Igneous Rocks and Environments Flashcards

Vocabulary-style flashcards covering igneous rock composition, texture, magma evolution, and volcanic eruptive environments.

Magma

Molten rock stored beneath the Earth's surface under pressure, consisting of a mixture of melt, mineral crystals, and dissolved volatiles.

Lava

Molten rock that has erupted onto the Earth's surface and released its dissolved gases/volatiles due to the decrease in pressure.

Bowen's Reaction Series

A conceptual model illustrating that different silicate minerals in cooling magmas crystallize across a range of temperatures, from approximately $1300\,^\circ\text{C}$ down to $750\,^\circ\text{C}$.

Volcanic Rocks (Extrusive Igneous Rocks)

Igneous rocks formed from the rapid cooling and solidification of molten rock on the Earth's surface, including lava flows and pyroclasts.

Plutonic Rocks (Intrusive Igneous Rocks)

Igneous rocks formed from magma that slowly cools and solidifies beneath the Earth's surface.

Viscosity

A fluid's resistance to flow, often categorized in magmas as either high (sticky) or low (runny).

Porphyritic Texture

An igneous texture featuring larger, visible mineral crystals floating in a finer-grained matrix or groundmass.

Phenocryst

A large, distinct crystal embedded within a finer-grained matrix in a porphyritic igneous rock.

Aphanitic Texture

A fine-grained igneous rock texture where individual mineral crystals are too small to be visible to the naked eye.

Vesicular Texture

An igneous rock texture marked by small cavities or gas bubbles (vesicles) formed by escaping gases as lava cools.

Amygdaloidal Basalt

A vesicular basalt in which the former gas cavities (vesicles) have been filled in by secondary minerals.

Basalt Textures

The textural categories observed in basaltic rocks, including aphanitic, vesicular, amygdaloidal, and porphyritic textures.

Pumice

A felsic, highly vesicular extrusive igneous rock formed when gas-rich magma rapidly erupts and expands into a solidified volcanic foam.

Ash (Volcanic)

Very tiny glass particles of supercooled felsic magma produced during an explosive pyroclastic eruption.

Andesite

An intermediate extrusive igneous rock derived from sticky lava with moderate viscosity.

Stratovolcano (Composite Volcano)

A steep, symmetrical volcano built from alternating layers of pyroclastics and viscous lava flows, typical of subduction zone environments.

Shield Volcano

A broad volcano with low-angle slopes created by successive flows of low-viscosity, runny basaltic lava.

Cinder Cone

A small, steep volcano built around a single vent by ejected cinders, ash, and rock fragments during explosive spurts.

Types of Volcanoes

Major volcanic landforms categorized by shape and eruption style: shield volcanoes, composite volcanoes, lava domes, and cinder cones.

Monogenetic Volcano

A volcano formed during a single eruptive episode, a characteristic typical of many cinder cones.

Magma Evolution

The process by which the chemical composition of a magma body changes, occurring via differentiation, partial melting, assimilation, or magma mixing.

Plinian Eruption

A violent, highly explosive eruption driven by high-viscosity, gas-rich magma that launches rock and ash tens of miles into the atmosphere.

Hawaiian Fire Fountain

An eruption style where fluid, low-viscosity lava with high gas content is continuously sprayed upward like a geyser.

Lahar

A destructive volcanic mudflow composed of water, ash, and rock debris that travels down river valleys draining a volcano.

Skjaldbreiður

A shield volcano in Iceland formed at a divergent plate boundary through the accumulation of low-viscosity basaltic lava.

Lava Butte

A cinder cone in Oregon formed approximately $7000\,\text{years}$ ago as a parasitic vent to a larger shield volcano, composed primarily of scoria.