Earth and Space Terms

Sediment

Loose particles of rock, minerals, or organic material.

Clastic

Sedimentary rocks made from fragments of other rocks.

Detrital Sedimentary Rock

Another name for clastic sedimentary rock.

Biochemical

Sedimentary rocks formed from the remains of living things.

Chemical Sedimentary Rock

Rocks formed from minerals precipitated from water.

Nonclastic

Sedimentary rocks not formed from fragments of other rocks (includes biochemical and chemical types).

Compaction

The process where sediment is squeezed together by the weight of overlying material.

Cementation

The process where minerals precipitate in the spaces between sediment grains, gluing them together.

Lithification

The process of turning sediment into rock, including compaction and cementation.

Beds (Strata)

Layers of sedimentary rock.

Bedding Plane

The boundary between two layers of sedimentary rock.

Cross-bedding

Layers within a bed that are inclined to the main bedding planes, indicating current direction.

Graded Bed

A bed where the grain size changes from coarse at the bottom to fine at the top.

Mud Crack

Cracks that form in mud as it dries.

Ripple Mark

Wavy features formed on the surface of sediment by wind or water currents.

Salt Flat

A flat area covered with salt deposits, formed by the evaporation of water.

Evaporate Deposit

A sedimentary rock formed from minerals that precipitate as water evaporates.

Facies

A body of rock with specific characteristics that reflect the environment in which it was formed.

Fissility

The tendency of a rock to split along closely spaced planes.

Fossil

Preserved remains or traces of organisms.

Sorting

The process by which sediment grains are separated by size or density.

Metamorphism

The process by which rocks are changed by heat, pressure, or chemical reactions.

Aureole

A zone of altered rock around an igneous intrusion.

Contact Metamorphism

Metamorphism that occurs when rock is heated by contact with magma.

Regional Metamorphism

Metamorphism that occurs over a large area, usually due to tectonic forces.

Foliation

The layering or banding in metamorphic rocks caused by the alignment of minerals.

Nonfoliated

Metamorphic rocks that do not have a layered or banded appearance.

Rock Cleavage

The tendency of a rock to break along specific planes.

Slaty Cleavage

A type of rock cleavage that causes rocks to break into thin, flat slabs.

Schistosity

A type of foliation in which platy minerals are aligned to form a layered structure.

Gneiss

A metamorphic rock with a banded appearance.

Migmatite

A rock that is part igneous and part metamorphic.

Hydrothermal Solution

Hot, chemically active fluids within the Earth.

Index Mineral

A mineral that is characteristic of a particular metamorphic grade.

Shear

A type of stress that causes rocks to slide past each other.

Stress

Force acting on a rock.

Stream

A channel that carries flowing water.

Alluvial Fan

A fan-shaped deposit of sediment formed where a stream flows out of a mountain canyon.

Alluvium

Sediment deposited by a stream.

Antecedent Stream

A stream that maintains its course even as the land around it is uplifted.

Back Swamp

A low-lying area on a floodplain that is poorly drained.

Bar

A deposit of sediment in a stream channel.

Base Level

The lowest point to which a stream can erode.

Bed Load

Sediment that is transported along the bottom of a stream.

Braided Stream

A stream with multiple channels that intertwine.

Capacity

The maximum amount of sediment that a stream can carry.

Competence

The largest size of sediment that a stream can carry.

Cut Bank

The eroded bank on the outside of a meander.

Cutoff

A shortcut formed when a meander is cut off.

Delta

A deposit of sediment formed where a river enters a lake or ocean.

Dendritic Pattern

A branching stream pattern.

Discharge

The volume of water that flows past a point in a stream in a given time.

Dissolved Load

Material that is dissolved in stream water.

Distributary

A small stream that branches out from a larger stream in a delta.

Divide

The boundary between two drainage basins.

Drainage Basin

The area of land drained by a stream and its tributaries.

Entrenched Meander

A meander that is cut deep into the ground.

Evapotranspiration

The combined loss of water from a surface by evaporation and transpiration.

Floodplain

A flat area adjacent to a stream that is subject to flooding.

Graded Stream

A stream in which the slope and channel characteristics are adjusted so that the stream can transport its load efficiently.

Gradient

The slope of a stream channel.

Head (Headwaters)

The source of a stream.

Headward Erosion

Erosion that occurs at the head of a stream.

Hydrologic Cycle

The continuous movement of water between the oceans, atmosphere, and land.

Infiltration

The process by which water soaks into the ground.

Infiltration Capacity

The maximum rate at which water can infiltrate the ground.

Lag Time

The time between the peak of rainfall and the peak of streamflow.

Laminar Flow

Smooth, layered flow of water.

Local (Temporary) Base Level

A temporary base level, such as a lake or reservoir.

Longitudinal Profile

A graph of the elevation of a stream channel along its length.

Meander

A bend in a stream.

Meander Scar

A mark left on the landscape by a former meander.

Mouth

The point where a stream flows into a larger body of water.

Natural Levee

A raised bank along a stream channel, formed by the deposition of sediment during floods.

Oxbow Lake

A lake formed when a meander is cut off.

Peneplain

A nearly flat, featureless landscape formed by erosion.

Playfair's Law

The law that states that valleys will erode to form a graded profile.

Point Bar

A deposit of sediment on the inside of a meander.

Pothole

A hole eroded in the bedrock by the swirling action of water and sediment.

Radial Pattern

A stream pattern in which streams flow outward from a central point.

Rapids

A section of a stream with fast-moving, turbulent water.

Rectangular Pattern

A stream pattern with many right angles.

Rejuvenated Stream

A stream that has had its base level lowered, causing it to erode more actively.

Runoff

Water that flows over the surface of the ground.

Saltation

The movement of sediment by a series of short jumps.

Settling Velocity

The speed at which a particle falls through a fluid.

Sheetflow

Unconcentrated flow of water over a surface.

Sorting

The process by which sediment grains are separated by size or density.

Stream Piracy

The capture of the headwaters of one stream by another stream.

Superposed Stream

A stream that maintains its course even as the underlying rock is deformed.

Suspended Load

Sediment that is carried within the water column of a stream.

Terrace

A flat, elevated area along a stream valley.

Transpiration

The release of water vapor from plants.

Trellis Pattern

A stream pattern in which tributaries join the main stream at right angles.

Turbulent Flow

Chaotic, swirling flow of water.

Ultimate Base Level

The lowest possible base level, which is sea level.

Waterfall

A cascade of water over a steep drop.

Water Gap

A gap in a ridge or mountain through which a stream flows.

Wind Gap

A gap in a ridge or mountain that is no longer occupied by a stream.

Yazoo Tributary

A tributary that flows parallel to the main stream for some distance before joining it.