Volcanoes

tephra

Solid and molten rock fragments

bombs

largest ejected rock fragments

ash

Small fragments of glass, minerals, and rock

Volcanic gas emissions

More than 90% of all gas emitted by volcanoes is water vapor (steam), most of which is heated ground water (underground water from rainfall and streams). Other common volcanic gases are carbon dioxide, sulfur dioxide, hydrogen sulfide, hydrogen, and fluorine.

magma

molten rock

andesite and dacite lava

Low silica, thick lava, unlike Basalt

pyroclastic flows

fast-moving currents of hot gas and volcanic matter that flow down the slopes of a volcano during an explosive eruption.

Lahars

Mudflows or debris flows composed mostly of volcanic materials on the flanks of a volcano

Intrusive/plutonic rocks

Form when magma cools underground (granite)

Tuff

Rock composed of tephra

pumice

Froth formed from separated gas from lava

Basalt

Darkest colored volcanic rock. Commonly found at oceanic and continental hot spots. Low silica content. Rarely part of explosive eruptions, can be rusty red from corrosive gases.

Andesite

medium-gray and intermediate colors, found primarily at convergent plate boundaries. Intermediate silica content.

Rhyolite

Lightest colored volcanic rock, can be found at continental hot spots, high silica content, tuff is common, from highly explosive eruptions, often contains pumice.

Cooling joints

Fractures formed because, as lava cools and hardens, it contracts. To accommodate the decreased volume these open, breaking the lava into 6-sided columns.

Four main types of volcanoes

Cinder cones, composite volcanoes, shield volcanoes, and lava domes.

calderas

depressions formed by the collapse of volcanoes

Strombolian-type eruption

Highly explosive, high clots of magma burst from the crater.

Vulcanian-type eruption

Explosion creating a dense cloud of ash-laden gas.

Plinian eruption

Most powerful eruptions (pompeii) that create mushroom clouds of gas that can enter the stratosphere.

"Hawaiian" eruptions

Occur along fissures and fractures