Magma Basics
This is the term for gases dissolved in magma that are released when pressure drops, like CO₂ in a soda bottle.
Volatile
This type of eruption is driven by easily escaping gases is typical of low-silica, fluid magmas.
Effusive
This light-colored, highly vesicular rock comes from silica-rich magma and can float on water.
Pumice
This steep-sided cone is built primarily from ejected lava fragments that harden in flight.
Cinder cone
This mushroom-shaped intrusive body domes up the overlying rock layers.
Laccolith
This felsic rock composed of light silicates results from melting of the continental crust.
Granite
This eruption is produced by the reduction of confining pressure, which evaporates gases and forms bubbles.
Explosive
This jagged, blocky basaltic lava flow is less fluid than its smoother counterpart.
This is the small funnel-shaped depression at the top of a volcanic cone
Crater
Tabular plutons that cut across existing rock layers are described by this term.
Discordant
This type of magma forms at higher temperatures
Basaltic
This towering cloud of hot ash and gases rises high above violently erupting volcanoes.
Eruption Column
Ejected, pulverized rock fragments are collectively known by this term
Tephra
This broad, gently sloping volcano type often begins life as a submarine seamount.
Shield Volcano
This concordant, sheet-like intrusive body runs parallel to the bedding of the surrounding rock.
Sill
This mafic rock composed of dark silicates results from partial melting of the upper mantle.
Basalt
This type of eruption is a gentle outpouring of lava, also known as quiescent.
Effusive
This smooth-surfaced basaltic lava flow is hotter and more fluid.
Pahoehoe
This is the top opening of a volcano.
Vent
This is subterranean crystallized igneous rock.
Pluton
Granitic magmas have high content of this substance, leading to greater viscosity.
Silica
In explosive eruptions, gases do this to the rock, reducing confining pressure and creating a runaway fragmentation.
Expand and Break
This bulbous lava formation develops when magma extrudes and quickly freezes underwater.
Pillow Lava
This volcanic depression is larger than 1 km in diameter and often forms by collapse.
Caldera
This discordant, sheet-like pluton runs perpendicular to the bedding of the surrounding rock.
Dike