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Chapter 6: Volcanoes and Igneous rocks
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Terms in this set (53)
Aphanitic
An igneous rock texture with mineral grains so small they can be observed only under a magnifying lens
Batholith
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
Fractionation
Separation of melted materials from the remaining solid material in the course of melting
Lava
Molten rock that reaches the earths surface
Magma
Molten rock that may include fragments of rock, volcanic glass and ash, or gas
Phaneritic
an igneous rock texture with mineral grains large enough to be seen by the unaided eye
Pluton
Any body of intrusive igneous rock, regardless of size or shape
Plutonic rock
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
Shield volcano
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
Stratovolcano
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.
Viscosity
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
Volcanic rock
Igneous rock that solidifies on or near the surface, from lava
Volcano
A vent through which lava, solid rock debris, volcanic ash, and gases erupt from Earth's crust to its surface
Pyroclast
A fragment of rock ejected during volcanic eruption
tephra
All the ejecta from a volcano is known collectively as this
Volcanic ash
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
Agglomerate
When tephra particles are large
Tuff
When tephra particles are small
Vulcanian
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
Crater
Near the summit of most volcanoes this is a funnel shaped depression from which gas, tephra, and lava are ejected
Thermal spring
When groundwater comes in contact with hot rock surrounding the magma chamber
Geyser
Intermittent eruptions of water and steam; means to gush. ie. Iceland
Fumaroles
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)
Active volcano
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
Magma chamber
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
Porphyritic
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
Pumice
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).
Vesicular
A rock with lots of bubbles it resembles Swiss cheese; this happens when the lava solidifies and traps gas
Felsic
Rock that contains a large amount of silica, about 70%, and is usually light-colored. ie Feldspar, Rhyolite, Granite
Mafic
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
Intermediate
An igneous rock that contains roughly 60% silica and is intermediate and both composition and colour
Rhyolite
A volcanic rock with small grain size and high silica content (Felsic), consists of quartz and feldspar
Granite
Plutonic equivalent of rhyolite, large grain size and high silica content (Felsic)
Andesite
An intermediate silica rock, with lots of feldspar mixed with darker magic minerals. Volcanic rock
Diorite
Plutonic equivalent of andesite, an intermediate silica rock
Basalt
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.
Gabro
The plutonic equivalent of basalt, a low silica rock
Stock
A smaller version of a batholith, only 10 km or so at its maximum dimension
Dike
Forms when magma squeezes into a cross cutting fracture and then solidifies
Sill
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
Volcanic pipe
The remnant of a channel that originally fed magma to the volcanic vent
Volcanic neck
A volcanic pipe exposed by erosion
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