GEO101 Exam 2 Terms & Practice Questions

The sequence in which different silicate minerals crystallize during the progressive cooling of a melt.

Bowen's reaction series

Rock formed by the freezing of magma underground.

intrusive igneous rock

A blister-shaped igneous intrusion that forms when magma injects between layers underground in a manner that pushes overlying layers upward to form a dome.

laccolith

A thick slurry formed when volcanic ash and debris mix with water, either in rivers or from rain or melting snow and ice on the flank of a volcano.

lahar

Tiny glass shards formed when a fine spray of exploded lava freezes instantly upon contact with the atmosphere

ash

A volcano that has erupted within the past few centuries and will likely erupt again

active volcano

Tiny solid particles or liquid droplets that remain suspended in the atmosphere for a long time.

aerosol

A gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions.

alluvial fan

The process of magma contamination in which blocks of wall rock fall into a magma chamber and dissolve.

assimilation

A clastic sedimentary rock containing both quartz and feldspar grains.

arkose

A vast composite, intrusive, igneous rock body up to several hundred km long and 100 km wide, formed by the intrusion of numerous plutons in the same region.

batholith

A distinct layer of sediment or sedimentary rock, typically reflecting continuous deposition during a relatively short time interval.

bed

Sedimentary rock formed from material (such as shells) produced by living organisms

biochemical sedimentary rock

Large, angular pyroclastic fragments consisting of volcanic rock, broken up during the eruption.

block

Lava that is so viscous that it breaks into boulder-like blocks as it moves; typically, such lavas are andesitic or rhyolitic.

blocky lava

Larger blobs of lava that squirt out of a vent and then solidify become streamlined bombs, whose surfaces are typically streaked and polished.

bomb

Coarse sedimentary rock consisting of angular fragments; or rock broken into angular fragments by faulting.

breccia

A large circular depression with steep walls and a fairly flat floor, formed after an eruption as the center of the volcano collapses into the drained magma chamber below

caldera

The phase of lithification in which cement, consisting of minerals that precipitate from groundwater, partially or completely fills the spaces between clasts and attaches each grain to its neighbor.

cementation

Sedimentary rocks made up of minerals that precipitate directly from water solution.

chemical sedimentary rock

A subaerial volcano consisting of a cone-shaped pile of tephra whose slope approaches the angle of repose for tephra.

cinder cone

Sedimentary rock consisting of cemented-together detritus derived from the weathering of preexisting rock.

clastic sedimentary rock

A black, organic rock consisting of greater than 50% carbon; it forms from the buried and altered remains of plant material.

coal

A type of fracturing that yields roughly hexagonal columns of basalt; columnar joints form when a dike, sill, or lava flow cools.

columnar jointing

The phase of lithification in which the pressure of the overburden on the buried rock squeezes out water and air that was trapped between clasts, and the clasts press tightly together.

compaction

Very coarse-grained sedimentary rock consisting of rounded clasts

conglomerate

Thick salt deposits that form as a consequence of precipitation from saline water.

evaporite

Violent volcanic eruptions that produce clouds and avalanches of pyroclastic debris

explosive eruption

A volcano that was active in the past but has now shut off entirely and will not erupt in the future.

extinct volcano

Rock that forms by the freezing of lava above ground, after it flows or explodes out (extrudes) onto the surface and comes into contact with the atmosphere or ocean.

extrusive igneous rock

A conduit in a magma chamber in the shape of a long crack through which magma rises and erupts at the surface.

fissure

Vast sheets of basalt that spread from a volcanic vent over an extensive surface of land; they may form where a rift develops above a continental hot spot, and where lava is particularly hot and has low viscosity.

flood basalt

The empty space left when a lava tunnel drains; this happens when the surface of a lava flow solidifies while the inner part of the flow continues to stream downslope.

lava tube

The transformation of loose sediment into solid rock through compaction and cementation.

lithification

The melting in a rock of the minerals with the lowest melting temperatures, while other minerals remain solid.

partial melting

The rind of a pillow momentarily stops the flow's advance, but within minutes the pressure of the lava squeezing into the pillow breaks the rind, and a new blob of lava squirts out, freezes, and produces another pillow. A flow made of these blobs is called pillow lava.

pillow lava

An irregular or blob-shaped intrusion; can range in size from tens of m across to tens of km across

pluton

A glassy igneous rock that forms from felsic frothy lava and contains abundant (over 50%) pore space.

pumice

Fragmented material that sprayed out of a volcano and landed on the ground or sea floor in solid form.

pyroclastic debris

A fast-moving avalanche that occurs when hot volcanic ash and debris mix with air and flow down the side of a volcano.

pyroclastic flow

Rock made from fragments that were blown out of a volcano during an explosion and were then packed or welded together.

pyroclastic rock

The seaward migration of a shoreline caused by a lowering of sea level.

regression

Relatively small elongated ridges that form on a sedimentary bed surface at right angles to the direction of current flow.

ripple mark

Coarse-grained sedimentary rock consisting almost entirely of quartz.

sandstone

A glassy, mafic, igneous rock containing abundant air-filled holes.

scoria

A depression, created as a consequence of subsidence, that fills with sediment.

sedimentary basin

A relict of wall rock surrounded by intrusive rock when the intrusive rock freezes.

xenolith

A lava flow with a rubbly surface.

a'a'

(1) A circular depression at the top of a volcanic mound; (2) a depression formed by the impact of a meteorite.

crater

Internal laminations in a bed, inclined at an angle to the main bedding; cross beds are a relict of the slip face of dunes or ripples.

cross bed

A rock that consists of minerals that grew when a melt solidified, and eventually interlock like pieces of a jigsaw puzzle.

crystalline igneous rock

A wedge of sediment formed at a river mouth when the running water of the stream enters standing water, the current slows, the stream loses competence, and sediment settles out.

delta

The process by which sediment settles out of a transporting medium.

deposition

A setting in which sediments accumulate; its character (fluvial, deltaic, reef, glacial, etc.) reflects local conditions.

depositional environment

All of the physical, chemical, and biological processes that transform sediment into sedimentary rock and that alter the rock after the rock has formed.

diagenesis

A tabular (wall-shaped) intrusion of rock that cuts across the layering of country rock.

dike

A name sometimes used for a carbonate rock containing a high proportion of dolomite.

dolostone

A volcano that has not erupted for hundreds to thousands of years but does have the potential to erupt again in the future.

dormant volcano

A pile of sand generally formed by deposition from the wind.

dune

An eruption that yields mostly lava, not ash.

effusive eruption

The grinding away and removal of Earth's surface materials by moving water, air, or ice.

erosion

Episodes when volcanoes extrude lava and pyroclastic debris.

eruption

The character of a particular volcanic eruption; geologists name styles based on typical examples (e.g., Hawaiian, Strombolian).

eruptive style

The remnant, or trace, of an ancient living organism that has been preserved in rock or sediment.

fossil

The process by which a magma becomes progressively more silicic as it cools, because early-formed crystals settle out.

fractional crystallization

A rock consisting of igneous chunks and/or shards that are packed together, welded together, or cemented together after having solidified.

fragmental igneous rock

Igneous rock consisting entirely of glass, or of tiny crystals surrounded by a glass matrix

glassy igneous rock

A layer of sediment, deposited by a turbidity current, in which grain size varies from coarse at the bottom to fine at the top.

graded bed

Rock that forms when hot molten rock (magma or lava) cools and freezes solid.

igneous rock

Any pyroclastic particle that is 2 to 64 mm in diameter (i.e., marble-sized); the particles can consist of frozen lava clots, pumice fragments, or ash clumps.

lapilli

A region in which huge volumes of lava and/or ash erupted over a relatively short interval of geologic time.

large igneous province (LIP)

Molten rock that has flowed out onto the Earth's surface.

lava

A dome-like mass of rhyolitic lava that accumulates above the eruption vent.

lava dome

Sheets or mounds of lava that flow onto the ground surface or sea floor in molten form and then solidify.

lava flow

A column of molten lava spraying upward under pressure from a volcanic vent.

lava fountains

Molten rock beneath the Earth's surface

magma

A space below ground filled with magma.

magma chamber

Very fine-grained sedimentary rock that will not easily split into sheets.

mudstone

An igneous rock consisting of a solid mass of volcanic glass.

obsidian

Shale containing kerogen.

oil shale

Sedimentary rock (such as coal) formed from carbon-rich relicts of organisms

organic sedimentary rock

A lava flow with a surface texture of smooth, glassy, ropelike ridges.

pahoehoe

Rock that forms either by the cementing together of fragments broken off preexisting rock or by the precipitation of mineral crystals out of water solutions at or near the Earth's surface.

sedimentary rock

A distinctive shape or form (examples—bed, ripple mark, cross bed) formed during deposition of sediment.

sedimentary structure

Very fine-grained sedimentary rock that breaks into thin sheets.

shale

A subaerial volcano with a broad, gentle dome, formed either from low-viscosity basaltic lava or from large pyroclastic sheets.

shield volcano

A nearly horizontal tabletop-shaped tabular intrusion that occurs between the layers of country rock.

sill

Fine-grained sedimentary rock generally composed of very small quartz grains.

siltstone

Rhyolitic lava freezes while still in the vent and then pushes upward as a column-like spire up to 100 m above the vent.

spire

A large, cone-shaped subaerial volcano consisting of alternating layers of lava and tephra

stratovolcano

A volcano that erupts a vast amount (more than 1,000 cubic km) of volcanic material during a single event; none have erupted during recorded human history.

supervolcano

A basaltic volcanic glass

tachylite

Unconsolidated accumulations of pyroclastic grains.

tephra

A pyroclastic igneous rock composed of volcanic ash and fragmented pumice, formed when accumulations of the debris cement together.

tuff

Open holes in igneous rock formed by the preservation of bubbles in magma as the magma cools into solid rock.

vesicle

The resistance of material to flow.

viscosity

A curving chain of active volcanoes formed adjacent to a convergent plate boundary.

volcanic arc

Tiny glass shards formed when a fine spray of exploded lava freezes instantly upon contact with the atmosphere.

volcanic ash

A mixture of water and pyroclastic debris that moves downslope like wet concrete.

volcanic debris flow

(1) A vent from which melt from inside the Earth spews out onto the planet's surface; (2) a mountain formed by the accumulation of extrusive volcanic rock.

volcano