GEOS 1303: Volcanism, Earthquakes, and Mountain Building Review

Comprehensive vocabulary flashcards covering the mechanisms of volcanic eruptions, earthquake seismology, seismic wave behavior, plate boundary dynamics, and mountain building.

Cinder cone

A small, steep-sided volcano constructed from loose fragments of pyroclastic debris ejected from a single central vent.

Decompression melting

The melting of mantle rock beneath mid-ocean ridges and continental rifts that occurs when confining pressure drops as rock rises upward.

Flux melting

The process at subduction zones where water released from a descending tectonic slab lowers the melting temperature of the overlying mantle wedge.

Lahar

A fast-moving volcanic mudflow composed of pyroclastic debris and ash mixed with water that channels rapidly down river valleys.

Effusive eruption

A volcanic eruption characterized by low-viscosity, runny lava pouring out steadily onto the surface rather than fragmenting explosively.

Viscosity

A fluid's internal resistance to flow; silica-rich magma has high viscosity, which traps volatile gases and drives explosive eruptions.

Stratovolcano (Composite volcano)

A steep, conical volcano composed of alternating layers of pyroclastic debris and viscous intermediate-to-felsic lavas (such as andesite and rhyolite) prone to explosive eruptions.

Shield volcano

A broad, gently sloping volcano built by successive flows of low-silica, low-viscosity basaltic lava that erupts effusively.

Volcanic arc

A curved chain of volcanoes that develops along a convergent plate boundary above a subducting oceanic plate, forming either an island arc or a continental arc.

Hot spot

An isolated center of volcanic activity caused by a rising mantle plume independent of plate boundaries, producing age-progressive volcanic chains as a plate moves over it.

Transform boundary volcanism

A tectonic setting where volcanism is absent because plates slide horizontally past one another without rising mantle decompression or water addition.

Pyroclastic debris

Fragmented solid volcanic material, including ash, lapilli, pumice, and blocks, violently ejected during an explosive eruption.

Focus (Hypocenter)

The underground origin point along a fault plane where seismic energy is first released during an earthquake.

Epicenter

The geographic location on Earth's surface located directly above the focus of an earthquake.

Wadati-Benioff zone

A planar, inclined band of earthquake foci tracing the subducting oceanic slab dipping beneath an overriding plate from shallow to deep depths.

Asthenosphere

The weak, ductile upper mantle layer situated immediately below the lithosphere, corresponding to a low-velocity zone where seismic waves slow down due to partial melting.

P-wave

A primary compressional body wave that travels fastest through rock, displacing particles parallel to wave propagation, and can pass through solids, liquids, and gases.

S-wave

A secondary shear body wave that vibrates rock perpendicular to propagation and cannot transmit through liquids, causing it to stop at Earth's outer core.

Epicenter triangulation

The geometric procedure requiring data from at least $3$ seismograph stations to locate an epicenter by plotting intersecting distance circles derived from $S-P$ time delays.

Elastic rebound theory

The model describing how friction locks a fault (stick) while tectonic motion accumulates elastic strain until frictional resistance is overcome, causing slip and releasing energy as seismic waves.

Moho (Crust–mantle boundary)

The seismic boundary separating Earth's crust from the mantle, marked by a sharp jump in seismic wave velocity and wave refraction due to increased density.

Mantle–outer core boundary

The internal boundary where S-waves stop completely due to liquid outer core conditions and P-waves experience deceleration and significant refraction.

Liquefaction

The seismic hazard where earthquake shaking causes water-saturated, unconsolidated sediment to lose shear strength and behave temporarily like a viscous fluid.

Orogenesis

The complete geological process of mountain building involving both crustal deformation and tectonic uplift.

Stress

The magnitude of tectonic force applied per unit area of rock, expressed as tension, compression, or shear.

Strain

The measurable change in size, volume, or shape of a rock mass that results from an applied stress.

Tension

A directional stress that pulls crustal rocks apart and stretches them horizontally, producing normal faults.

Normal fault

A dip-slip fault formed under tensional stress where the hanging wall block displaces downward relative to the footwall block.

Reverse fault

A dip-slip fault formed under compressional stress where the hanging wall block displaces upward relative to the footwall block.

Anticline

An upward-arching fold in rock strata produced by ductile compressive deformation.

Syncline

A downward-curving, trough-shaped fold in rock strata produced by ductile compressive deformation.

Crustal thickening

The vertical expansion and horizontal shortening of continental crust during tectonic collisions, generating high topography and a deep buoyant crustal root.