Term
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Definition
| A fan-shaped deposit of sediment formed when a stream’s slope is abruptly reduced. |
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Term
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Definition
| Unconsolidated sediment deposited by a stream. |
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Term
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Definition
| A stream that continued to downcut and maintain its original course as an area along its course was uplifted by faulting or folding. |
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Term
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Definition
| A poorly drained area on a floodplain resulting when natural levees are present. |
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Term
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Definition
| Common term for sand and gravel deposits in a stream channel. |
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Term
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Definition
| The level below which a stream cannot erode. |
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Term
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Definition
| Sediment moved along the bottom of a stream by moving water. |
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Term
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Definition
| A stream consisting of numerous intertwining channels. |
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Term
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Definition
| The total amount of sediment a stream is able to transport. |
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Term
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Definition
| A measure of the largest particle a stream can transport; a factor dependent on velocity. |
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Term
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Definition
| The area of active erosion on the outside of a meander. |
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Term
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Definition
| A short channel segment created when a river erodes through the narrow neck of land between meanders. |
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Term
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Definition
| An accumulation of sediment formed where a stream enters a lake or an ocean. |
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Term
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Definition
| A stream system that resembles the pattern of a branching tree. |
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Term
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Definition
| The quantity of water in a stream that passes a given point in a period of time |
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Term
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Definition
| That portion of a stream’s load carried in solution. |
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Term
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Definition
| A section of a stream that leaves the main flow. |
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Term
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Definition
| An imaginary line that separates the drainage of two streams, often found along a ridge. |
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Term
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Definition
| The land area that contributes water to a stream. |
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Term
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Definition
| The overflow of a stream channel that occurs when discharge exceeds the channel’s capacity. |
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Term
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Definition
| The flat, low-lying portion of a stream valley subject to periodic inundation. |
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Term
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Definition
| A stream that has the correct channel characteristics to maintain exactly the velocity required to transport the material supplied to it. |
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Term
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Definition
| grade (slope) measured by the ratio of drop in a stream per unit distance, usually expressed as feet per mile |
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Term
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Definition
| The beginning or source area for a stream. Also called the headwaters. |
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Term
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Definition
| The extension upslope of the head of a valley due to erosion. |
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Term
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Definition
| Meandering channel that flows in a steep, narrow valley; formed either when an area is uplifted or when base level drops. |
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Term
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Definition
| The movement of surface water into rock or soil through cracks and pore spaces. |
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Term
|
Definition
| The maximum rate at which soil can absorb water. |
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Term
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Definition
| The movement of water particles in straight-line paths that are parallel to the channel. The water particles move downstream without mixing |
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Term
|
Definition
| The level of a lake, resistant rock layer, or any other base level that stands above sea level. |
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Term
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Definition
| A cross section of a stream channel along its descending course from the head to the mouth. |
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Term
|
Definition
| A loop-like bend in the course of a stream. |
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Term
|
Definition
| The point downstream where a river empties into another stream or water body. |
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Term
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Definition
| A curved lake produced when a stream cuts off a meander. |
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Term
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Definition
| A crescent-shaped accumulation of sand and gravel deposited on the inside of a meander. |
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Term
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Definition
| A depression formed in a stream channel by the abrasive action of the water’s sediment load. |
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Term
|
Definition
| A system of streams running in all directions away from a central elevated structure, such as a volcano. |
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Term
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Definition
| A drainage pattern characterized by numerous right angle bends that develop on jointed or fractured bedrock. |
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Term
|
Definition
| The average time interval between occurrences of hydrological events such as floods of a given or greater magnitude. |
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Term
|
Definition
| The average time interval between occurrences of hydrological events such as floods of a given or greater magnitude. |
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Term
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Definition
| Tiny channels that develop as unconfined flow begins producing threads of current. |
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Term
|
Definition
| Water that flows over the land rather than infiltrating into the ground. |
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Term
|
Definition
| Transportation of sediment through a series of leaps or bounces. |
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Term
|
Definition
| The speed at which a particle falls through a still fluid. |
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Term
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Definition
| Runoff moving in unconfined thin sheets. |
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Term
|
Definition
| The degree of similarity in particle size in sediment or sedimentary rock. |
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Term
|
Definition
| The diversion of the drainage of one stream, resulting from the headward erosion of another stream. |
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Term
|
Definition
| The channel, valley floor, and sloping valley walls of a stream. |
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Term
|
Definition
| 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. |
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Term
|
Definition
| The fine sediment carried within the body of flowing water or air. |
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Term
|
Definition
| A flat, bench-like structure produced by a stream, which was left elevated as the stream cut downward. |
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Term
|
Definition
| A system of streams in which nearly parallel tributaries occupy valleys cut in folded strata. |
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Term
|
Definition
| The movement of water in an erratic fashion often characterized by swirling, whirlpool-like eddies. |
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Term
|
Definition
| Sea level; the lowest level to which stream erosion could lower the land. |
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Term
|
Definition
| A pass through a ridge or mountain in which a stream flows. |
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Term
|
Definition
| A tributary that flows parallel to the main stream because a natural levee is present. |
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Term
|
Definition
| An elevated landform composed of alluvium that parallels some streams and acts to confine their waters, except during floodstage. |
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Term
|
Definition
| Rock or sediment through which groundwater moves easily. |
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Term
|
Definition
| An impermeable bed that hinders or prevents groundwater movement. |
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Term
|
Definition
| A well in which the water rises above the level where it was initially encountered. |
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Term
|
Definition
| A relatively narrow zone at the base of the zone of aeration. Here water rises from the water table in tiny, threadlike openings between grains of soil or sediment. |
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Term
|
Definition
| A naturally formed underground chamber or series of chambers most commonly produced by solution activity in limestone. |
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Term
|
Definition
| A cone-shaped depression in the water table immediately surrounding a well. |
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Term
|
Definition
| An equation stating that groundwater discharge depends on the hydraulic gradient, hydraulic conductivity, and cross-sectional area of an aquifer. |
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Term
|
Definition
| The difference in height between the bottom of a cone of depression and the original height of the water table. |
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Term
|
Definition
| Streams that again water from the inflow of groundwater through the streambed. |
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Term
|
Definition
| A fountain of hot water ejected periodically from the ground |
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Term
|
Definition
| Water in the zone of saturation. |
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Term
|
Definition
| The spring in which the water is 6 to 9 degrees Celsius (10 to 15 degrees Fahrenheit) warmer than the mean annual air temperature of its locality. |
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Term
|
Definition
| A factor relating to groundwater flow; it is a coefficient that takes into account the permeability of the aquifer and the viscosity of the fluid. |
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Term
|
Definition
| The slope of the water table. It is determined by finding the height difference between two points on the water table and dividing by the horizontal distance between the two points. |
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Term
|
Definition
| A type of topography formed on soluble rock (especially limestone) primarily by dissolution. It is characterized by sinkholes, caves, and underground drainage. |
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Term
|
Definition
| Stream that loses water to the groundwater system by outflow through the streambed. |
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Term
|
Definition
| A localized zone of saturation above the main water table, created by an impermeable layer. |
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Term
|
Definition
| A measure of a material’s ability to transmit water. |
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Term
|
Definition
| The volume of open spaces in rock or soil. |
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Term
|
Definition
| A depression produced in a region where soluble rock has been removed by groundwater. |
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Term
|
Definition
| A collective term for the dripstone features found in caverns. |
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Term
|
Definition
| A flow of groundwater that emerges naturally at the ground surface. |
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Term
|
Definition
| The icicle-like structure that hangs from the ceiling of a cavern. |
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Term
|
Definition
| The column-like form that grows upward from the floor of a cavern. |
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Term
|
Definition
| The area above the water table where openings in soil, sediment, and rock are not saturated but filled mainly with air. |
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Term
|
Definition
| The upper level of the saturated zone of groundwater. |
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Term
|
Definition
| An opening bored into the zone of saturation. |
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Term
|
Definition
| The zone where all open spaces in sediment and rock are completely filled with water. |
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Term
|
Definition
| A zone in which water is held as a film on the surface of soil particles and may be used by plants or withdrawn by evaporation. The uppermost subdivision of the unsaturated zone. |
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Term
|
Definition
| A general term for the loss of ice and snow from a glacier. |
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Term
|
Definition
| The grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, and ice. |
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Term
|
Definition
| A glacier confined to a mountain valley, which in most instances had previously been a stream valley. |
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Term
|
Definition
| A narrow, knifelike ridge separating two adjacent glaciated valleys. |
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Term
|
Definition
| A mechanism of glacial movement in which the ice mass slides over the surface below. |
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Term
|
Definition
| Wastage of a glacier that occurs when large pieces of ice break into the water. |
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Term
|
Definition
| An amphitheater-shaped basin at the head of a glaciated valley produced by frost wedging and plucking. |
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Term
|
Definition
| A pass between mountain valleys where the headwalls of two cirques intersect |
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Term
|
Definition
| A deep crack in the brittle surface of a glacier. |
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Term
|
Definition
| A streamlined symmetrical hill composed of glacial till. The steep side of the hill faces the direction from which the ice advanced. |
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Term
|
Definition
| A ridge of till marking a former position of the front of a glacier. |
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Term
|
Definition
| Sinuous ridge composed largely of sand and gravel deposited by a stream flowing in a tunnel beneath a glacier near its terminus. |
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Term
|
Definition
| A steep-sided inlet of the sea formed when a glacial trough was partially submerged. |
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Term
|
Definition
| Granular recrystallized snow. A transitional stage between snow and glacial ice. |
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Term
|
Definition
| The balance, or lack of balance, between ice formation at the upper end of a glacier, and ice loss in the zone of wastage. |
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Term
|
Definition
| An all-embracing term for sediments of glacial origin, no matter how, where, or in what shape they were deposited. |
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Term
|
Definition
| Scratches and grooves on bedrock caused by glacial abrasion. |
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Term
|
Definition
| A mountain alley that has been widened, deepened, and straightened by a glacier. |
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Term
|
Definition
| An undulating layer of till deposited as the ice front retreats. |
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Term
|
Definition
| A tributary valley that enters a glacial trough at a considerable height above the floor of the trough. |
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Term
|
Definition
| A pyramid-like peak formed by glacial action in three or more cirques surrounding a mountain summit. |
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Term
|
Definition
| A mass of glacial ice covering a high upland or plateau and spreading out radially. |
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Term
|
Definition
| A very large, thick mass of glacial ice flowing outward in all directions from one or more accumulation centers. |
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Term
|
Definition
| A steep-sided hill composed of sand and gravel, originating when sediment collected in openings in stagnant glacial ice. |
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Term
|
Definition
| A narrow, terrace-like mass of stratified drift deposited between a glacier and an adjacent valley wall. |
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Term
|
Definition
| A ridge of till along the sides of a valley glacier composed primarily of debris that fell to the glacier from the valley walls. |
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Term
|
Definition
| A ridge of till formed when lateral moraines from two coalescing alpine glaciers join. |
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Term
|
Definition
| A relatively flat, gently sloping plain consisting of materials deposited by meltwater streams in front of the margin of an ice sheet. |
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Term
|
Definition
| A chain of small lakes in a glacial trough that occupies basins created by glacial erosion. |
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Term
|
Definition
| A type of glacial movement that occurs within the glacier, below a depth of approximately 50 meters, in which the ice is not fractured. |
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Term
|
Definition
| A lake formed during a period of increased rainfall. |
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Term
|
Definition
| An end moraine formed as the ice front stagnated during glacial retreat. |
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Term
|
Definition
| An asymmetrical knob of bedrock formed when glacial abrasion smoothes the gentle slope facing the advancing ice sheet and plucking steepens the opposite side as the ice overrides the know. |
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Term
|
Definition
| Frozen seawater that is associated with Polar Regions. |
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Term
|
Definition
| The lower limit of perennial snow. |
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Term
|
Definition
| Sediments deposited by glacial meltwater. |
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Term
|
Definition
| A period of rapid glacial advance. |
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Term
|
Definition
| A small lake in a cirque. |
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Term
|
Definition
| The end moraine marking the farthest advance of a glacier. |
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Term
|
Definition
| Unsorted sediment deposited directly by a glacier. |
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Term
|
Definition
| A rock formed when glacial till is lithified. |
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Term
|
Definition
| Triangular-shaped cliff produced when a spur of land that extends into a valley is removed by the great erosional force of a valley glacier. |
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Term
|
Definition
| A glacier confined to a mountain valley, which in most instances had previously been a stream valley. |
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Term
|
Definition
| A relatively narrow body of stratified drift deposited on a valley floor by meltwater streams that issue from the terminus of an alpine glacier. |
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Term
|
Definition
| The part of a glacier characterized by snow accumulation and ice formation. The outer limit of this zone is the snowline. |
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Term
|
Definition
| The upper portion of a glacier consisting of brittle ice. |
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Term
|
Definition
| The part of a glacier beyond the snowline where annually there is a net loss of ice. |
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Term
|
Definition
| An ice-transported boulder that was not derived from the bedrock near its present site. |
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Term
|
Definition
| Depression created when blocks of ice become lodged in glacial deposits and subsequently melt. |
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Term
|
Definition
| The process by which pieces of bedrock are lifted out of place by a glacier. |
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Term
|
Definition
| Ground-up rock produced by the grinding effect of a glacier. |
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Term
|
Definition
| An apron of sediment along a mountain front created by the coalescence of alluvial fans. |
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Term
|
Definition
| A solitary sand dune shaped like a crescent with its tips pointing downwind. |
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Term
|
Definition
| Particles moved along the ground surface by wind. |
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Term
|
Definition
| A depression excavated by wind in easily eroded materials. |
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Term
|
Definition
| Structure in which relatively thin layers are inclined at an angle to the main bedding. Formed by currents of wind. |
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Term
|
Definition
| The lifting and removal of loose material by wind. |
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Term
|
Definition
| One of the two types of dry climate: the driest of the dry climates. |
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Term
|
Definition
| A layer of coarse pebbles and gravel created when wind removed the finer material. |
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Term
|
Definition
| Ecosystem degradation of marginal areas, brought about by human activities. |
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Term
|
Definition
| Hill or ridge of wind-deposited sand. |
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Term
|
Definition
| A stream that is usually dry because it carries water only in response to specific episodes of rainfall. |
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Term
|
Definition
| An isolated mountain remnant characteristic of the late stage of erosion in a mountainous arid region. |
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Term
|
Definition
| A discontinuous pattern of intermittent streams that do not flow to the ocean. |
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Term
|
Definition
| Deposits of windblown silt, lacking visible layers, generally buff-colored, and capable of maintaining a nearly vertical cliff. |
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Term
|
Definition
| Long ridges of sand oriented parallel to the prevailing wind; these dunes form where sand supplies are limited. |
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Term
|
Definition
| A sand dune similar in shape to a barchan dune except that its tips point into the wind. These dunes often form along coasts that have strong onshore winds, abundant sand, and vegetation that partly covers the sand. |
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Term
|
Definition
| A temporary lake in a playa. |
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Term
|
Definition
| A dry area on the lee side of a mountain range. |
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Term
|
Definition
| Transportation of sediment through a series of leaps or bounces. |
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Term
|
Definition
| The steep, leeward surface of a sand dune that maintains a slope of about 34 degrees. |
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Term
|
Definition
| An isolated hill of sand that exhibits a complex form and develops where wind directions are variable. |
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Term
|
Definition
| One of the two types of dry climate. A marginal and more humid variant of the desert that separates it from bordering humid climates. |
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Term
|
Definition
| The fine sediment carried within the body of flowing air. |
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Term
|
Definition
| A series of long ridges oriented at right angles to the prevailing wind; these dunes form where vegetation is sparse and sand is very plentiful. |
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Term
|
Definition
| A cobble or pebble polished and shaped by the sandblasting effect of wind. |
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Term
|
Definition
| A streamlined, wind-sculpted ridge having the appearance of an inverted ship’s hull that is oriented parallel to the prevailing wind. |
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Term
|
Definition
| The flat central area of an undrained desert basin. |
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Term
|
Definition
| The grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, and ice. |
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Term
|
Definition
| The inner portion of the shore, lying landward of the high-tide shoreline. It is usually dry, being affected by waves only during storms. |
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Term
|
Definition
| A low, elongate ridge of sand that parallels the coast. |
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Term
|
Definition
| A sandbar that completely crosses a bay, sealing it off from the main body of water. |
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Term
|
Definition
| An accumulation of sediment found along the landward margin of the ocean or a lake. |
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Term
|
Definition
| The transport of sediment in a zigzag pattern along a beach, caused by the uprush of water from obliquely breaking waves. |
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Term
|
Definition
| The wet, sloping surface that extends from the berm to the shoreline. |
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Term
|
Definition
| Process in which large quantities of sand are added to the beach system to offset losses caused by wave erosion. |
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Term
|
Definition
| The dry, gently sloping zone on the backshore of a beach at the foot of the coastal cliffs or dunes. |
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Term
|
Definition
| A structure protecting a nearshore area from breaking waves. |
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Term
|
Definition
| A strip of land that extends inland from the coastline as far as ocean-related features can be found. |
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Term
|
Definition
| The coast’s seaward edge. The landward limit of the effect of the highest storm waves on the shore. |
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Term
|
Definition
| The movement of tidal current away from the shore. |
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Term
|
Definition
| A coast where land formerly below sea level has been exposed by crustal uplift or a drop in sea level or both. |
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Term
|
Definition
| A funnel-shaped inlet of the sea that formed when a rise in sea level or subsidence of land caused the mouth of a river to be flooded. |
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Term
|
Definition
| The distance that the wind has traveled across the open water. |
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Term
|
Definition
| The tidal current associated with the increase in the height of the tide. |
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Term
|
Definition
| That portion of the shore lying between the normal high and low water marks; the intertidal zone. |
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Term
|
Definition
| A short wall built at a right angle to the seashore to trap moving sand. |
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Term
|
Definition
| Structures built to protect a coast from erosion or to prevent the movement of sand along a beach. |
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Term
|
Definition
| A pair of structures extending into the ocean at the entrance to a harbor or river that are built for the purpose of protection against storm waves and sediment deposition. |
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Term
|
Definition
| A nearshore current that flows parallel to the shore |
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Term
|
Definition
| A wave-cut platform uplifted above sea level by tectonic forces. |
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Term
|
Definition
| The lowest tidal range, occurring near the times of the first and third quarters of the moon. |
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Term
|
Definition
| The zone of a beach that extends from the low-tide shoreline seaward to where waves break at low tide. |
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Term
|
Definition
| The relatively flat submerged zone that extends from the breaker line to the edge of the continental shelf. |
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Term
|
Definition
| An arch formed by wave erosion when caves on opposite sides of a headland unite. |
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Term
|
Definition
| An isolated mass of rock standing just offshore, produced by wave erosion of a headland. |
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Term
|
Definition
| A barrier constructed to prevent waves from reaching the area behind the wall; to defend property from the force of breaking waves. |
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Term
|
Definition
| A coast whose form is largely the result of the partial drowning of a former land surface due to a rise of sea level or subsidence of the crust, or both. |
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Term
|
Definition
| A fold in sedimentary strata that resembles an arch. |
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Term
|
Definition
| A circular downfolded structure. |
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Term
|
Definition
| The loss of strength by a material usually in the form of sudden fracturing. |
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Term
|
Definition
| The loss of strength by a material usually in the form of sudden fracturing. |
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Term
|
Definition
| Differential stress that shortens a rock body. |
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Term
|
Definition
| General term for the processes of folding, faulting, shearing, compression, or extension of rocks as the result of various natural forces. |
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Term
|
Definition
| A nearly horizontal fault that may extend for hundreds of kilometers below the surface. |
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Term
|
Definition
| Forces that are unequal in different direction. |
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Term
|
Definition
| The angle at which a rock layer or fault is inclined from the horizontal (dip is perpendicular to strike). |
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Term
|
Definition
| A fault in which the movement is parallel to the dip of the fault. |
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Term
|
Definition
| A roughly circular upfolded structure. |
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Term
|
Definition
| A type of solid-state flow that produces a change in the size and shape of a rock body without fracturing. |
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Term
|
Definition
| A break in a rock mass along which movement has occurred. |
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Term
|
Definition
| A mountain formed by the displacement of rock along a fault. |
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Term
|
Definition
| a small step on the ground surface where one side of a fault has moved vertically with respect to another |
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Term
|
Definition
| A bent layer or series of layers that were originally horizontal and subsequently deformed. |
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Term
|
Definition
| That which tends to put stationary objects in motion or change motions of moving bodies. |
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Term
|
Definition
| A valley formed by the downward displacement of a fault-bounded block. |
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Term
|
Definition
| A narrow, sharp-crested ridge formed by the upturned edge of a steeply dipping bed of resistant rock. |
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Term
|
Definition
| An elongate, uplifted block of crust bounded by faults. |
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Term
|
Definition
| A fracture in rock along which there has been no movement. |
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Term
|
Definition
| A remnant or outlier of a thrust sheet that was isolated by erosion. |
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Term
|
Definition
| A one-limbed flexure in strata. |
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Term
|
Definition
| A fault in which the rock above the fault plane has moved down relative to the rock below (hanging wall has moved down; footwall has moved up). |
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Term
|
Definition
| A fault in which the rock above the fault plane has moved up relative to the rock below (hanging wall has moved up; footwall has moved down). |
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Term
|
Definition
| All features created by the processes of deformation from minor fractures in bedrock to a major mountain chain. |
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Term
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Definition
| Stress that causes two adjacent parts of a body to slide past one another. |
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Definition
| An irreversible change in the shape and size of a rock body caused by stress. |
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Definition
| The force per unit area acting on any surface within a solid. |
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Definition
| A fault along which the movement is horizontal. |
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Definition
| A linear downfold in sedimentary strata; the opposite of anticline. |
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Definition
| The type of stress that tends to pull a body apart. |
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Definition
| A low-angle reverse fault. |
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Definition
| A boundary in which two plates slide past one another without creating or destroying lithosphere. |
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Definition
| The compass direction of the line of intersection created by a dipping bed or fault and a horizontal surface. |
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Definition
| A smaller earthquake that follows the main earthquake. |
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Definition
| A seismic wave that travels through Earth’s interior. |
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Term
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Definition
| Vibration of Earth produced by the rapid release of energy. |
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Term
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Definition
| The sudden release of stored strain in rocks that results in movement along a fault. |
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Definition
| The location of Earth’s surface that lies directly above the focus of an earthquake. |
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Term
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Definition
| A break in a rock mass along which movement has occurred. |
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Definition
| Gradual displacement along a fault. |
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Definition
| The zone within Earth where rock displacement produces an earthquake. |
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Term
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Definition
| Small earthquake that often precedes a major earthquake. |
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Term
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Definition
| The zone within Earth where rock displacement produces an earthquake. |
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Term
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Definition
| Objects at rest tend to remain at rest, and objects in motion tend to stay in motion unless either is acted upon by an outside force. |
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Term
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Definition
| A measure of the degree of earthquake shaking at a given locale based on the amount of damage. |
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Term
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Definition
| The transformation of a stable soil into a fluid that is often unable to support buildings or other structures. |
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Term
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Definition
| These earthquake-generated waves travel along the outer layer of Earth and are responsible for most of the surface damage. |
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Term
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Definition
| An estimate of the total amount of energy released during an earthquake, based on seismic records. |
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Term
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Definition
| ccur at subduction zones at destructive plate boundaries (convergent boundaries), where one tectonic plate is subducted (forced underneath) by another. |
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Term
| Modified Mercalli Intensity Scale |
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Definition
| A 12-point scale developed to evaluate earthquake intensity based on the amount of damage to various structures. |
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Term
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Definition
| A more precise measure of earthquake magnitude than the Richter scale that is derived from the amount of displacement that occurs along a fault zone. |
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Term
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Definition
| A type of seismic wave that involves alternating compression and expansion of the material through which it passes. |
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Definition
| A scale of earthquake magnitude based on the amplitude of the largest seismic wave. |
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Definition
| A type of seismic wave that involves oscillation perpendicular to the direction of propagation. |
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Definition
| A segment of an active fault zone that has not experienced a major earthquake over a span when most other segments have. |
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Definition
| A rapidly moving ocean wave generated by earthquake activity, which is capable of inflicting heavy damage in coastal regions. |
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Term
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Definition
| part of the Earth’s mantle, and is located between the lower mantle and the upper mantle, between a depth of 410 and 660 km. |
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Term
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Definition
| The record made by a seismograph. |
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Term
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Definition
| An instrument that records earthquake waves. |
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Term
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Definition
| The study of earthquakes and seismic waves. |
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Term
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Definition
| Seismic waves that travel along the outer layer of Earth. |
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Term
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Definition
| The Japanese word for a seismic sea wave. |
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Definition
| A subdivision of the mantle situated below the lithosphere, in which the rock is easily deformed. |
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Term
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Definition
| The transfer of heat through matter by molecular activity. |
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Term
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Definition
| The transfer of heat by the mass movement or circulation of a substance. |
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Term
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Definition
| The innermost layer of Earth based on composition. It is thought to be largely an iron-nickel alloy with minor amounts of oxygen, silicon, and sulfur. |
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Term
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Definition
| The very thin outermost layer of Earth. |
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Term
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Definition
| A region in roughly the lowermost 200 kilometers of the mantle where P-waves experience a sharp decrease in velocity. |
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Term
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Definition
| The gradual increase in temperature with depth in the crust. |
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Term
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Definition
| The gradual increase in temperature with depth in the crust. |
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Term
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Definition
| The solid innermost layer of Earth, about 1216 kilometers (754 miles) in radius. |
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Term
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Definition
| The part of the mantle that extends from the core-mantle boundary to a depth of 660 kilometers. Also known as mesosphere. |
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Term
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Definition
| One of Earth’s compositional layers. The solid rocky shell that extends from the base of the crust to a depth of 2900 kilometers. |
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Term
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Definition
| The boundary separating the crust and the mantle, discernible by an increase in seismic velocity (Mohorovicic discontinuity). |
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Term
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Definition
| A layer beneath the mantle about 2270 kilometers (1410 miles) thick, which has the properties of a liquid. |
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Term
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Definition
| a part of the Earth's mantle located between the lower mantle and the upper mantle |
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Term
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Definition
| A measure of a fluid’s resistance to flow. |
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Term
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Definition
| The rigid outer layer of Earth, including the crust and upper mantle. |
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Term
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Definition
| A subdivision of the mantle situated below the lithosphere, in which rock is easily deformed. |
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Term
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Definition
| A hypothesis, credited largely to Alfred Wegener, that suggested all present continents once existed as a single supercontinent. Further, beginning about 200 million years ago, the supercontinent began breaking into smaller continents, which then “drifted” to their present positions. |
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Term
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Definition
| Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. |
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Term
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Definition
| A boundary in which two plates move together, resulting in oceanic lithosphere being thrust beneath an overriding plate, eventually to be reabsorbed into the mantle. It can also involve the collision of two continental plates to create a mountain system. |
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Term
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Definition
| The temperature above which a material loses its magnetization. |
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Term
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Definition
| A narrow, elongated depression of the seafloor. |
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Term
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Definition
| A boundary in which two plates move apart, resulting in upwelling of material from the mantle to create new seafloor. |
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Definition
| The natural remnant magnetism in rock bodies. |
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Term
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Definition
| Linear zone of irregular topography on the deep-ocean floor that follows transform faults and their inactive extensions. |
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Term
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Definition
| A magnetic field opposite to that which presently exists. |
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Term
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Definition
| A concentration of heat in the mantle, capable of producing magma that in turn extrudes onto Earth’s surface. |
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Term
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Definition
| A chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another. |
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Term
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Definition
| The rigid outer layer of Earth, including the crust and upper mantle. |
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Term
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Definition
| A coherent unit of Earth’s rigid outer layer that includes the crust and upper unit. |
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Term
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Definition
| Relative time scale based on the pattern of normal and reverse polarity preserved in the rock record. May be made numeric when basalts are radiometrically dated. |
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Term
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Definition
| A mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core-mantle boundary. |
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Term
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Definition
| A magnetic field the same as that which presently exists. |
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Term
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Definition
| The natural remnant magnetism in rock bodies. |
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Term
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Definition
| The proposed supercontinent that 200 million years ago began to break apart and form the present landmasses. |
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Term
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Definition
| The process by which most igneous rocks melt. Since individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results. |
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Term
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Definition
| A coherent unit of Earth’s rigid outer layer that includes the crust and upper unit. |
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Term
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Definition
| The theory that proposes that Earth’s outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself. |
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Term
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Definition
| A magnetic field opposite to that which presently exists. |
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Term
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Definition
| A mechanism that may contribute to plate motion. It involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity. |
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Term
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Definition
| A linear zone in which plates move away from each other. |
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Term
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Definition
| A long, narrow trough bounded by normal faults, representing a region where divergence is taking place. |
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Term
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Definition
| The hypothesis first proposed in the 1960s by Harry Hess, which suggested that new oceanic crust is produced at the crests of mid-ocean ridges, which are the sites of divergence. |
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Term
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Definition
| a mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and pulls the trailing lithosphere along |
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Term
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Definition
| one of the driving forces of plate motion, it arises from the drag of the subducting plate on the adjacent mantle. It is an induced mantle circulation that pulls both the subducting and overriding plates toward the trench |
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Term
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Definition
| A boundary in which two plates move apart, resulting in upwelling of material from the mantle to create new seafloor. |
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Term
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Definition
| A fault along which the movement is horizontal. |
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Term
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Definition
| A long, narrow zone where one lithospheric plate descends beneath another. |
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Term
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Definition
| A coherent unit of Earth’s rigid outer layer that includes the crust and upper unit. |
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Term
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Definition
| A major strike-slip fault that cuts through the lithosphere and accommodates motion between two plates. |
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Term
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Definition
| A boundary in which two plates slide past one another without creating or destroying lithosphere. |
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Term
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Definition
| a chain of volcanic islands generally located a few hundred kilometers from a trench where there is an active subduction of one oceanic plate beneath another |
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Term
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Definition
| Very level area of the deep-ocean floor, usually lying at the foot of the continental rise. |
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Term
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Definition
| A large wedge-shaped mass of sediment that accumulates in subduction zones. Here sediment is scraped from the subducting oceanic plate and accreted to the overriding crustal block. |
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Term
| Active continental margin |
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Definition
| Usually narrow and consisting of highly deformed sediments. Such margins occur where oceanic lithosphere is being subducted beneath the margin of a continent. |
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Term
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Definition
| Hydrothermal vents on the ocean floor that emit a black cloud of hot, metal-rich water. |
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Term
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Definition
| Subduction in which the angle of descent is small because the oceanic lithosphere is still warm and buoyant. It occurs where a spreading center is near a subduction zone. |
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Term
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Definition
| That portion of the seafloor adjacent to the continents. |
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Term
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Definition
| A linear zone along which continental lithosphere stretches and pulls apart. Its creation may mark the beginning of a new ocean basin. |
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Term
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Definition
| The portion of seafloor that lies between the continental margin and the oceanic ridge system. |
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Term
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Definition
| A submerged, flat-topped seamount. |
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Term
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Definition
| A continuous mountainous ridge on the floor of all the major ocean basins and varying in width from 500-5000 kilometers (300-3000 miles), and representing divergent plate boundaries. |
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Term
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Definition
| An extensive region on the ocean floor composed of thick accumulations of pillow basalts and other mafic rocks that in some cases exceed 30 kilometers in thickness. |
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Term
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Definition
| The sequence of rocks that make up the oceanic crust. The three-layer sequence includes an upper layer of pillow basalts, a middle zone of sheeted dikes, and a lower layer of gabbro. |
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Term
| Passive continental margin |
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Definition
| A margin that consists of a continental shelf, continental slope, and continental rise. They are not associated with plate boundaries and therefore experience little volcanism and few earthquakes. |
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Term
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Definition
| A continuous mountainous ridge on the floor of all the major ocean basins and varying in width from 500-5000 kilometers (300-3000 miles), and representing divergent plate boundaries. |
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Term
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Definition
| Basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows. |
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Term
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Definition
| An isolate volcanic peak that rises at least 1000 meters (3300 feet) above the deep-ocean floor. |
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Term
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Definition
| A large group of nearly parallel dikes. |
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Term
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Definition
| A large wedge-shaped mass of sediment that accumulates in subduction zones. Here sediment is scraped from the subducting oceanic plate and accreted to the overriding crustal block. |
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Term
| Andean-type plate margins |
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Definition
| Convergent plate boundaries that generate continental volcanic arcs. |
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Term
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Definition
| A basin that forms on the side of a volcanic arc away from the trench. |
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Term
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Definition
| Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. |
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Term
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Definition
| Mountains formed by the displacement of rock along faults. |
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Term
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Definition
| Regions within compressional mountain systems where large areas have been shortened and thickened by the processes of folding and thrust faulting. |
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Term
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Definition
| The region located between a volcanic arc and an accretionary wedge where shallow-water marine sediments typically accumulate. |
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Term
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Definition
| The gradual subsidence of mountains caused by lateral spreading of weak material located deep within these structures. |
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Term
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Definition
| A chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another. |
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Term
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Definition
| The concept that Earth’s crust is “floating” in gravitational balance upon the material of the mantle. |
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Term
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Definition
| Compensation of the lithosphere when weight is added or removed. When weight is added, the lithosphere will respond by subsiding, and when weight is removed, there will be uplift. |
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Term
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Definition
| Relatively small fragment of continental crust that may lie above sea level or submerged. |
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Term
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Definition
| The processes that collectively result in the formation of mountains. |
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Term
| Passive continental margin |
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Definition
| A margin that consists of a continental shelf, continental slope, and continental rise. They are not associated with plate boundaries and therefore experience little volcanism and few earthquakes. |
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Term
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Definition
| The zone along which two crustal fragments are joined together. |
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Term
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Definition
| A crustal block bounded by faults, whose geologic history is distinct from the histories of adjoining crustal blocks. |
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Term
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Definition
| A chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another |
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Term
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Definition
| A mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core-mantle boundary. |
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