Volcanoes, Volcanism, and Igneous Rocks

a'a

A lava flow of basaltic lava that forms rough, jagged blocks. It forms when the lava has cooled down, thus increasing the viscosity.

andesitic magma (intermediate)

magma that is a mix of basaltic and rhyolitic; eruption may or may not be explosive

ash

Tephra less than 2mm in diameter

basaltic magma (mafic)

magma that has low viscosity and low silica and gas content; eruption is non-explosive

Batholiths

A very large intrusive igneous rock mass that has been exposed by erosion and with an exposed surface area of over 100 square kilometers.

Caldera

a large crater caused by the violent explosion of a volcano that collapses into a depression

cinder cone volcano

Volcanos built from ejected lava fragments (pyroclastic material). A product of relatively gas-rich mafic magma. They are very steep, have deep craters, and do not usually eject lava. 1000-1500 ft (small), mild eruptions, example : Paricutin, Mexico

Clinkers

broken lava blocks that fall down the from of an Aa flow

coarse-grained

Large crystals, formed from igneous rock which cooled slowly. Nerd-sized

concordant

A descriptive word for plutons that form parallel to features such as sedimentary strata.

convergent boundary

the volcanic setting when water is dragged down by a plate and causes the mantle to partially melt, magma slowly rises up and forms volcanic island arc and continental volcanic rock. It contains felsic rocks and has more violent eruptions

crystallization

The process by which magma cools and solidifies. This may occur beneath the surface or after a volcanic eruption. The slower the process, the larger the crystals.

dike

Tabular discordant plutons that are produced when magma is injected into fractures.

discordant

A descriptive word for plutons that are cut across existing structures.

divergent boundaries

(type of boundary) greatest volume of volcanic rock is produced along the oceanic ridge, lithosphere pulls apart, less pressure on underlying rock, on land causes a rift

extrusive (volcanic)

rocks that form when molten rock solidify at the surface,

felsic

light in color, high in quartz and feldspar, generated by partial melting at subduction boundaries

fine-grained

The texture of igneous rocks that form rapidly at the surface. Crystals are thus too small to be seen.

glassy

The texture of igneous rocks that cool too quickly to form crystals.

hornito

A small, steep sided spatter cone that forms on the surface of a lava flow (usually pahoehoe)

Hot Spot

an area where material from deep within the mantle rises and then melts, forming magma

igneous rock

the rock resulting from the cooling and crystallized magma or lava

intermediate

rock that has roughly even mixtures of felsic and mafic minerals

intrusive (plutonic)

igneous rocks that form at depth that are only exposed through uplifting.

Kipuka

A small piece of land that is completely surrounded by lava flows

laccoliths

Tabular concordant plutons that form when viscous magma is injected between sedimentary layers near the surface. It is dome-shaped.

lahar

Large composite cones generate this type of mudflow, which is saturated volcanic debris that moves down the steep volcano slopes. They can form in hard rainfall or when the volcano erupts and melts snow

lapilli

Tephra between 2mm-64mm in diameter and is vesicular

lava

hot molten (or semi molten) rock that has reached the surface. Most of the gasses have escaped

lava bench

a platform formed by new lava flows that extends the old shoreline, making new land

lava block

Tephra that is bigger than 64mm, solid piece of side of volcano

lava bombs

Ejected from a volcano while molten or semi-molten

lava lake

a pool of molten lava that has collected in a caldera

Lava mold

Type of lava formation that is formed when lava surounds a tree, clings against it and drains away

lava trees

Lava surrounds the tree but does not destroy it (leaves a column of rock.)

Lava tubes

A natural conduit where lava travels under the surface of a lava flow. The tubes form by the crusting over of lava channels. (generally pahoehoe lava)

mafic

igneous rocks high in Mg and Fe, dark colored, prevalent in ocean crust

magma

hot , molten rock located under ground made of a liquid (melt), solid portion (minerals)

magma chamber

the body of molten rock that feeds a volcano

Pahoehoe

a hot, fast-moving type of lava that hardens to form smooth, ropelike coils

Pele

Hawaiian goddess of the Volcanoes

Pele's Hair

A naturally spun volcanic glass thats blown away from lava formations, lava falls, or turbulent flows. Generally gold in color

pele's tears

molten lava spews up and as it falls down, it's elongated

pillow basalt

Pluton

Intrusive igneous rock bodies, including batholiths, stocks, sills, and dikes, formed through mountain-building processes and oceanic-oceanic collisions; can be exposed at Earth's surface due to uplift and erosion.

pyroclastics (tephra)

A general term for fragments of volcanic rock and lava that are blasted into the air (solid.)

Pyroclastic flow

a ground- hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the Mt. 100-400 mph, deadliest aspect of a volcanic eruption and can reach temperatures of 600-800 degrees

rhyolitic magma (felsic)

magma that has a high viscosity and high silica and gas content; eruption tends to be very explosive

rift eruption (curtain of fire)

Tall explosions of lava from fissures found on land at divergent plate boundaries.

Ring of Fire

A narrow zone that rims the Pacific Ocean and contains most of the active continental volcanoes (composite cones.)

shield volcanoes

Broad, slightly domed volcanoes. They are formed by fluid basaltic lavas and are frown up from the ocean floor to form islands or seamounts. (An example is the Hawaiian chain.)

silica

a material found in magma that is formed from the elements oxygen and silicon

sill

tabular and concordant plutons form when magma is injected along sedimentary bedding surfaces, horizontal, uniformly thick

skylight

an opening in the roof of a lava tube

stock

smaller batholith that is less than 100m2 above the surface

Stratovolcano (Composite Volcano)

classic volcanic shape, taller than wide, layers, Made from felsic magma, high in quartz, high in viscosity, high in gas content, violent eruptions, Example: Mt. St. Helens, Fuji, Tambora

texture

appearance of an igneous rock based on the size, shape, and arrangement of crystals

Tsunami

Japanese word for "harbor wave", a volcanic eruptions abruptly displaces ocean water by either an explosion or landslide, Example : Krakatoa

very-coarse grained (pegmatitic)

Mineral grains that are exceptionally large. The largest ones can be more than 3 cm long.

vesicular

igneous rock texture that has air bubbles, large minerals, and forms with aa

viscosity

a magmas resistance to flow, factors including temp and magmas chemical composition

Volcanic Explosivity Index (VEI)

An intensity scale that rates a volcano's destructiveness and explosive power on the amount of matter it ejects during an eruption.

Volcanic Fissure

the eruption of magma out of a crack in the lithosphere, rather than from a single pipe or vent

Volcanic Neck

a deposit of hardened magma in a volcano's pipe

volcanic pipe

the conduit connecting the crater of a volcano with an underlying magma chamber

Volcanism

the activity of magma forming and coming toward surface

Volcano

landform created when magma reaches the surface through an opening in Earth's crust

xenolith

when a different type of rock is incorporated into another plutonic rock