DSST Introduction to Geology flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Mohorovičić discontinuity

The boundary between Earth's crust and mantle, marked by a sharp increase in seismic wave velocity; its depth is about 5-10 km under oceans and 30-70 km under continents.

Asthenosphere

The plastic, partially molten layer of the upper mantle beneath the rigid lithosphere; it allows plate motion by flowing slowly over geologic time and is a source of basaltic magma.

Bowen's reaction series

The sequence in which minerals crystallize from cooling magma: olivine and Ca-plagioclase first, then pyroxene, amphibole, biotite, and finally quartz and K-feldspar at the lowest temperatures.

Phaneritic texture

An igneous rock texture with visible, coarse-grained crystals, indicating slow cooling at depth (intrusive). Examples include granite and gabbro.

Foliation

Parallel alignment of platy or elongated minerals in metamorphic rock, formed perpendicular to maximum compressive stress. Examples: slate, schist, gneiss.

Angular unconformity

An unconformity where tilted or folded sedimentary layers are truncated by erosion and then overlain by younger, roughly horizontal layers, indicating a period of deformation followed by erosion.

Half-life

The time required for half of a radioactive parent isotope to decay to daughter products. After n half-lives, the remaining parent fraction is (1/2)^n.

Mohs hardness scale

A relative scale from 1 (talc) to 10 (diamond) ranking minerals by scratch resistance. A mineral scratches those with lower numbers and is scratched by higher ones.

Hydrolysis weathering

A chemical weathering process in which water reacts with minerals, especially feldspar, to form clay minerals. It is favored by warm, wet climates.

Soil horizons

Layers of a soil profile: O (organic), A (topsoil), E (leached), B (accumulation), C (weathered parent material), and R (bedrock).

Stream competence

The largest particle size a stream can transport, determined by flow velocity. Competence increases sharply with velocity; capacity is the total sediment load.

Base level

The lowest elevation to which a stream can erode. Sea level is the ultimate base level; lakes and resistant rock layers act as temporary local base levels.

Dendritic drainage

A branching, tree-like drainage pattern that develops on relatively uniform rock or sediment, with tributaries joining larger streams at acute angles.

Water table

The upper surface of the saturated zone in groundwater, below which all pores are filled with water; it rises and falls with recharge and discharge.

Darcy's law

Groundwater discharge Q equals hydraulic conductivity K times hydraulic gradient i times cross-sectional area A (Q = K i A). It describes flow through porous media.

Cirque

A bowl-shaped depression carved by glacial erosion at the head of an alpine valley. Adjacent cirques can form arêtes and horns.

Drumlin

A streamlined, teardrop-shaped hill of glacial till, with the blunt end pointing up-ice and the tapered end pointing down-ice, recording the direction of glacier flow.

Longshore drift

The movement of sediment along a coastline by waves approaching at an angle, producing spits, tombolos, and barrier islands.

Divergent boundary

A plate boundary where plates move apart, producing mid-ocean ridges or continental rifts, normal faulting, shallow earthquakes, and basaltic volcanism.

Subduction zone

A convergent boundary where one plate descends beneath another, producing a trench, deep earthquakes, accretionary wedges, and volcanic arcs.

Magnetic striping

Symmetrical bands of alternating magnetic polarity on the seafloor, recording reversals of Earth's field as new crust formed at a spreading ridge; key evidence for seafloor spreading.

Hot spot

A fixed mantle plume that produces volcanic chains as a plate moves over it, such as the Hawaiian Islands and Yellowstone.

Anticline

A fold in which layers arch upward, with the oldest rocks in the core. It commonly forms structural traps for oil and gas.

Normal fault

A fault where the hanging wall moves down relative to the footwall, caused by tensional stress and typical of rifts and divergent boundaries.

P-wave

A compressional seismic wave that is the fastest body wave and can travel through solids and liquids. It arrives first at a seismograph.

Epicenter

The point on Earth's surface directly above the earthquake focus (hypocenter). It is located using P- and S-wave arrival-time differences at three or more stations.

Stratovolcano

A steep, symmetrical volcano built of alternating lava and pyroclastic layers, typically andesitic and explosive. Examples include Fuji and Vesuvius.

Coal rank

The progressive increase in coal maturity with heat and pressure: peat, lignite, bituminous, anthracite. Higher rank means higher carbon content and energy density.

Petroleum trap

A geologic configuration (anticline, fault, or salt dome) where oil and gas accumulate because impermeable cap rock prevents further migration.

Liquefaction

Loss of strength in saturated, loose sandy sediment during earthquake shaking, causing it to behave like a fluid and damage foundations and buried utilities.

Lahar

A volcanic mudflow or debris flow formed when water mixes with volcanic ash and debris, often triggered by eruptions melting snow or heavy rain; highly destructive.

Karst topography

Landscape formed by dissolution of limestone, featuring caves, sinkholes, disappearing streams, and irregular terrain; groundwater flow is concentrated in conduits.