's lithosphere (crust and upper mantle). Also called lithospheric plate.

vent
Noun

crack in the Earth's crust that spews hot gases and mineral-rich water.

Noun

an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.