Chapter 14 The Internal Processes

Plate Tectonics
Seafloor spreading- this theory said that midocean ridges are formed by currents of magma rising up from the mantle; volcanic eruptions create new basaltic ocean floor, that then spreads away literally from the ridge.
Subduction- a process when older lithosphere descends into the asthenosphere where it is ultimately “recycled.”

Verification of Seafloor Spreading
Paleomagnetisim- used to test the theory of seafloor spreading by studying paleomagnetic data from a portion of the mid-ocean ridge system
Ocean floor core samples- indicated that sediments farthest from the ridges are oldest

The continents are embedded in the thicker lithosphere plates, carried along by the action of seafloor spreading

Divergent Boundaries
Divergent boundary- magma from the asthenosphere wells up in the opening between plates
	•	said to be constructive because material is being added to the crustal surface at such locations
Continental rift valley- when divergent boundaries develop within a continent

Convergent Boundaries
Convergent boundary- plates collide and as such are sometimes called destructive boundaries because they result in removal or compression of the surface crust
	•	convergent plate boundaries are responsible for some of the most massive and spectacular of earthly landforms
	•	Oceanic-continental convergence: a mountain range is formed on land and a parallel deep oceanic trench develops as the seafloor is pulled down by the subducting plate.
	•	Oceanic-oceanic convergence: if the convergent boundary is between two oceanic plates, subduction also takes place
	•	With time, a volcanic island arc develops
	•	Continental- continental convergence: no subduction takes place because continental crust is too buoyant to subduct
	•	Instead, huge mountain ranges are built up

Transform Boundaries
Transform boundary- two plates slip past one another laterally
	•	this slippage occurs along great vertical fractures called transform faults



The Pacific Ring of Fire
Pacific ring of fire- along these plate boundaries many volcanoes and earthquakes take place

Additions to the Basic Plate Tectonics Theory
Mantle plumes- spots of volcanic activity in the interior of a plate
	•	believed to be relatively stationary over long periods of time

Accreted Terranes
Terrane- a small-to-medium mass of lithosphere that may have been carried a long distance by a drifting plate that eventually converges with another plate

Vulcanism
Vulcanism- a general term that refers to all the phenomena connected with the origin and movement of molten rock
Magma- molten material below the surface
Lava- when magma is extruded onto Earth’s surface
Pyroclastic material- outward flow of lava, such as solid matter as rock fragments, solidified lava blobs, ashes, and dust

Volcano Disruption
A volcano is considered active if it has erupted at least once within historical times and is considered likely to do so again

Lava Flows
Flood basalt- applied to the vast accumulations of lava that build up, layer upon layer, sometimes covering tens of thousands of square kilometers to depths of many hundreds of meters

Shield Volcanoes
Shield volcanoes- built up of layer upon layer of solidified lava flows with relatively little pyroclastic material

Composite Volcanoes- volcanoes that emit higher silica “intermediate” lavas such as andesite often erupt explosively and tend to develop into symmetrical, steep-sided volcanoes

Lava Domes- have masses of very viscous lava such as high-silica rhyolite that are too thick and pasty to flow very fast

Cinder Cones- the smallest of the volcanic mountains
	•	cone shaped peaks built by the pyroclastic materials that are ejected from the volcanic vent



Calderas- produced when a volcano explodes, collapses, or does both
	•	results in an immense basin-shaped depression, generally circular, that has a diameter many times larger than that of the original volcanic vent or vents

Volcanic Gases
	•	water vapor makes up the bulk of the gas emitted, but other volcanic fluorine

Lava Flows- can produce significant property damage
	- the speed and distance covered by a lava flow depends mostly on its viscosity, which in turn depends on its silica content

Pyroclastic Flows- terrifying high speed avalanche of searing hot gases, ash, and rock fragments
	•	can travel down a volcano at speeds of more than 160 kilometers per hour, burning and burying everything in its path

Igneous Features
Igneous intrusion- if the igneous rock is pushed upward into the crust either before or after solidification

Batholiths- the largest and most amorphous intrusion, a subterranean igneous body of indefinite depth and enormous size

Stocks- amorphous and of indefinite depth

Laccoliths- produced when slow-flowing, viscous magma is forced between horizontal layers of preexisting rock

Dikes- a vertical or nearly vertical sheet of magma thrust upward into preexisting rock, sometimes forcing its way into vertical fractures and sometimes melting its way upward

Sills- a long, thin intrusive body whose orientation is determined by the structure of the preexisting rocks
	•	formed when magma is forced between strata that are already in place; the result is often a horizontal igneous sheet between horizontal sedimentary layers

Veins- formed when molten material forces itself into small fractures in the preexisting rocks, but they can also result from melting by an upward surge of magma

Diastrophism- a general term that refers to the deformation of Earth’s crust

Folding- when crustal rocks are subjected to certain forces, particularly lateral compression, they are often deformed by being bent

Anticline- simple symmetrical upfold

Syncline- simple downfold

Overturned fold- an upfold that has been pushed so vigorously from one side that it becomes over steepened enough to have a reverse orientation on the other side

Faulting- when rock is broken with accompanying displacement
Fault scarps- steep cliffs that represent the edge of a vertically displaced block

Types of Faults
	•	Normal faults: results from tension stresses in the crust; produces a very steeply inclined fault zone, with the block of land on one side being pushed up relative to the downthrown block on the other side
	•	Reverse faults: produced from compression stresses with the upthrown block rising steeply above the downthrown block, so that the fault scarp would be severely over steepened if erosion did not act to smooth the slope somewhat
	•	Thrust faults: compression forces the upthrown block to override the downthrown block at a relatively low angle
	•	Strike-slip faults: the movement is horizontal; a consequence of shear stresses

Landforms Associated with Normal Faulting
Tilted Fault-Block Mountains- when the block is tilted asymmetrically, producing a steep slope along the fault scarp and a relatively gentle slope on the other side of the block

Horst and Graben
Horst- an uplift of a block of land between two parallel faults; a block elevated above the surrounding land

Graben- a block of land bounded by parallel faults in which the block has been downthrown, producing a distinctive structural valley with a straight, steep-sided fault scarp on either side

Landforms Associated with Strike-Slip Faulting
Linear fault trough- the surface trace of a large strike-slip fault may be marked by

Sags- small depressions that develop through the settling of rock within the fault zone


Earthquakes
Earthquake- a vibration in the Earth produced by shock waves resulting from a sudden displacement along a fault

Epicenter- focus of the earthquake where the strongest shocks and greatest crustal vibrations are often felt

Magnitude- describes the relative amount of energy release during an earthquake

Shaking Intensity- directly influences the amount of damage that results from an earthquake


Chapter 15 Preliminaries to Erosion: Weathering and Mass Wasting

Denudation- a term that implies a lowering of continental surfaces
	•	Weathering: the breaking down of rock into smaller components by atmospheric and biotic agencies
	•	Mass wasting: involves the relatively short-distance downslope movement of broken rock material due to gravity
	•	Erosion: consists of more extensive and generally more distant removal, transportation, and eventual deposition of fragmented rock material

Weathering and Rock Openings
	•	Microscopic openings: can be responsible for extensive weathering, may consist of spaces between crystals of igneous or metamorphic rocks, pores between grains of sedimentary rocks, or minute fractures within or alongside mineral grains in any kind of rock
	•	Joints: cracks that develop as a result of stress
	•	Faults: breaks in bedrock along which there is relative displacement of the walls making up the crack
	•	Lava vesicles: holes of various sizes, usually small, that develop in cooling lava when gas is unable to escape as the lava solidifies
	•	Solution cavities: holes formed in calcareous rocks as the soluble minerals are dissolved and carried away by percolating water

The Importance of Jointing
Master joints- where large joints or joint sets extend for long distances and through a considerable thickness of rocks

Mechanical Weathering- the physical disintegration of rock material without any change in its chemical composition

Frost Wedging- the freeze thaw action of water

Salt Wedging- happens when salts crystallize out of solution as water evaporates

Exfoliation- curved layers peel off bedrock

Chemical Weathering- the decomposition of rock by the chemical alteration of its minerals

Oxidation- the oxygen atoms combine with atoms of various metallic elements making up the minerals in the rock and form new products

Hydrolysis- the chemical union of water with another substance to produce a new compound that is nearly always softer and weaker than the original

Carbonation- the reaction between the carbon dioxide in water and carbonate rocks such as limestone to produce a very soluble product that can readily be removed by runoff or percolation and can also be deposited in crystalline form if the water is evaporated

Biological Weathering- when plants and animals contribute to weathering

Mass Wasting
Angle of repose- the steepest angle that can be assumed by loose fragments on a slope without downslope movement

Fall- the falling pieces of rock downslope

Talus/scree- pieces of unsorted, angular rock that fall in a certain fashion

Talus cones- cone-shaped heaps

Rock glaciers- extremely slow flows of talus

Slide
Landslide- an instantaneous collapse of a slope and does not necessarily involve the lubricating effects of water or clay
	•	the sliding material represents a rigid mass that is suddenly displaced without any fluid flow

Slump- slumping involves slope failure in which the rock or regolith moves downward and at the same time rotates outward along a curved slide plane that has its concave side facing upward

Flow
Earthflow- the most common flow movement; a portion of a water-saturated slope moves a limited distance downhill, normally during or immediately after a heavy rain

Mudflow- originates in drainage basins in arid and semiarid country when a heavy rain following a long dry spell produces a cascading runoff too voluminous to be absorbed into the soil

Debris flow- large pieces that occur during mudflow

Creep
Soil creep- consists of a very gradual downhill movement of soil and regolith so unobtrusive that it can normally be recognized only by indirect evidence

Solifluction- a special form of creep that produces a distinctive surface appearance
	•	largely restricted to tundra landscape


Chapter 16 The Fluvial Processes

Streams and Stream Systems
Fluvial processes- those that involve running water

Overland flow- the unchanneled downslope movement of surface water

Streamflow- the channeled movement of water along a valley bottom

Valley- that portion of the terrain in which a drainage system is clearly established
	•	valley bottom: the lower, flatter area that is partially or totally occupied by the channel of a stream, as well as the valley sides

Interfluve- the higher land above the valley sides that separates adjacent valleys

Drainage basins- all the area that contributes overland flow and groundwater to that stream

Drainage divide- the line of separation between runoff that descends in the direction of the drainage basin in question and runoff that goes toward an adjacent basin

Stream Order
First-order stream- the smallest unit in the system; one without tributaries

Second-order stream- when two first-order streams unite

Third-order stream- confluence of two second-order streas

Fluvial Erosion and Deposition
Erosion by overland flow- the collision of raindrops with the gound is strong enough to blast fine soil particles upward and outward, shifting them a few millimeters laterally
Erosion by streamflow- accomplished in part by the direct hydraulic power of the moving water, which can excavate and transport material at the bottom and sides of the stream

Transportation- any water moving downslope can transport rock material

Stream load
	•	dissolved load: when minerals, mostly salts, are dissolved in the water and carried in solution
	•	suspended load: very fine particles of clay and silt that are carried in suspension, moving along water without ever touching the streambed
	•	bedload: sand, gravel, and larger rock fragments

Competence- a measure of the particle size a stream can transport, expressed by the diameter of the largest particles that can be moved

Capacity- a measure of the amount of solid material a stream has the potential to transport, normally expressed as the volume of material passing a given point in the stream channel during a given time interval

Alluvium- the term for stream-deposited debris
	•	characterized by a sorting of particles on the basis of size

The Role of Floods
Discharge- volume of flow

Perennial streams- permanent

Ephemeral streams- impermanent flows

Intermittent streams- flow for only part of the year

Channel Flow
Turbulence- when the general downstream movement is interrupted by irregularities in the direction and speed of the water

Stream Channel Patterns
Straight channels- short and uncommon and usually indicative of strong control by the underlying geologic structure

Sinuous channels- much more common than straight ones; winding channels and are found in almost every type of topographic setting

Meandering channels- exhibit an extraordinarily intricate pattern of smooth curves in which the stream follows a serpentine course, twisting and contorting and turning back on itself…
	•	generally occurs when the land is flat and the gradient is low, and in a stream that has an unhurried flow but is moving with enough force to erode its banks and carry sediment

Braided streams- consist of a multiplicity of interwoven and interconnected channels separated by low bars or islands of sand, gravel, and other loose debris
	•	takes place when a very flat stream channel has a heavy load of alluvium and a period of low discharge

Structural Relationships
Consequent streams- the first to develop on newly uplifted land; many remain consequent throughout their evolutionary development

Subsequent streams- develop along zones of structural weakness; may excavate their channels along an outcrop of weak bedrock, or perhaps follow a fault zone or a master joint

Antecedent streams- the existence of the uplift as the stream antedates

Superimposed streams- originally established on a higher sequence of land that has been entirely or largely eroded away, so that the original drainage pattern becomes incised into an underlying sequence of rocks of quite different structure

Stream drainage patterns
Dendritic drainage pattern- most common; treelike, branching; consists of a random merging of streams, with tributaries joining larger streams irregularly but always at an angle smaller than 90 degrees

Trellis drainage pattern- develops as a response to an underlying structure consisting of alternating bands of tilted hard and soft strata, with long, parallel streams linked by short, right-angled segments

Radial drainage pattern- usually found when streams descend from some sort of concentric uplift, such as an isolated volcano

Centripetal drainage pattern- usually associated with streams converging in a basin

Annular drainage pattern- can develop either on a dome or in a basin where dissection has exposed alternating concentric bands of tilted hard and soft rock

Valley Deepening
Downcutting- lowering of the streambed that involves the hydraulic power of the moving water, the prying and lifting capabilities of turbulent flow, and the abrasive effect of the stream’s bedload as it rolls, slides, and bounces along the channel

Base level- limit to how much downcutting a stream can do

Knickpoints- irregularities in the channel

Knickpoint migration- illustrates dramatically the manner in which valley shape often develops first in the lower reaches and then proceeds progressively upstream, even though the water obviously flows downstream

Valley Widening
Lateral erosion- the main flow of the current swings from one bank to the other, eroding where the water speed is greatest and depositing where it is least
	•	the water moves fastest on the outside of curves and there it undercuts the bank

Valley Lengthening
Headward erosion- erosion that cuts into the interfluve at the upper end of a gully or valley

Stream capture- an event where a portion of the flow of one stream is diverted into that of another by natural processes

Elbow of capture- sharp bend in river course that develops where one stream captures another stream

Delta formation- a landform at the mouth of a river produced by the sudden dissipation of a stream’s velocity and the resulting deposition of the stream’s load

Deposition in Valleys
Aggradation- a process in which alluvium may accumulate on the streambed to such an extent that the bed’s elevation is raised

Floodplains- most prominent depositional landscape; a low-lying, nearly flat alluvial valley floor hat is periodically inundated with flood waters

Floodplain Landforms
Bluff- a relatively steep slope at the outer edge of a floodplain

Cutoff meander- a sweeping stream channel curve that is isolated from streamflow because the narrow meander neck has been cut thorough by stream erosion

Oxbow lake- a cutoff meander that initially holds water

Meander scar- a former stream meander through which the stream no longer flows

Natural levee- an embankment of slightly higher ground fringing a stream channel in a floodplain; formed by deposition during floodtime

Bird’s-foot delta- a series of narrow, sediment-lined distributary channels

Stream Rejuvenation- when a stream gains downcutting ability, usually through regional tectonic uplift

Stream terrace- remnant of a previous valley floodplain of a rejuvenated stream

Entrenched meanders- formed when an area containing a meandering stream is uplifted slowly and the stream incises downward while still retaining the meandering course

Davis’ Geomorphic Cycle
Youth- streams become established and a drainage pattern beings to take shape

Maturity- the main streams approach an equilibrium condition, having worn away the falls and rapids and developed smooth profiles

Old age- erosion reduces the entire landscape to near base level

Rejuvenation- regional uplift could raise the land and interrupt the cycle at any stage

Theory of crystal change and slope development

Equilibrium theory- slope forms are adjusted to geomorphic processes so that there is a balance of energy


Chapter 17 Solution Processes and Karst Topography

Dissolution- an important weathering-erosion process for all rocks, but it is particularly effective on carbonate sedimentary rocks, especially limestone

Caverns and Related Features
Caverns- large opening or cave, especially in limestone; often decorated with speleothems

Speleothem- a feature formed by precipitated deposits of minerals on the wall, floor, or roof of a cave

Stalactite- a pendant structure that grows slowly downward like an icicle from the roof

Stalagmite- a companion feature that grows upward where the drip hits the floor


Karst Topography


Karst- topography developed as a consequence of subsurface solution

Sinkholes- the most common surface feature of karst landscape; rounded depressions formed by the dissolution of surface carbonate rocks, typically at joint intersections

Collapse doline- a sinkhole that results from the collapse of the roof of a subsurface cavern; may have vertical walls or even overhanging cliffs

Tower karst- residual karst features in the form of very steep-sided hills; vertical sides and conical or hemispheric shapes

Disappearing stream- stream that abruptly disappears from the surface where it flows into an underground cavity

Swallow hole- the distinct opening at the bottom of some sinks through which surface drainage can pour directly into an underground channel

Hydrothermal Features
Hydrothermal activity- the outpouring or ejection of hot water, often accompanied by steam, which usually takes the form of either a hot spring or a geyser

Hot spring- hot water at Earth’s surface that has been forced upward through fissures or cracks by the pressures that develop when underground water has come in contact with heated rocks or magma beneath the surface

Geyser- a specialized form of intermittent hot spring with water issuing only sporadically as a temporary ejection, in which hot water and steam are spouted upward for some distance

Fumarole- a hydrothermal feature consisting of a surface crack that is directly connected with a deep-seated source of heat. The little water that drains into this tube is instantly converted to steam by beat and gases, and a cloud of steam is then expelled from the opening


Chapter 18 The Topography of Arid Lands

Special Conditions in Deserts
Weathering- dominant in dry lands; results in generally slower rate of total weathering in deserts, but also in the production of more angular particles of weathered rock

Soil and regolith- thin or absent in most places; a condition that exposes the bedrock to erosion and contributes to the stark, rugged, rocky terrain

Soil creep- smoothing phenomenon in more humid climates

Impermeable surfaces- permitting little moisture to seep into the ground; leads to high runoff when it rains

Sand- allows water to infiltrate the ground and inhibits drainage via streams and overland flow; sand is readily moved by heavy rains; it can be shifted and shaped by the wind

Rainfall- intense, often coming from convective thunderstorms, which means runoff is usually rapid; fluvial erosion and deposition are remarkably effective and conspicuous

Fluvial deposition- depositional features of alluvium are unusually common in desert areas

Wind- high winds are a characteristic of most deserts

Basins of interior drainage- do not drain ultimately into any ocean

Vegetation- the plant cover consists mostly of widely spaced shrubs or sparse grass, which provide little protection from the force of raindrops and function inadequately to bind the surface material with roots

Running Water in Waterless Regions
Exotic streams- a stream that flows into a dry region, bringing its water from somewhere else

Ephemeral streams- a stream that carries water only during the “wet season” or during and immediately after rains

Playa- dry lake bed in a basin of interior drainage

Salina- dry lake bed that contains an unusually heavy concentration of salt in the lake-bed sediment

Saline lake- salt lake; commonly caused by interior stream drainage in an arid environment

Differential erosion- the process whereby different rocks or parts of the same rock erode at different rates

Inselberg- isolated summit rising abruptly from a low-relief surface

Bornhardt- a rounded or domal inselberg composed of very resistant rock that stands above the surrounding terrain because of differential erosion and weathering

Pediment- a gently inclined bedrock platform that extends outward from a mountain front, usually in an arid region

Piedmont- any zone at the foot of a mountain range

Characteristic Desert Surfaces- Ergs, Regs, and Hamadas
Erg- most notable desert surface; the classic “sea of sand” often associated in the public mind with the term desert; a large area covered with loose sand generally arranged in some sort of dune formation by the wind

Reg- a tight covering of coarse gravel, pebbles, and/or boulders from which all sand and dust have been removed by wind and water

Desert pavement- hard and relatively impermeable desert surface of tightly packed small rocks

Desert varnish- dark, shiny coating, consisting mostly of iron and manganese oxides, that forms on the surface of pebbles, stones, and larger outcrops after long exposure to the desert air; characterized by a high content of iron and manganese oxides along with wind-delivered clay

Hamada- barren surface of consolidated material

The Work of the Wind
Aeolian processes- processes related to wind action that are most pronounced, widespread, and effective in dry lands

Deflation- the shifting of loose particles as a result of their being blown either through the air or along the ground

Blowout- a shallow depression from which an abundance of fine material has been deflated

Abrasion- analogous to fluvial abrasion, except much less effective

Sand dune- lose, windblown sand heaped into a mound or low hill

Slip face- steeper leeward side; typically maintains an angle of 32 degrees to 34 degrees

Barchan- usually occurs as an individual dune migrating across a nonsandy surface; crescent-shaped, with horns of the crescent pointing downwind
Transverse dunes- also crescent-shaped but less uniformly so than barchans; occur wehre the supply of sand is much greater than that found in locations that have barchans; sand covered

Siefs- long, narrow dunes that usually occur in multiplicity and in a generally parallel arrangement

Loess- a form of Aeolian deposit not associated with dry lands; wind-deposited silt that is fine grained, calcareous, and usually buff colored

Two Characteristic Desert Landform Assemblages
Alluvial fan- a fan-shaped deposition feature laid down by a stream issuing from a mountain canyon

Bajada- a continual alluvia surface that extends across the piedmont zone, slanting from the range toward the basin, in which it is difficult to distinguish between individual fans

Sapping- groundwater seeps and trickles out of the scarp face, eroding fine particles and weakening the cohesion of the face

Scarp- pertains to steep, more or less vertical cliffs

Butte- an erosional remnant having a very small surface area and cliffs that rise conspicuously above their surroundings

Pinnacle- a final spire of resistant caprock protecting weaker underlying beds

Badlands- intricately rilled and barren terrain of arid and semiarid regions, characterized by a multiplicity of short, steep slopes


Chapter 19 Glacial Modification of Terrain

Types of Glaciers
Continental ice sheets- glaciers that formed in nonmountainous areas of the continents

Highland ice field- largely unconfined ice sheet in high mountain area

Valley glacier- a long, narrow feature resembling a river of ice, which spills out of its originating basins and flows down-valley

Cirque glaciers- very small alpine glaciers confined to the basins where they originate

Glacier Formation and Movement
Accumulation- addition of ice by incorporation of snow

Ablation- wastage of ice through melting and sublimation

Firn- snow granules that have become packed and begin to coalesce due to compression, achieving a density about half as great as that of water

Accumulation zone- the upper portion of a glacier where there is a greater annual accumulation of ice than there is wastage

Ablation zone- the lower portion of a glacier where there is a net annual loss of ice due to melting and sublimation

Equilibrium line- accumulation exactly balances ablation

Basal slip- the term used to describe the sliding of the entire mass at the bottom of a glacier over its bed on a lubricating film of water

The Effects of Glaciers
Glacial plucking- action in which rock particles beneath the ice are grasped by the freezing of meltwater in joints and fractures and pried out and dragged along in the general flow of a glacier. Also called glacial quarrying

Glacial abrasion- the bedrock is worn down by the rock debris being dragged along in the moving ice

Glacial flour- rock material that has been ground very fine

Drift- the general term for all material moved by glaciers

Till- rock debris deposited directly by moving or melting ice, with no meltwater flow or redeposition involved

Glacial erratics- outsize boulder included in the glacial till, which may be very different from the local bedrock

Glaciofluvial deposition- the action whereby much of the debris that is carried along by glaciers is eventually deposited or redeposited by glacial meltwater

Continental Ice Sheets
Roche moutonnee- often produced when a bedrock hill is overridden by moving ice

Till plain- an irregularly undulating surface of broad, low rises and shallow depressions produced by the uneven deposition of glacial till

Moraine- a general term for glacier-deposited landforms composed entirely or largely of till

Terminal moraine- a ridge of till that marks the outermost limit of glacial advance

Recessional moraine- ridges that mark positions where the ice front was temporarily stabilized during the final retreat of the glacier

Ground moraine- formed when large quantities of till are laid down from underneath the glacier rather than from its edge

Kettles- form when large blocks of ice left by a retreating glacier become surrounded or even covered by glacial drift; after the ice block melts, the morainal surface collapses, leaving an irregular depression

Drumlin- a low, elongated hill formed y ice sheet deposition. The long axis is aligned parallel with the direction of ice movements, and the end of the drumlin that faces the direction from which the ice came is somewhat blunt and slightly steeper than the narrower and more gently sloping end that faces in the opposite direction

Stratified drift- there has been some sorting of the debris as it was carried along by the meltwater

Outwash plains- smooth, flat alluvial aprons deposited beyond recessional or terminal moraines by streams issuing from the ice

Esker- long, sinuous ridge of stratified glacial drift composed largely of glaciofluvial gravel and formed by the choking of subglacial streams during a time of glacial stagnation

Kames- small, steep mounds or conical hills of stratified drift are found sporadically in areas of ice-sheet deposition

Mountain Glaciers
Cirque- a broad amphitheater hollowed out at the head of a glacial valley

Arête- a narrow, jagged, serrated spine of rock; remainder of a ridge crest after several glacial cirques have been cut back into an interfluve from opposite sides of a divide

Col- a pass or saddle through a ridge produced when two adjacent glacial cirques on opposite sides of a divide are cut back enough to remove part of the arête between them

Horn- a steep-sided, pyramidal rock pinnacle formed by expansive glacial quarrying of the headwalls where three or more cirques intersect
Glacial trough- a valley reshaped by an alpine glacier, usually u-shaped

Glacial steps- series of level or gently sloping bedrock benches alternating with steep drops in the down-valley profile of a glacial trough

Paternoster lakes- a sequence of small lakes found in the shallow excavated depressions of a glacial trough

Hanging valleys- a tributary glacial trough, the bottom of which is considerably higher than the bottom of the principal trough that it joins

Lateral moraines- well-defined ridges of unsorted debris built up along the sides of valley glaciers

Medial moraine- a dark band of rocky debris down the middle of a glacier created by the union of the lateral moraines of two adjacent glaciers

The Periglacial Environment
Patterned ground- polygonal patterns in the ground that develop in areas of seasonally frozen soil and permafrost


Chapter 20 Coastal Processes and Terrain

Coastal Processes
Swell- a water wave, usually produced by stormy conditions, that can travel enormous distances away from the source of the disturbance

Wave of oscillation- motion of wave in which the individual particles of the medium make a circular orbit as the wave form passes through

Wave height- the vertical distance from wave crest to trough

Wave of translation- the horizontal motion produced when a wave reaches shallow water and finally “breaks” on the shore

Swash- the cascading forward motion of a breaking wave that rushes up the beach

Backwash- water moving seaward after the momentum of the wave swash is overcome by gravity and friction

Wave refraction- phenomenon whereby waves change their directional trend as they approach a shoreline

Tsunami- very long wavelength oceanic wave generated by submarine earthquake, landslide, or volcanic eruption; also called seismic sea wave
Eustatic sea-level change- change in sea level due to an increase or decrease in the amount of water in the world ocean, also known as eustasy

Longshore currents- the water moves roughly parallel to the shoreline; develop just offshore and are set up by the action of the waves striking the coast at a slight angle

Beach drifting- the zigzag movement of beach particles in which the net result is a displacement parallel to the coast in a general downwind direction

Sediment budget- the balance between the sediment being deposited on a beach and the sediment that is being transported away from a beach

Coastal Landforms
Beach- an exposed deposit of loose sediment adjacent to a body of water

Spit- a linear deposit of marine sediment that is attached to the land at one or both ends

Baymouth bar- a spit that has become extended across the mouth of a bay to connect with a headland on the other side, transforming the bay into a lagoon

Tombolo- a localized cyclonic low-pressure cell surrounded by a whirling cylinder of violent wind; characterized by a funnel cloud extending below a cumulonimbus cloud

Barrier island- a long, narrow sandbar built up in shallow offshore waters, sometimes only a few hundred meters from the coast but often several kilometers at sea

Lagoon- a body of quiet salt or brackish water

Jetties- confine the flow of water to a narrow zone, thereby keeping the sand in motion and inhibiting its deposition in the navigation channel

Ria shoreline- a long, narrow inlet of a river that gradually decreases in depth from mouth to head

Fjord- a glacial trough that has been partly drowned by the sea

Wave-cut platform- gently sloping, wave-eroded bedrock platform that develops just below sea level; common where coastal cliff is being worn back by wave action

Marine terrace- a platform of marine erosion that has been uplifted above sea level

Fringing reef- a coral reef built out laterally from the shore, forming a broad bench that is only slightly below sea level, often with the tops of individual coral “heads” exposed to the open air at low tide

Barrier reef- a prominent ridge of coral that roughly parallels the coastline but lies offshore, with a shallow lagoon between the reefs and the coast

Atoll- coral reef in the general shape of a ring or partial ring that encloses a lagoon