Earth Science: Deformation, Metamorphism, Geologic Time, Earthquakes, and Water Systems

Vocabulary flashcards covering geologic deformation, faults, folds, metamorphic processes, geologic dating, earthquake dynamics, glacial landforms, slope stability, and hydrogeology.

Stress Field

The entire array of stresses from all directions affecting any point within the Earth.

Confining Pressure

A condition where a rock experiences the same amount of force (stress) from each direction.

Differential Stress

Stress that occurs when tectonics or other sources change pressure to be greater in some directions than in others.

Compression

Differential stress where pressure pushes towards the rock, causing it to deform, fracture, or fold.

Tension

Differential stress where pressure pulls outward away from the rock, causing it to stretch, fracture, or form veins.

Shear

Differential stress where pressure pulls the edges of the rock in opposite directions.

Dip

The steepness of the fault surface.

Strike

The direction of a horizontal line on an included surface.

Hanging Wall

The block of rock located above the fault.

Footwall

The block of rock located below the fault.

Normal Fault

A fault where the hanging wall moves down relative to the footwall, typically caused by tension.

Reverse Fault

A fault where the hanging wall moves up relative to the footwall, typically caused by horizontal compression.

Strike-Slip Fault

A fault where rocks move with a side-to-side motion parallel to the strike of the fault surface.

Anticline

A fold shaped like an $'A'$.

Syncline

A fold shaped like a $'U'$.

Monocline

A fold that dips down in one direction and then flattens out.

Cleavage

A cut in the rock metamorphic fabric.

Foliation

Any planar metamorphic fabric, such as Schist, metamorphosed conglomerate, or Gneiss.

Contact Metamorphism

Metamorphism caused by local heating by magma, typically occurring without deformation.

Regional Metamorphism

Metamorphism involving deformation and heating over a broad region, often due to burial and tectonic stresses.

Relative Dating

Determining the age of a rock relative to another through layering, fractures, or dikes.

Isotopic Dating

Chemically analyzing a rock for products of natural radioactive decay to determine the parent to daughter ratio.

Principle of Superposition

The rule that older rock layers are found on the bottom and newer layers are on the top.

Angular Unconformity

A sequence where rock beds are folded and eroded before new sediment like conglomerate is deposited on top.

Nonconformity

A sequence where a nonlayered rock formed at depth is uplifted and eroded before being buried by new sediment.

Disconformity

An unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition.

Ice Cores

Samples of ice that provide evidence of Earth's history by showing environments captured in ice.

Varves

Sedimentary layers that show the environment and seasons over time.

Hypocenter

The exact location within the Earth where an earthquake is generated.

Epicenter

The location on the Earth's surface directly above the hypocenter.

Elastic Behavior

A response where rocks return to their original shape after being strained once stress is reduced by faulting.

P-waves

The fastest seismic waves; they compress rock in the same direction as propagation and travel through both solids and liquids.

S-waves

Seismic waves that shear the rock side to side or up and down; they travel only through solids.

Rayleigh Waves

Surface waves that move up and down in an elliptical path and cause the most damage.

Love Waves

Surface waves that shuffle side to side, often sliding buildings off their foundations.

Seismograph

An instrument consisting of three seismometers oriented $90$ degrees from each other to record motion from any direction.

Earthquake Magnitude

A logarithmic scale where a one-unit increase represents a tenfold increase in ground motion.

Modified Mercalli Intensity Rating (MMI)

A rating where $1$ is the farthest from the earthquake; higher numbers indicate closer proximity and increased damage.

Liquefaction

A process during an earthquake where soil loses its strength and behaves like a liquid, causing buildings to collapse.

Ice Sheets

Regionally continuous masses of ice covering large areas like Antarctica and Greenland.

Alpine Glaciers

Fairly narrow glaciers that flow down valleys for tens of kilometers.

Abrasion

Glacial erosion where rock and sediment at the base scrape at the underlying bedrock, creating striations.

Plucking

Glacial erosion where rocks below the glacier are grabbed by the ice and moved from their origin.

Till

Unsorted and unstratified clasts deposited directly from a glacier.

Moraines

Accumulations of debris deposited by glaciers; types include lateral, medial, terminal, ground, and recessional.

Cirques

Bowl-shaped depressions formed by glacial erosion.

Tarns

Lakes located within cirques.

Aretes

Sharp ridges that have been glacially eroded from both sides.

Horns

Pyramid-like peaks formed where three or more cirques merge by headward erosion.

Eskers

Long, sinuous ridges formed by sediment deposited in meltwater channels as a glacier melts back.

Kames

Sediment deposits formed in ice crevasses or between the glacier and the land surface by meltwater.

Kettles

Pits or holes created when abandoned ice blocks melt within outwash sediment.

Drumlins

Tear-drop shaped landforms created as a moving glacier sculpts soft materials.

Angle of Repose

The steepest angle at which loose material remains stable on a slope.

Creep

A slow type of slope failure where the ground surface bends downhill.

Drainage Basin

The naturally defined area drained by a stream.

Drainage Divide

The ridge or boundary between two drainage basins.

Dendritic Drainage Pattern

A treelike drainage pattern occurring where rocks have uniform resistance to erosion.

Braided Streams

A network of interweaving, sinuous channels that is overall relatively straight.

Meandering Streams

High-sinuosity streams that are very curved.

Point Bar

Sediment deposited on the inside bend of a meandering stream where velocity is lower.

Cutbank

The deeper, outside part of a stream bend characterized by erosion.

Oxbow Lakes

C-shaped depressions containing water that have been abandoned by a stream.

Water Table

The top of the saturated zone that typically follows the topography.

Porosity

The measure of how much water a material can hold based on its pore space.

Permeability

The ability of a rock or sediment to transmit or flow water.

Unconfined Aquifer

An aquifer where water can seep directly from the surface through the unsaturated zone.

Confined Aquifer

An aquifer separated from the surface by rocks with low permeability, preventing direct seepage.