Ash cloud (eruption column)A cloud of hot ash and rock fragments, many kilometers high. Volcanic gases carry it up.
CraterThe bowl-shaped hollow at the summit, round the central vent.
Main vent (central vent)The opening at the top of the conduit, in the crater floor. Magma comes out here.
Lava flowMagma that has reached the surface. It runs down the flank as lava.
Magma chamberA reservoir of molten magma in the crust that feeds the volcano.
Inside the volcano: 5 5
Conduit (pipe)The channel magma rises through from the chamber to the vent.
Side ventA branch from the conduit that erupts on the flank. Not from the summit. It can build a small parasitic cone.
Layers of lava and ashAlternating layers of lava, ash and cinders from many eruptions. A composite volcano is built of them.
DikeMagma that fills a crack cutting across the layers and hardens. Dikes strengthen the cone like ribs.
SillA flat sheet of magma that pushes in between layers. It runs along them rather than across.
How this list was compiled: Read 2026-09-26. (1) US Geological Survey, Principal Types of Volcanoes, https://pubs.usgs.gov/gip/volc/types.html : composite volcanoes (stratovolcanoes) are built of alternating layers of lava flows, ash, cinders, blocks and bombs; a crater at the summit holds a central vent; lava flows through breaks in the crater wall or from fissures on the flanks; lava solidified in fissures forms dikes that act as ribs strengthening the cone; a conduit system carries magma up from a reservoir in the crust. (2) Wikipedia, read the same day: Volcano (https://en.wikipedia.org/wiki/Volcano: magma chamber, conduit, vent), Sill (geology) (https://en.wikipedia.org/wiki/Sill_(geology): a sheet intruded between older layers, not across them), Eruption column (https://en.wikipedia.org/wiki/Eruption_column: a cloud of hot ash and tephra suspended in gases, rising many kilometres), Parasitic cone (https://en.wikipedia.org/wiki/Parasitic_cone: a cone from eruptions on the flank, not the central vent). Licence: own work
The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work
How it works
The parts of a volcano on one composite volcano cut in half. Start with the 5 main parts you can see from outside or deep below, then the 5 inside the cone. Quiz me hides the names, so it doubles as a blank worksheet.
Read the full guide
From the chamber up
Magma collects in a magma chamber in the crust. It rises through the conduit to the main vent in the crater at the summit, and erupts as lava flows and an ash cloud. A side vent is a branch that erupts on the flank.
Inside the cone
A composite volcano, or stratovolcano, is built of alternating layers of lava and ash from many eruptions. Magma that hardens in a crack cutting across the layers is a dike; a flat sheet pushed in between layers is a sill.
Dike or sill? A dike cuts across the layers; a sill runs along them.
Questions and answers
What are the main parts of a volcano?
The magma chamber, the conduit (or pipe), the main vent, the crater, and what comes out: lava flows and an ash cloud. Many volcanoes also have side vents.
What is the difference between magma and lava?
Magma is molten rock underground. Once it reaches the surface it is called lava.
What is a composite volcano?
A steep, cone-shaped volcano built of alternating layers of lava flows, ash and cinders, such as Mount Fuji or Mount St. Helens. It is also called a stratovolcano.