Anatomy of a Volcano

photo of glowing lava eruption in a large volcanic crater
Hawaiʻi Volcanoes National Park, Hawai'i.

NPS photo.

Introduction

Volcanoes are both the vents where molten rock material and volcanic gases are erupted from within Earth’s interior, and the cones and mountains built up around those vents. But beyond this simple definition, volcanoes are incredibly diverse with some types being very complex.

Some volcanoes make up the largest mountains on the planet, while others are small hills that may only be a few hundred feet (meters) tall. Some volcanoes erupt multiple times over periods of hundreds of thousands of years, while others experience a single eruptive episode.

Vents, the openings at the surface where volcanic eruptions occur, and conduits, the channelways that lead from the magma reservoir to the vent, are the only features that all volcanoes have. Some types of volcanoes are exclusively made up of deposits of volcanic ash and other types of tephra. Others are nearly wholly made of lava flows. And yet others contain both pyroclastic deposits and lava flows, and possibly also lava domes, lahar, and/or landslide deposits.

Depending on how they are grouped or subdivided, there are eight different types of volcanoes based on their size, shape, eruption style and classification, and types (composition) of magma erupted. Three types of volcanoes—cinder cones, composite volcanoes, and shield volcanoes—are the most common and are the best known. But examples of all eight types of volcanoes are found in national parks.

This page explores the anatomy (the internal and external structure) of cinder cones, compositive volcanoes, and shield volcanoes, and provides short introductions to the other five types of volcanoes.

Glossary—All Volcanoes


Cinder Cone Volcanoes

Cinder cones are small volcanoes that consist of volcanic ash, cinders, and other types of tephra that has piled up around a vent. Cinder cones are typically built in a single eruptive period that lasts a few months and that may include the eruption of fluid lava flows from vents located along the base. Cinder cones are usually less than 1,000 feet tall (330 m).

diagram of a volcano with cut-away to show interior. diagram of a volcano with cut-away to show interior.

Left image
Schematic diagram of a composite volcano.
Credit: NPS illustration by Trista Thornberry-Ehrlich (Colorado State University).

Right image
Diagram with feature labels.
Credit: NPS illustration by Trista Thornberry-Ehrlich (Colorado State University).

Glossary—Cinder Cone Volcanoes

Cinder cones are the most common type of volcano in the National Park System. At least 24 units in the National Park System contain cinder cones.

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Composite Volcanoes

Composite volcanoes experience many eruptive periods over a long expanse of time (hundreds of thousands of years). These complex volcanoes are made of lava flows, pyroclastic deposits, as well as volcanic domes. Lahars and landslides that reshape these volcanoes may occur during eruptions or at other times. This volcano type is also known as a stratovolcano, but the term "composite volcano" is generally preferred.

diagram of a volcano with cut-away to show interior. diagram of a volcano with cut-away to show interior.

Left image
Schematic diagram of a composite volcano.
Credit: Modified from USGS illustration.

Right image
Diagram with feature labels.
Credit: Modified from USGS illustration.

Glossary—Composite Volcanoes

At least eight units of the National Park System contain composite volcanoes.

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Shield Volcanoes

Shield volcanoes are almost exclusively made up of fluid lava flows that can travel great distances from their vents. Shields are massive volcanoes with gentle slopes. Eruptions are usually effusive and may occur at the summit area and along fissures located along their flanks. These volcanoes are characterized by numerous lava flows, lava flow fields, as well as surface features of basaltic lava flows. Shield volcanoes experience many eruptions over their lifespans.

illustration of a shield volcano showing several lava features illustration of a shield volcano showing several lava features

Left image
Schematic diagram of a shield volcano.
Credit: USGS illustration.

Right image
Diagram with feature labels.
Credit: USGS illustration.

Glossary—Shield Volcanoes

At least 13 units in the National Park System contain shield volcanoes.

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Volcanoes of Many Sizes

Volcanoes may be of any size. At the two ends of the size spectrum, cinder cones are typically the size of small hillocks and shield volcanoes may be the most massive mountains on Earth.

The difference in size between these two types of volcanoes is so vast that it is difficult to show their relative sizes in a single illustration. Shield volcanoes may be 30 or more times taller than cinder cones, and may have a volume of 25,000 times that of a cinder cone.

illustration comparing 3 volcano types (from largest to smallest) Mauna Loa shield volcano, Mt. Rainier composite volcano, Capulin Volcano Cinder Cone
An illustration of the difference in size between shield (Mauna Loa, Hawaii), composite (Mt. Rainier, Washington), and cinder cone (Capulin Volcano, New Mexico) volcanoes.

NPS illustration by Trista Thornberry-Ehrlich (Colorado State University).

Comparing The Three Classic Types of Volcanoes

Type

Size

Lifespan

Cinder Cone

Small
(<1,000 ft; 330 m tall)

Short (single eruption of a few months)

Composite Volcano

Large
(usually between 6,500 and 20,000 ft; 2,000-3,000 m tall)

Long (hundreds of thousands of years)

Shield Volcano

Very large
(up to a maximum of 33,000 ft; 10,000 m tall)

Very long
(up to a million years or longer)










Other Types of Volcanoes

These volcanoes frequently do not have the classical cone or shield shapes that many people ascribe to volcanic landforms. They include large features that may not at first appear to be a volcano, depressions that may be filled by lakes, and elongated vents where eruptions occur but where volcanic mountains are not constructed. Together, these types are an important part of the diversity of volcanoes. They also share many of the features of the three main types of volcanoes described above.

► Calderas

Calderas are large, roughly circular collapse features that form during voluminous eruptions that partially empty underlying magma chambers. Explosive calderas form during Volcanic Explosivity Index (VEI) 6–8 (Colossal to Apocalyptic) eruptions. Summit calderas form during climatic eruptions of preexisting composite volcanoes and may be more than 10 miles (16 km) in diameter. Resurgent calderas are even larger, with diameters of many tens of miles (kms).

illustration showing a caldera-forming eruption with cut away view of upper layers of the Earth, faults, magma and ash clouds
The caldera-forming eruption evacuates a significant amount of magma from the chamber, causing the overlying crustal block to subside into the void space.

USGS public domain image.

At least eight units of the National Park System contain calderas.

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► Volcanic Domes (Lava Domes)

Volcanic domes are steep-sided accumulations of highly viscous lavas that dome up after eruption from a vent instead of flowing laterally to form a lava flow.

Illustration showing a cut away view of a lava dome and its magma conduit
Illustration showing a cut away view of a lava dome and its magma conduit.

NPS illustration by Trista Thornberry-Ehrlich (Colorado State University).

At least 12 units of the National Park System contain volcanic domes.

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► Fissure Volcanoes

Volcanoes that have an elongated fissure as their vent. Some fissure volcanoes lack substantial edifices as they may erupt fluid lava flows that may travel great distances from the vent.

A block diagram of a volcanic dike showing features above and below the ground surface. Below the surface, a large vertical magma body is shown and at the surface, the magma feeds linear fissure vents.
Diagram showing the origin of fissure volcanoes from dikes intersecting the surface and feeding lava flows.

Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Hughes and others (1999) -- Mafic Volcanism and Environmental Geology of the Eastern Snake River Plain.

At least four units of the National Park System contain fissure volcanoes.

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► Maars and tuff rings

Maars and tuff rings form during highly explosive eruptions when hot magma interacts with water. Both types of volcanoes consist of low rings of tephra surrounding a central crater. Maars have craters below the general surface elevation and result from the interaction of magma with shallow groundwater or permafrost. Tuff rings have craters above the surrounding ground surface and form when eruptions encounter surface water or ice.

illustration of a maar explosion
Schematic illustration of a maar explosion. During phreatomagmatic eruptions, surface or groundwater interacts with hot magma, shattering pre-existing bedrock and fragmenting fresh magma in violent eruptions. These eruptions form small eruption columns and send out base surges.

NPS illustration by Trista L. Thornberry-Ehrlich (Colorado State University).

At least six units of the National Park System contain maars or tuff rings.

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► Monogenetic Volcanic Fields

Monogenetic volcanic fields may consist of hundreds of volcanic vents and associated lava flows and form in areas with low magma supply. Individual volcanoes in these fields, whether they are cinder cones, maars, tuff rings, fissure volcanoes or other types, each have their own volcanic plumbing system.

3d image of a volcanic landscape with lava flows in the foreground and peaks in the distance
The San Francisco Volcanic Field in northern Arizona. This monogenetic volcanic field contains a large eroded composite volcano in the center, some volcanic domes, but mostly cinder cone volcanoes. Sunset Crater Volcano NM contains one of the small cinder cones in the middle right of the image.

ASTER satellite image draped over USGS topographic data.

At least 13 units of the National Park system contain all or parts of monogenetic volcanic fields.

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Educational Slide Set—Volcano Illustrations

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Last updated: July 5, 2023