Geology Mid Term

aa

A type of lava flow characterized by a rough, jagged, and blocky surface.

Aphanitic

An igneous rock texture characterized by fine-grained crystals, indicating rapid cooling at or near Earth's surface (extrusive).

Asthenosphere

The weak, ductile layer of the upper mantle below the lithosphere, where convection currents drive plate tectonics.

Atom

The basic unit of a chemical element, consisting of a nucleus (protons and neutrons) and orbiting electrons.

Basalt

A common fine-grained, mafic igneous rock, typically forming oceanic crust.

Body Wave

Seismic waves that travel through the Earth's interior, including P-waves and S-waves.

Caldera

A large, basin-shaped depression formed when the roof of a magma chamber collapses after an eruption.

Calcite

A common mineral, calcium carbonate (CaCO3), which is the primary component of limestone and marble and effervesces in acid.

Chemical Sedimentary Rocks

Rocks formed from the precipitation of minerals from water or from biological processes (e.g., limestone, rock salt).

Clastic Sedimentary Rocks

Rocks formed from fragments (clasts) of pre-existing rocks, which are transported, deposited, and lithified (e.g., sandstone).

Cleavage

The tendency of a mineral to break along smooth, flat planes of weakness in its crystal structure.

Composite Volcano (Stratovolcano)

A tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and ash, typically associated with felsic magma and explosive eruptions.

Continental Drift

Alfred Wegener's hypothesis that the continents have moved over geologic time relative to each other, largely superseded by plate tectonics.

Convergent Plate Boundary

A plate boundary where two plates move toward each other, resulting in subduction or continental collision.

Core

The innermost layer of Earth, composed primarily of iron and nickel, with a liquid outer core and a solid inner core.

Covalent Bond

A chemical bond formed by the sharing of electrons between atoms.

Crust

The outermost solid layer of Earth, divided into thinner, denser oceanic crust and thicker, less dense continental crust.

Crystal

A solid material whose atoms, molecules, or ions are arranged in an ordered pattern extending in all three spatial dimensions.

Divergent Plate Boundary

A plate boundary where two plates move away from each other, resulting in the creation of new crust (e.g., mid-ocean ridges).

Elastic Rebound Theory

The theory explaining how earthquakes are generated

Element

A pure substance consisting of only one type of atom, which cannot be broken down into simpler substances by ordinary chemical means.

Epicenter

The point on Earth's surface directly above the focus (origin) of an earthquake.

Erosion

The process of transporting weathered rock and soil materials by agents such as water, wind, ice, and gravity.

Extrusive (Volcanic) Rock

Igneous rocks that form from lava cooling rapidly at or near Earth's surface, resulting in fine-grained (aphanitic) or glassy textures.

Fault

A fracture or zone of fractures in the Earth's crust where there has been observable displacement.

Felsic

Igneous rocks or magma rich in silica, potassium, and sodium, generally light in color and high in viscosity.

Feldspar

A group of abundant rock-forming tectosilicate minerals that make up about 60% of the Earth's crust. Chemical weathering of feldspars produces clay minerals.

Ferromagnesium

Minerals (typically silicates) containing iron and magnesium, making them generally dark in color and denser.

Focus

The point within the Earth where an earthquake rupture initiates.

Foliation

A planar arrangement of mineral grains or structural features within a rock, typically resulting from directed pressure during metamorphism.

Gabbro

A coarse-grained, mafic igneous rock, equivalent to basalt but cooled slowly below the surface (intrusive).

Granite

A coarse-grained, felsic igneous rock, typically forming continental crust and cooled slowly below the surface (intrusive).

Hardness

A mineral's resistance to scratching, measured by Mohs Hardness Scale.

Hot Spot

An area of volcanic activity that is independent of plate boundaries, caused by plumes of hot mantle material rising to the surface.

Igneous Rock

Rocks formed from the cooling and solidification of molten magma or lava.

Ion

An atom or molecule that has gained or lost one or more electrons, resulting in a net electrical charge.

Ionic Bond

A chemical bond formed by the electrostatic attraction between oppositely charged ions.

Intrusive (Plutonic) Rock

Igneous rocks that form from magma cooling slowly beneath Earth's surface, resulting in coarse-grained (phaneritic) textures.

Isotope

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Lahar

A destructive mudflow on the slopes of a volcano, consisting of pyroclastic material and water.

Limestone

A chemical or biogenic sedimentary rock composed primarily of calcium carbonate (calcite).

Liquefaction

A process by which saturated granular soils temporarily lose strength and behave as a liquid during an earthquake.

Lithification

The process by which loose sediment is transformed into solid rock, involving compaction and cementation.

Lithosphere

The rigid outermost layer of Earth, consisting of the crust and the uppermost part of the mantle; broken into tectonic plates.

Luster

The way light reflects off the surface of a mineral (e.g., metallic, glassy, dull).

Mafic

Igneous rocks or magma rich in magnesium and iron, generally dark in color and low in viscosity.

Magma

Molten rock material beneath Earth's surface.

Magnetic Reversal

A change in Earth's magnetic field where the north and south magnetic poles switch places. Recorded in magnetic stripes on the seafloor.

Magnetic Stripes

Alternating bands of rock on the seafloor with normal and reversed magnetic polarity, providing evidence for seafloor spreading.

Magnitude

A measure of the energy released during an earthquake. The Moment Magnitude Scale (Mw) is preferred by seismologists.

Mantle

The layer of Earth between the crust and the core, composed of dense, hot, solid rock that flows slowly over geologic time.

Marble

A non-foliated metamorphic rock formed from the metamorphism of limestone, composed of recrystallized calcite.

Mesosphere

The lower part of the mantle, below the asthenosphere, which is more rigid due to increased pressure.

Metamorphic Rock

Rocks formed from pre-existing rocks that have been transformed by heat, pressure, or chemical alteration.

Mineral

A naturally occurring, inorganic, crystalline solid with a definite chemical composition.

Modified Mercalli Scale

An earthquake intensity scale that measures the observed effects of an earthquake on people, buildings, and infrastructure.

Moho (Mohorovičić discontinuity)

The boundary between the Earth's crust and the mantle.

Normal Fault

A type of fault where the hanging wall moves down relative to the footwall, caused by extensional stress.

Oceanic Crust

The thinner, denser part of Earth's crust, primarily composed of basalt and gabbro.

P-wave (Primary Wave)

A type of body wave that is a compressional wave, traveling fastest and capable of passing through solids, liquids, and gases.

Pahoehoe

A type of lava flow characterized by a smooth, ropy, or billowy surface.

Pangaea

The supercontinent proposed by Alfred Wegener, which existed during the late Paleozoic and early Mesozoic eras.

Phaneritic

An igneous rock texture characterized by coarse-grained crystals, indicating slow cooling below Earth's surface (intrusive).

Plate (Lithospheric/Tectonic)

Large, rigid slab of lithosphere that moves over the asthenosphere.

Plate Tectonics

The theory that Earth's outer shell is divided into several large plates that move over the mantle, causing earthquakes, volcanoes, and mountain building.

Pyroclastic Flow

A fast-moving current of hot gas and volcanic debris (ash, pumice, rock fragments) that flows down the side of a volcano.

Quartz

A common mineral, silicon dioxide (SiO2), which is hard, resistant to weathering, and found in many igneous, sedimentary, and metamorphic rocks.

Quartzite

A non-foliated metamorphic rock formed from the metamorphism of quartz-rich sandstone.

Recurrence Interval

The average time between successive geological events, such as earthquakes or floods, of a specific magnitude in a particular area.

Reverse Fault

A type of fault where the hanging wall moves up relative to the footwall, caused by compressional stress.

Richter Magnitude Scale

An older, logarithmic scale used to measure earthquake magnitude based on the amplitude of seismic waves. Largely superseded by Moment Magnitude.

Ridge (Mid-ocean)

An underwater mountain range formed at a divergent plate boundary where new oceanic crust is created.

Rift

A linear zone where Earth's crust and lithosphere are being pulled apart.

Rock

A solid aggregate of one or more minerals, glass, or solidified organic matter.

S-wave (Secondary Wave)

A type of body wave that is a shear wave, traveling slower than P-waves and only capable of passing through solids.

Seafloor Spreading

The process by which new oceanic crust is formed at mid-ocean ridges and moves away from the ridge.

Sedimentary Rocks

Rocks formed from the accumulation and lithification of sediments (weathered rock fragments, organic matter, or chemical precipitates).

Seismic Gap

A segment of an active fault that has not experienced an earthquake for a relatively long period, and thus is considered to have a high potential for a future earthquake.

Seismograph

An instrument used to detect and record seismic waves.

Shield Volcano

A broad, gently sloping volcano built by the effusive eruption of fluid, mafic lava.

Silicate Minerals

The most common group of minerals, characterized by the silicon-oxygen tetrahedron (SiO4) as their fundamental building block.

Strain

The deformation or change in shape and size of a rock body as a result of stress.

Stress

The force per unit area acting on a rock.

Strike-slip Fault

A type of fault where the blocks on either side move horizontally past each other, caused by shearing stress.

Subduction

The process where one tectonic plate is forced beneath another plate at a convergent boundary.

Subduction Zone

An area where oceanic crust is being subducted beneath another plate.

Thrust Fault

A low-angle reverse fault, where the hanging wall moves up and over the footwall.

Transform Plate Boundary

A plate boundary where two plates slide horizontally past each other.

Trench (Oceanic)

A long, narrow, deep depression in the ocean floor, typically formed at a convergent plate boundary where oceanic crust is subducted.

Viscosity

A measure of a fluid's resistance to flow; higher viscosity magma is more resistant to flow and tends to produce more explosive eruptions.

Volcanic Arc

A chain of volcanoes formed above a subducting plate, typically found on the overriding plate in a subduction zone.

Weathering

The set of physical and chemical processes that break down rocks and minerals at or near Earth's surface.