Chapter 6: Volcanoes and Igneous rocks

Terms in this set (53)

An igneous rock texture with mineral grains so small they can be observed only under a magnifying lens

A large, irregularly shaped pluton that cuts across the layering of the rock into which it intrudes

Crystallization

The process whereby mineral grains form and grow in a cooling magma (or lava)

Fractional crystallization

Separation of crystals from liquids during crystallization

Fractional melt

A mixture of molten and solid rock

Separation of melted materials from the remaining solid material in the course of melting

Molten rock that reaches the earths surface

Molten rock that may include fragments of rock, volcanic glass and ash, or gas

an igneous rock texture with mineral grains large enough to be seen by the unaided eye

Any body of intrusive igneous rock, regardless of size or shape

Igneous rock that solidifies underground, from magma

Pyroclastic flow

Hot volcanic fragments (tephra) that flow very rapidly, buoyed by heat and volcanic gases. The most dangerous consequence of a volcanic eruption. Associated with Vulcanian eruptions

A broad, flat volcano with gently sloping sides, built of successive lava flows, usually caused by flows of very low viscosity lava (low silica). ie. Iceland, Hawaii

A volcano composed of solidified lava flows interlayered with pyroclastic material. Such volcanoes usually have steep sides that curve upward. Caused by explosive vulcanian and Plinian eruptions.

The degree to which a substance resists flow; a less viscous liquid is runny, where as a more viscous liquid is thick. Causes the diversity of eruption types. Low viscosity is runny lava, high viscosity is thicker. more silica = higher viscosity

Igneous rock that solidifies on or near the surface, from lava

A vent through which lava, solid rock debris, volcanic ash, and gases erupt from Earth's crust to its surface

A fragment of rock ejected during volcanic eruption

All the ejecta from a volcano is known collectively as this

Ultrafine matter ejected from a volcano, individual particles can be seen only under microscope

Strombolian eruptions

Explosive eruptions that may eject showers of lava or pyroclasts hundreds of feet in the air. This type of eruption creates cones of loose volcanic rock called spatter cones, tephra cones, or cinder cone

When tephra particles are large

When tephra particles are small

Eruptions that are more explosive than Strombolian; they propel billowing clouds of ash to a height of 10 km. They also produce pyroclastic flows of hot cinders and ash that sweep down the mountainside like an avalanche

Near the summit of most volcanoes this is a funnel shaped depression from which gas, tephra, and lava are ejected

When groundwater comes in contact with hot rock surrounding the magma chamber

Intermittent eruptions of water and steam; means to gush. ie. Iceland

When a volcanic vent emits only gas- usually water vapor that is sometimes mixed with foul-smelling sulfur compounds

Primary effects

Effects directly caused by the eruption. Lava flows, and the more dangerous pyroclastic flows

Secondary effects

Effects indirectly triggered by the eruption. Volcanic tremors (seismic activity), lahars (deadly mudflow), debris avalanche

Tertiary effects

Long-lasting or permanent changes brought about by eruptions. Aerosols (small droplets of sulfur dioxide that absorb sunlight and cool the earth's surface)

A volcano that has erupted within recorded history

Dormant volcano

A volcano that has not erupted in recent history

Extinct volcano

A volcano that shows no signs of activity and is deeply eroded

A reservoir of magma lying underneath an active volcano

Geothermal gradient

The rate at which temperatures increase. In the continental crust, temperatures rise initially at about 30°C per kilometre

Igneous rocks which consist of a texture of large mineral grains embedded in aphenitic matrix. Magma cooling at a depth and then quickly being ejected before fully crystallizing

Dissolved gases affect the texture of volcanic rock; froth that is blasted into the air cools quickly and forms this type of rock which is a glassy mass full of bubbles (vesicles).

A rock with lots of bubbles it resembles Swiss cheese; this happens when the lava solidifies and traps gas

Rock that contains a large amount of silica, about 70%, and is usually light-colored. ie Feldspar, Rhyolite, Granite

A rock with a large amount of dark-colored minerals rich in magnesium and iron; it is usually lower in silica content 50%. ie. Gabbro, Basalt

An igneous rock that contains roughly 60% silica and is intermediate and both composition and colour

A volcanic rock with small grain size and high silica content (Felsic), consists of quartz and feldspar

Plutonic equivalent of rhyolite, large grain size and high silica content (Felsic)

An intermediate silica rock, with lots of feldspar mixed with darker magic minerals. Volcanic rock

Plutonic equivalent of andesite, an intermediate silica rock

Mafic rock dominant in the Oceanic crust, the most common igneous rock on earth, large volume, low viscosity lava flows from shield volcanoes and fissures are usually made of this.

The plutonic equivalent of basalt, a low silica rock

A smaller version of a batholith, only 10 km or so at its maximum dimension

Forms when magma squeezes into a cross cutting fracture and then solidifies

Forms when magma intrudes between two layers and is parallel to them. Sometimes causes the overlying rock to bulge upward, forming a mushroom shaped pluton called a laccolith

The remnant of a channel that originally fed magma to the volcanic vent

A volcanic pipe exposed by erosion

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