physical geology exam 2 vocab

hypothesis

a tentative explanation that is then tested to determine if it is valid

theory

a well-tested and widely accepted view that explains certain observable facts

scientific method

the process by which researchers raise questions, gather data, and formulate and test scientific hypotheses

hydrosphere

the water portion of our planet; one of the traditional subdivisions of earth’s physical environment

atmosphere

the gaseous portion of a planet, the planet’s envelope of air. one of the traditional subdivisions of earth’s physical environment

biosphere

the totality of life-forms on earth

geosphere

the solid earth; one of earth’s four basic spheres

earth system science

an interdisciplinary study that seeks to examine earth as a system composed of numerous interacting parts or subsystems

system

a group of interacting or independent parts that form a complex whole

soil

a combination of mineral and organic matter, water, and air; the portion of the regolith that supports plant growth

soil texture

the relative proportions of clay, silt, and sand in a soil. a soil’s texture strongly influences its ability to retain and transmit water and air

regolith

the layer of rock and mineral fragments that nearly everywhere covers earth’s land surface

humus

organic matter in soil that is produced by the decomposition of plants and animals

parent material

the material on which a soil develops

plant photosynthesis

the production of energy-rich molecules of sugar from molecules of carbon dioxide (co2) and water (h2o) using sunlight as the energy source

great oxygenation event

a time about 2.5 billion years ago, when a significant amount of oxygen appeared in the atmosphere

outgassing

the escape of dissolved gases from molten rocks

banded iron formation

a finely layered iron and silica-rich (chert) layer deposited mainly during the precambrian

weathering

the disintegration and decomposition of rock at or near the surface of earth

mechanical weathering

the physical disintegration of rock, resulting in smaller fragments

chemical weathering

the process by which the internal structure of a mineral is altered by the removal and/or addition of elements

erosion

the incorporation and transportation of material by a mobile agent, such as water, wind, or ice

joint

a fracture in rock along which there has been no movement

exfoliation dome

a large, dome-shaped structure, usually composed of granite, that is formed by sheeting

frost wedging

the mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices

sheeting

a mechanical weathering process that is characterized by the splitting off of slablike sheets of rock

oxidation

the removal of one or more electrons from an atom or ion. so named because elements commonly combine with oxygen

spheroidal weathering

any weathering process that tends to produce a spherical shape from an initially blocky shape

dissolution

the process of dissolving into a homogenous solution, as when an acidic solution dissolves limestone; a common form of chemical weathering

hydrolysis

a chemical weathering process in which minerals are altered by chemically reacting with water and acid

differential weathering

the variation in the rate and degree of weathering caused by such factors as mineral makeup, degree of jointing, and climate

hydrologic cycle

the unending circulation of earth’s water supply. the cycle is powered by energy from the sun and is characterized by continuous exchanges of water among the oceans, the atmosphere, and the continents

infiltration

the movement of surface water into rock or soil through cracks and pore spaces

evapotranspiration

the combined effect of evaporation and transpiration

runoff

water that flows over land rather than infiltrating into the ground

headward erosion

the extension upslope of the head of a valley due to erosion

watergap

a pass through a ridge or mountain in which a stream flows

stream

a general term to denote the flow of water within any channel. thus, a small creek and a large river are both streams

dendritic pattern

a stream system that resembles the pattern of a branching tree

antecedent stream

a stream that continued to downcut and maintain its original course as an are

river

a general term for a stream that carries a substantial amount of water and has numerous tributaries

radical pattern

a system of streams running in all directions, away from a central elevated structure, such as a volcano

superposed stream

a stream that cuts through a ridge lying across its path. the stream established its course on uniform layers at a higher level without regard to underlying structures and subsequently downcut

drainage basin

the land area that contributes water to a stream. also called a watershed

rectangular pattern

a drainage pattern characterized by numerous right angle bends that develops on jointed or fractured bedrock

divide

an imaginary line that separates the drainage of two streams, often found along a ridge

trellis pattern

a system of streams in which nearly parallel tributaries occupy valleys cut enfolded strata

gradient

the slop of a stream, generally expressed as the vertical drop over a fixed distance

longitudinal profile

a cross section of a stream channel along its descending course from the head to the mouth

laminar flow

the movement of water particles in straight-line paths that are parallel to the channel. the water particles move downstream without mixing

wetted perimeter

the total distance in a linear cross-section of a stream that is in contact with water

head (stream)

the beginning or source area for a stream. also called headwaters

turbulent flow

erratic movement of watering a stream that passes a given point in a period of time

discharge

the quantity of water often characterized by swirling, whirlpool-like eddies. most streamflow is of this type

mouth

the point downstream where a river empties into another stream or water body

quarrying

removing loosened blocks from the bed of a channel

dissolved load

the portion of a stream’s load that is carried in solution

capacity

the total amount of sediment that a stream is able to transport

competence

a measure of the largest particle a stream can transport; a factor dependent on velocity

suspended load

fine sediment carried within the body of flowing water or air

abrasion

the grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, and ice

bed load

sediment moved along the bottom of a stream by moving water, or particles moved along the ground surface by wind

sorting

the degree of similarity in particle size in sediment or sedimentary rock

pothole

a depression formed in a stream channel by the abrasive action of the water’s sediment load

settling velocity

the speed at which a particle falls through a still fluid. the size, shape, and specific gravity of particles influence settling velocity

alluvium

unconsolidated sediment deposited by a stream

corrosion

the process by which soluble rock is gradually dissolved by flowing water

saltation

transportation of sediment through a series of leaps or bounces

bedrock channel

a channel in which a stream is cutting into solid rock. such channels typically form in the headwaters or river systems where gradients are high.

alluvial channel

a stream channel in which the bed and banks are composed largely of unconsolidated sediment (alluvium) that was previously deposited in the valley

meander

a loop like bend in the course of a stream

cut bank

the area of active erosion on the outside of a meandr

point bar

a crescent-shaped accumulation of sand and gravel deposited on the inside of a meander

cutoff

a short channel segment created when a river erodes through the narrow neck of land between meanders

oxbow lake

a curved lake that is created when a stream cuts off a meander

braided channel

a stream channel that is interwoven with other stream channels. such channels form where a large portion of a stream’s sediment load consists of coarse material (sand and gravel) and the stream has a highly variable discharge

stream valley

the channel, valley floor, and sloping valley walls of a stream

base level

the level below which a stream cannot erode

ultimate base level

sea level; the lowest level to which stream erosion could lower the land

local base level

the level of a lake, resistant rock layer, or any other base level that stands above sea level. also called temporary base level

graded stream

a stream that has the correct channel characteristics to maintain exactly the velocity required to transport the material supplied to it.

downcutting

the lowering of a stream bed toward base level as turbulent water lifts unconsolidated material or when bedrock channels are lowered by means of quarrying, abrasion, and corrosion

floodplain

the flat, low-lying portion of a stream valley subject to periodic inundation

incised meander

a meandering channel that flows in a steep, narrow valley. it forms either when an area is uplifted or when the base level drops

terrance

a flat, bench-like structure produced by a stream, which was left elevated as the stream cut downward

beach

an accumulation of sediment found along the landward margin of the ocean or a lake

wave refraction

a change in direction of waves as they enter shallow water. the portion of the wave in shallow water is slowed, which causes the waves to bend and align with the underwater contours

beach drift

the transport of sediment in a zigzag pattern along a beach, caused by the uprush of water from obliquely breaking waves

longshore current

a stream that loses water to the groundwater system by outflow through the steam bed.

rip current

a strong, narrow surface or near-surface current of short duration and high speed that moves seaward through the breaker zone at nearly a right angle to the shore.

wave-cut cliff

a seaward-facing cliff along a steep shoreline formed by wave erosion at its base and mass wasting

wave-cut platform

a bench of shelf along a shore at sea level, cut by wave erosion

marine terrance

a wave-cut platform that has been exposed above sea level

sea arch

an arch formed by wave erosion when caves on opposite sides of a headland unite

sea stack

an isolated mass of rock standing just offshore, produced by wave erosion of a headland

spit

an elongate ridge of sand that projects from the land into the mouth of an adjacent bay

badmouth bar

a sandbar that completely crosses a bay, sealing it off from the main body of water

barrier island

a low, elongate ridge of sand that parallels the coast

tombolo

a ridge of sand that connects an island to the mainland or to another island