OPLDatabaseFile 670-km discontinuityBoundary that separates the upper mantle (35-670 km) from the lower mantle (670-2900 km). It could be a natural barrier to whole-mantle convection. hA-type earthquakeUEvents with clear P-waves and S-waves occurring under volcanoes at depths of 1-10 km.aaHawaiian term used to describe a lava flow whose surface is broken into rough angular fragments. Aa flows commonly develop from pahoehoe flows as they cool and lose gas. ablation (glacial)All processes which include melting evaporation (sublimation) wind erosion and calving (breaking off of ice masses) that remove snow or ice from a glacier or snowfield. The term also refers to the amount of snow orice removed by these processes.
t
absolute dateeAn estimate of the true age of a mineral or rock based on the rate of decay of radioactive minerals. u
abyssal plainfThe broad expanse of sea floor lying between about 3 and 6 kilometers (-2 to 4 miles) below sea level.U
accelerometerFA seismograph for measuring ground acceleration as a function of time.accretionary wedgekAccumulation on the ocean floor of sedimentary material scraped off the subducted plate by the upper plate.Baccumulation (glacial)All processes including snowfall condensation avalanching snow transport by wind and freezing of liquid water that add snow or ice to a glacier floating ice or snow cover. The term also includes the amount of snow or other solid precipitation added to a* glacier or snowfield by these processes.qaccumulative mineralsZMinerals that make up the extract assemblage during fractional crystallization of a magma.t active faultfA fault along which slip has occurred in historical (or Holocene) time or earthquake foci are located.v active lobei of a delta. The site on a delta where functioning distributary channels cause the delta to grow seaward.active volcanoA volcano that is erupting; or one that while not erupting at the present has erupted within geologically recent time and is considered likely to do so in the geologically near future. actualismThe interpretation of ancient rocks by applying the results of analyses of modern-day geologic processes in accordance with the principle of uniformitarianism.^
adaptationRA feature of an organism that serves one or more functions useful to the organism.adaptive breakthroughAn evolutionary innovation that affords a group of organisms a special ecologic opportunity and often leads to the adaptive radiation of that group.adaptive radiationEvolutionary diversification of a taxon's morphology, ecology, physiology, behavior and other characteristics over a geologically short time interval leading to the appearance of a number of new taxa.gadaptive radiationSThe rapid origins of many new species or higher taxa from a single ancestral group.Daeolian deposits2Sedimentary deposits consisting of windblown dust.AFMAGAudio Frequency Magnetic technique in which natural electomagnetic fields in the audio-frequency range are used to study lateral changes in earth resistivity.
aftershockAn earthquake which follows a larger earthquake or main shock and originates in or near the rupture zone of the larger earthquake. Generally, major earthquakes are followed by a larger number of aftershocks decreasing in frequency with time. Dage? geologic. The division of geologic time smaller than an epoch. aggregationThe process of combination of very small volcanic ash or dust particles in volcanic plumes in the atmosphere to form larger particles which settle out rapidly to the earth's surface due to their large diameter.Agung,Active volcano, elevation 3141 m (10380 ft)Y in Bali, Indonesia (8.342 S 115.508 E). Agung is known to have erupted three times, the last in 1964.albedoThe percentage of solar radiation reflected from the earth's surface. This percentage is higher for ice than for land or water and usually higher for land than for water.p algal ridgecThe durable structure formed by coralline algae that buttresses the front of a modern coral reef.malkaneeOne of the group of hydrocarbons of the paraffin series, for example methane, ethane and propane.jallelochemicalsYChemicals produced by one soecies that enter the environment and influence other species.allochthonous clayClay originating in an environment different from the final sedimentary environment (rocky substrate soil or upstream sediment subjected to erosion).alluviumUnconsolidated detrital material deposited during comparatively recent geologic time by a stream or river. Alluvial deposits include mid channel bars, point bars, floodplain deposits,%alluvial fans, and fluvial terraces. alluvlal fanA low cone-shaped structure that forms where an abrupt reduction in slope -- for example, the transition from a highland area to a broad valley -- causes a stream to slow down. amniote eggThe type of egg laid by reptiles and birds having a nutritious yolk and a hard outer shell to protect the embryo from the dry environment. The amniote egg is named for the amnion a sac that contains the embryo.D amplitude9The maximum height of a wave crest or depth of a trough. AMTAudio MagnetoTelluric method in which magnetotelluric measurements are made in the audio frequency range (10-10,000 Hz) for medium to shallow depth investigation.andesite~ A find-grained extrusive igneous rock intermediate in composition between rhyolite which is felsic and basalt which is mafic.andesiteIntermediate volcanic rocks containing 54 to 62 percent silica and moderate amounts of iron and magnesium. Andesite minerals commonly include plagioclase and hornblende with lesser amounts of mica, pyroxene and various accessory minerals. Andesites are aphanitic in texture and are usually medium dark in color. They occur with composite volcanic cones associated with convergent plate margins. |angular unconformityfAn unconformity separating horiiontal strata above from older strata that had been tilted and eroded. f anhydrite[The mineral that consists of calcium sulfate (CaS04) or the rock composed of this mineral.anomaly magnetic. A local increase or decrease in the strength of the earth's magnetic field caused by the magnetism of nearby sediments or rocks.d anticlineYA fold that is concave in a downward direction -- that is the vertex is the lowest point._ aquicludeTAn impermeable geologic formation or stratum which will not hold or transmit fluid. maquiferdSaturated permeable geologic unit that can store and transmit significant quantities of groundwater.UaquitardKA geologic formation or stratum that significantly retards fluid movement.
arc tholeiite|Basalt with a characteristic chemical composition found in an island or continental volcanic arc (also a high-K tholeiite).narraygAn ordered arrangement of seismometers or geophones the data from which feeds into a central receiver. ?arrival6The appearance of seismic energy on a seismic record. O arrival timeAThe time at which a particular wave phase arrives at a detector.
artesian wellA well in an aquifer where the groundwater is confined under pressure and the water level will rise above the top of the confined aquifer. artificial recharge~The unnatural addition of surface waters to groundwater. Recharge could result from reservoirs storage basins, leaky canals,+ direct injection of water into an aquifer,2 or by spreading water over a large land surface. aseismicNot associated with an earthquake as in aseismic slip. Also used to indicate an area with no record of earthquakes; an aseismic zone.
ashFine particles of rock material ejected during an explosive volcanic eruption (commonly intermediate to felsic events). Ash may be either solid or molten when first erupted and generally measures less than 0.10 inch in size (larger particles have other names). ash flowA turbulent mixture of gas and rock fragments most of which are ash-sized particles ejected violently from a crater or fissure. The mass of pyroclastics is normally of very high temperature and moves rapidly down the slopes or even along a level surface. ashfall (subaerial)Volcanic ash that has fallen through the air. The resulting deposit is usually well sorted and exhibits a finely layered structure. _
asthenosphereThe layer below the lithosphere which is marked by low seismic wave velocities and high seismic wave attenuation and probably partially molten. The layer or shell of Earth below the lithosphere which is weak and in which large-scale isostatic adjustmentsP take place, magmas may be generated,and seismic waves are strongly attenuated.RatollKA circular or horseshoe-shaped organic reef growing on a submerged volcano. authigenesisuProcess by which new minerals form in place within a sediment during deposition or in the early stages of diagenesis.autochthonous clayClay originating in the soft sediment or sedimentary rock where it is identified and where it formed either by neoformation (i.e., from dissolved elements) or by transformation (i.e., from mineral growth on preexisting sedimentary substrate).9 avalancheA large mass of material falling or sliding rapidly due to the force of gravity. In many cases, water acts as a catalyst and/or lubricant. Avalanches often are classified by what is moving, such as a snow, ice, soil, or rock avalanche. A mixture of these. materials is commonly called a debris flow. c axial plane+An imaginary plane that cuts through a fold* dividing it as symmetrically as possible.B-type earthquake'Events with weak P-waves and no S-wavesI a low-frequency content and occurring under volcanoes at depths < 1 km.banded iron formationAn iron formation that consists of alternating iron-rich and iron-poor layers. Most rocks of this type are older than about 2 billion years.barrier islanduAn elongate island composed of sand heaped up by waves that lies approximately parallel to the shoreline of an ocean. barrier reefAn elongate organic reef that parallels a coastline and is large enough to dissipate ocean waves, leaving a quiet-water lagoon on its landward side.b
basal slidingSThe movement or speed of movement of a glacier on its bed. Also called basal slip.basaltVolcanic rock (or magma) that is generally dark in color, contains 45 to 54 percent silica, and is rich in iron and magnesium. An eruption of basaltic magma is generally quiet and results in flows (both vesicular and non-vesicular) and breccias. Undersea eruptions commonly result in the formation of "pillow lavas." Basalt represents the initial differentiated material erupted by the earth at spreading centers. basement rocksRocks beneath a large geologic feature (such as the fold-and-thrust belt of a mountain system) which are genetically unrelated to the overlying feature.FbedAA distinct sedimentary layer (stratum) thicker than 1 centimeter.T belemniteIExtinct invertebrate animal (cephalopod) known from cigar-shaped fossils. Benioff zoneA narrow zone defined by earthquake foci and tens of kilometers thick dipping from the surface under the Earth's crust. Zone of earthquake foci produced near the surface of and within the subducted lithosphere.benthic foraminifera0Benthic protozoans (i.e., live on the seafloor)which may form carbonate tests. The tests are preserved in sediments and form an important basis for paleoceanographic reconstructions. bentoniteA clay material composed principally of the mineral montmorillonite. It has a great affinity for fresh water and when hydrated will increase its volume more than seven times. Water/bentoninte suspensions are essentially impermeable. Commonly used as a sealant for ponds. Rbimodal distributionTemperature above which there is no spontaneous magnetization.daciteVolcanic rock (or lava) that characteristically is light in color and contains 62 to 69 percent silica and moderate amounts of sodium and potassium. =debris avalancheA flow of unsorted masses of rock and other material downslope under the influence of gravity. Water is commonly involved as a catalyst and/or lubricant. For example, a rapid mass movement that included fragmented cold and hot volcanic rock, water, snowc, glacial ice, trees and other debris and hot pyroclastic material was associated with the May 181980 eruption of Mt. St. Helens. Most of the deposits in the upper valley of the North Fork Toutle River and in the vicinity of Spirit Lake are from the debris avalanche resulting from the eruption. Ldendritic crystals8Crystals that grow in a branching form resembling trees.dendrogeomorphologyApplication of tree-ring studies (dendrochronology) to the interpretation of geomorphologic processes. Often supplemented by related botanical observations.cdensity'The mass per unit volume of a substance2 commonly expressed in grams per cubic centimeter.^detachment planeLThe surface along which a landslide disconnects from its original position. detritus{Loose rock or mineral material that is dislodged from bedrock by mechanical means and transported from its place of origin. dew pointThe temperature (elevation) where adiabatic cooling results in the initiation of condensation of water vapor into cloud droplets. di-polarThe arrangement of the hydrogen atoms of a water molecule at 105 deg. across the oxygen results in a slight electrical charge to the molecule.
diagenesisChemical and physical changes undergone by a sediment after its initial deposition, exclusive of surficial alteration (chemical weathering) and metamorphism (pervasive recrystallization). Includes processes like compaction, cementation and replacement.` differentiation (fractionation)Process by which one magma gives rise to another of different composition. Differentiated or fractionated magmas are said to be evolved from a more primitive parent. Processes by which magmas evolve from basaltic to more silicic compositions; includes cry?stal fractionation, magma mixing, and crustal contamination.!diffusion of magnetic field linesMotion of magnetic field lines through an electrically conducting fluid by virtue of the fluid's finite electrical resistivity.k dilatancy`Inelastic volume increase caused by the occurrence of small cracks in rock or soil under stress.dipThe angle by which a rock layer or fault plane deviates from the horizontal. The angle is measured in a plane perpendicular to the strike.dip-slip faultA fault in which the relative displacement is along the direction of dip of the fault plane; the offset is either normal or reverse.discharge areaRegion in which there is a net loss of water from the groundwater system (discharge) to surface water bodies or by evapotranspiration.ldispersion (wave)YThe spreading out of a wave train due to each wavelength traveling with its own velocity. displacementVector defining offset on a fault that may represent slip in a single event or the accumulation of slip over a much longer time.wdissolved loadVPart of the total stream load consisting of substances in dissolved form such as Ca2+, HCO-3, H4SiO4.domeA steep-sided mass of viscous (doughy) lava extruded from a volcanic vent often circular in plane view and spiny, rounded, or flat on top. Its surface is often rough and blocky as a result of fragmentation of the cooler, outer crust during growth of the dome. dormant volcanoA volcano that is presently inactive but which may erupt again. The major volcanic cones of the Cascade Range in Washington, Oregon, and California, for example, are believed to be dormant rather than extinct. Cdrift (glacial)2General term for material deposited by a glacier. duricrustIndurated soil crust or hardcap occurring on or near an eroded planation surface. May be indicative of climatic change from tropical to drier conditions with alternating wet and dry seasons. Contains tubular voids acting as avenues of translocation.dust veil indexA quantitative method developed by H. H. Lamb for comparing the magnitude of volcanic eruptions. The formulae use observations either of the depletion of the solar beam, temperature lowering in the middle latitudes, or the quantity of solid matter dispersed as dust. The reference dust veil index is 1000, assigned to the Krakatoa 1883 eruption and the index is calculated using all three methods, where the information is available for statistical comparison purposes. Abbreviated D.V.I.
dynamo actionProcess whereby motions within an electrcally conducting fluid, interacting with a magnetic field, convert their kinetic energy into magnetic energy, thereby sustaining the magnetic field.{
earthquakeoThe vibration of the Earth caused by the passage of seismic waves radiating from some source of elastic energy.earthquake swarm xA series of minor earthquakes, none of which may be identified as the main shock, occurring in a limited area and time. eccentricity0Measures how elliptical the earth-sun orbit is, Zwith consequent effects on solar radiation received by the earth. If e is the eccentricityR then (1 + e)/(1 - e) is the ratio of the farthest and closest earth-sun distance.ecosystem function0Ecological processes such as primary production, decomposition, and nutrient cycling that occur at the scale of a system and are affected by a variety of organisms and the environment's microclimate. effective diffusion coefficientMeasure of the rate of diffusion of a substance in a heterogeneous medium like a sediment-water system. Tortuosity resulting from the presence of solid particles is accounted for in this type of coefficient.ejectaXMaterial that is thrown out by a volcano, including pyroclastic material (tephra) and, # from some volcanoes. lava bombs. Fejecta blanket6Circular apron of debris surrounding an impact crater.
El Chichon%Active volcano in Mexico (17.360 N, p93.228 W), elevation 2225 m (7300 ft). El Chichon is known to have erupted five times, most recently in 1983.elastic rebound theoryThe theory of earthquake generation proposing that faults remain locked while strain energy slowly accumulates in the surrounding rock*and then suddenly slip, releasing energy. elastic waveA wave that is propagated by some kind of elastic deformation, that is, a change in shape that disappears when the forces are removed. A seismic wave is a type of elastic wave. selectronegativity`Relative measure (on a scale of 4) of an atom's attraction for the electrons in its outer shell.~enrichment factorkRatio of chemical concentration of an element in a weathered material to that in its fresh parent material.f epicenter[The point on the Earth's surface directly above the focus (or hypocenter) of an earthquake.lequilibrium lineZThe level on a glacier where accumulation equals ablation and the net balance equals zero.eruption columnA mixture of hot volcanic ash, gases and entrained atmospheric air that rises vertically above an erupting volcano to heights of several tens of kilometers in the earth's atmosphere. The rise of the column is in part due to kinetic energy of the jet of gases and ash issuing from the volcano, but primarily due to the buoyant rise of the low-density mixture in the cooler atmosphere.eruption plumeDispersla of an eruption column downwind from the volcano, due to the effects of prevailing atmospheric circulation in the atratosphere and troposphere.
Euler polePole passing through the center of the earth about which a plate can rotate as a rigid body from any initial to any final position on the earth's surface. kevapotranspirationWWater used by plants and animals and subsequently returned directly to the atmosphere. o evergreendConiferous, needle-leaved or sclerophyllous plant that does not echibit a marked seasonal leaf fall.1exogenic cyclePortion of the earth's system involved in the movement and mass transfer of substances through the cycle of weatherin, erosion,#transportation, deposition, burial,Vdiagenesis and uplift. Reservoirs in the cycle generally include the atmosphere, ocean% biota, sediments and shallow crust.exogenic systemYEarth's interacting envelopes: the hydrosphere (mostly the ocean), atmosphere, biosphere,reactive lithosphere (that part of the rocky crust within reach of the processes of weathering). The processes of deep seawater circulation at spreading ridges overlap with endogenic (within the earth) processes. Also relevant are extraterrestrial process{es. Refractory problems such as mass extinction usually become arenas for competing theories drawn from the three sources.explosion earthquakeEvents with ground waves (including P-waves and S-waves) and often air waves, which travel through the air and are transmitted back into the ground in the vicinity of the seismometer.yextinct volcanohA volcano that is not presently erupting and is not likely to do so for a very long time in the future. extract assemblageAssemblage of accumulative minerals extracted from a parent magma duting fractional crystallization to produce a daughter magma.fallout-Settling and deposition of particulate matter] such as tephra and volcanic aerosols out of an eruption plume and onto the earth's surface.EfaultA fracture or zone of fractures in rock along which the two sides have been displaced relative to each other parallel to the fracture. The total fault offset may range from centimeters to kilometers. Large fracture in the ground with two sides displaced r>elative to each other in drections parallel to the fracture. X fault planeKThe plane that most closely coincides with the rupture surface of a fault. ^FEMYFrequency Electromagnetic Method, in which the primary field is sinusoidal in character. ferro-magnesian elementsElements that are readily substituted into silicate minerals that have Fe and Mg as major constituents. Examples include Cr, Ni, V, Sc, Co.firnMaterial that is transitional between snow and glacier ice. It is formed from snow after passing through one summer melt season and becomes glacier ice after its permeability to liquid water falls to zero. fissuresElongated fractures or cracks on the slopes of a volcano. Fissure eruptions typically produce liquid flows,but pyroclastics may also be ejected. flood basaltLaterally extensive deposits of basaltic lava flows resulting from outpouring of vast volumes of magmas during fissure eruptions.
flow rheologyDeformational character of the flow when stress is applied. Rheology varies due to differences in fluid strength, viscosity, density and sediment concentration.fluid inclusionBubble of liquid or gas trapped inside a solid mineral-phase, usually formed during crystallization of the mineral in the presence of a fluid phase. Tiny cavities, 1.0-100 microns in diameter, containing liquid and/or gas,formed by the entrapment of fluid in crystal irregularities. Fluid inclusions provide information on the temperature, pressure,]and chemical composition of the fluids and/or gases trapped at the time of mineral formation. fluorescence&Emission of a certain wavelength lightY resulting from and occurring only during the absorption of light of another wavelength. z
foreshocksnSmaller earthquakes preceding the largest earthquake of a series concentrated in a restricted crustal volume. fumaroleA vent or opening through which issue steam, hydrogen sulfide or other gases. The craters of many dormant volcanoes contain active fumaroles. fumarolic emissionXLow-level and generally steady output of low-temperature gases such as sulfur, halogens,`water vapor and carbon dioxide from dormant volcanoes and geothermal fields in volcanic regions.,galvanic interactionRedox reaction between two mineral entities with different rest potential, where the mineral with lower rest potential acts as reductant and the mineral with the higher rest potential acts as oxidant/reductant in conveying electrons to oxygen or some other suitable acceptor. Ygas-to-particle reaction?The formation of particles by the rapid condensation of a gas. zGaussian coefficientscCoefficients of a spherical harmonic expansion of the potential function of the geomagnetic field. NgeodeticDPertaining to measurement of the shape and dimensions of the earth. f
geodimeterZA surveying instrument to measure the distance between two points on the Earth's surface. geoidLevel (or equipotential) surface at mean sea level. Surface of constant gravitational potential that is chosen to define the earth's shape. At sea the geoid corresponds to the time-averaged surface of the ocean (to an accuracy of 1-2 m). \geomagnetic fieldIMain magnetic field of the earth -- the part generated within the earth. geomagnetic polarity time scaleReference for the polarity history of the geomagnetic field, including current correlations of polarity intervals to biozonations, geologic stages and numerical ages. O
geomorphologybThe study of present-day landforms, including their classification, description, nature, origin development, and relationships to underlying structures. Also the history of geologic changes as recorded by these surface features. The term is sometimes restricted to features produced only by erosion and deposition. geophysical noiseFluctuations in a geophysical parameter that are of a quasirandom nature and cannot be attributed to fluctuations in known causative phenomena. geopotential modelsSet of coefficients of a series representation of the earth's gravitational field in terms of spherical harmonics. geopressured systemsHydrothermal systems contained in sedimentary rock in regions of normal geothermal gradient. They represent a special case in which the pore fluids are under pressure exceeding the hydrostatic pressure. Igeothermal power7Power generated by using the heat energy of the earth. glacial abrasionA common mechanical weathering process where rock and debris frozen into the sides and bottom of a glacier act like sandpaper and wear down the bedrock the glacier is mowing across. glacial maximum~The position or time of the greatest advance of a glacier (e.g., the greatest equatorward advance of Pleistocene glaciation). glacial reboundThe isostatic adjustment of previously glaciated areas after glacial retreat (e.g., the uplift of Scandinavia after the most recent glaciation. glacierA mass of land ice that is formed by the cumulative recrystallization of firn. A glacier flows slowly from an accumulation area to an ablation area. Some well-known glaciers are: the Zermatt, Stechelberg, Grinelwald, and Les Diablerets in Switzerland; the Nigards, Gaupne,' Fanarak, and Lom in Norway; the Wright Taylor and Wilson Piedmont glaciers in Antarctica; Grinnell glacier in Glacier National Park, Montana, U.S., and the Teton glacier in Teton National Park, Wyoming, U.S. glaclolacustrineUsed to describe sediments deposited in a lake in contact with or receiving most of its water and sediments from a glacier, and also landforms resulting from such deposition. grabenA relatively depressed crustal unit bounded by faults on its long sides. Grabens may range in scale from meters to many kilometers. Rift valley becomes the preferred term when dimensions approach the thickness of the brittle crust (>30 km).Ygreat earthquakeGAn earthquake having a magnitude of 8 or greater on the Richter scale. greenhouse or icehouseUseful polarized concepts of the state of the planet. "Greenhouse" collects together global warmth, flattened thermal gradients, increased humidity, high sea level and reduced vigor of oceanic circulation with a tendency toward enhanced anoxia in some parts of the ocean. "Icehouse" is essentially the reverse state in that assemblage of generalizations. It is important to add not-so-icecap-prone and icecap-prone, respectively, without implying necessarily that the world was ever ice-free. grenzA soil horizo, frequently marked by a bed of clay that results from a temporary halt in the accumulation of vegetal material. groundwater~The supply of fresh water found beneath the surface of the Earth (usually in aquifers) that often supplies wells and springs. harmonic tremorA continuous release of seismic energy typically associated with the underground movement of magma. It contrasts distinctly with the sudden release and rapid decrease of seismic energy associated with the more common type of earthquake caused by slippage }along a fault. The seismic signal is characterized by a nearly monotonic sinusoidal appearance and low frequency (0.5-5 Hz).L heat sinkAThat portion of a thermodynamic system that absorbs unused heat. <hertz5The unit of frequency equal to one cycle per second. )historical biogeographyDiscipline that deals with the ever-changing distribution of organisms, marine and non-marine, over the earth's surface through geologic time; i.e., the historical counterpart of present-day biogeography, which discusses the modern distribution of all living organisms. hHolocene.The most recent epoch of the Quaternary period/ covering approximately the last 10,000 years. Y
homopycnalMDescribes water entering a lake that has the same density as the lake water. yhotspotpName commonly given to the surface expression (uplift, volcanism, high-heat flow) of an upwelling mantle plume. humic acidsSuite of organic acids (RCOOH) of indefinite composition and molecular structure produced by decomposition and condensation reactions. Operationally defined as being solubilized from peat, humus, soil, sediment or other material by dilute-alkali extraction. hydrosphereThe aqueous envelope of the Earth, including the oceans, freshwater lakes, rivers, saline lakes and inland seas, soil moisture and vadose water, groundwaters and atmospheric vapor. hydrothermal activityInteraction of an aqueous solution with rock at high temperature and pressure, leading to alteration of the rock and dissolution of some of the rock minerals and formation of others. R hyperpycnalEDescribes water that is denser than the water in the lake it enters. C
hypocenter7The calculated location of the focus of an earthquake. ice ageA glacial epoch or time of extensive glacial activity. Also, as Ice Age, which refers to the latest glacial epoch, the Pleistocene Epoch. Periods characterized by very low temperature worldwide and advancing glaciers. ice coreDeep drill into the earth's permanent glaciers revealing the history of the atmospheric gas and dust content, enabling deduction of former atmospheric temperatures. ice sheetA glacier of considerable thickness and more than 50,000 sq. km in area. It forms a continuous cover of ice and snow over a land surface. An ice sheet is not confined by the underlying topography but spreads outward in all directions. During the Pleistoce ne Epoch ice sheets covered large parts of North America and northern Europe but they are now confined to polar regions (e.g., Greenland and Antarctica). Also called continental glacier. I ice shelfA sheet of very thick ice with a level or gently undulating surface. It is attached to the land on one side, but most of it is floating. On the seaward side it is bounded by a steep cliff (ice front) two to 50 m or more above sea level. Ice shelves have formed along polar coasts (e.g., Antarctica and Greenland); they are very wide, with some extending several hundreds of kilometers toward the sea from the coastline. They increase in size from annual snow accumulation and seaward extension of land glacier's. They decrease in size from warming, melting and calving.
ice streamsLarge, fast glaciers embedded in slow-moving ice. Flow velocities are a few hundred meters to kilometers per year. icebergA floating ice mass up to 100 km long and 200-300 m thick that has broken off (calved) from ice shelves, glaciers or coastal ice cliffs into the ocean.
impact craterwCircular, rimmed depression produced by the impact of a solid body traveling at more than a few kilometers per second. 3 impedanceApparent resistance to flow of alternating current; it is analagous to electrical resistance in direct current method and is a complex quantity. For plane wave electromagnetic sources. the impedance of the ground is equal to the ratio of the orthogonal ho(rizontal electric and magnetic fields. inductionProcess by which a body becomes magnetized or electrified by merely placing it in a magnetic or electric field. Also refers to the process under which electric currents are initiated in a conductor by merely placing it in an electromagnetic field. pinfrared radiationElectromagnetic radiation lying in the wavelength interval from 0.7 microns to 1000 microns. Its lower limit is bounded by visible radiation and its upper limit is bounded by microwave radiation. Most of the energy emitted by the Earth and its atmosphere is at infrared wavelengths. Infrared radiation is generated almost entirely by large-scale intramolecular processes. The tri-atomic gases, such as water vapor, carbon dioxide, and ozone absorb infrared radiation and play important roles in the propagatio\n of infrared radiation in the atmosphere. Abbreviated IR; also called longwave radiation. T integrated time scale (Eocene)The Eocene rock record initially was and still is recognized by its characteristic fossils; fossils are cross-checked against the geomagnetic reversal scale. But rates of change and other quantifications demand numerical calibration -- time in millions of years -- which is founded ultimately in isotopic decay in the potassium-argon and other decay series. The geomagnetic scale consists of chrons, of which Chron C24 and Chron C19 are important here. Some fossil successions have their own names; thus, e.g.4, the Wasatchian North American "land mammal age."8 intensityA measure of the effects of an earthquake at a particular place on humans, structures and (or) the land itself. The intensity at a point depends not only upon the strength of the earthquake (magnitude) but also upon the distance from the earthquake to the- point and the local geology at that point. 6ion1An atom or molecule that has an electric charge. isoseismal lineA line connecting points on the Earth's surface at which earthquake intensity is the same. It is usually a closed curve around the epicenter. isostasyThe vertical readjustment of the surface of the earth due to the addition or removal of weight. Commonly associated with the advance and retreat of glacial ice.
isostatic adjustmentThe process whereby lateral transport at the Earth's surface from erosion or deposition is compensated for by movements in a subcrustal layer to maintain equilibrium among units of varying masses and densities. Also called isostatic compensation. WisothermMA line on a chart that connects all points of equal or constant temperature. (isotopeOne of two or more atoms that have the same atomic number (i.e., the same number of protons in their nuclei) but have different mass numbers. Forms of the same element that have the same number of protons but differing numbers of neutrons. This mass difference gives rise to slightly differing chemical properties for each isotope. Of interest here are the stble isotopes of carbon: carbon-12 (or 12C) and carbon-13 (or 13C), which are stable over timeX and carbon-14, which is a radioisotope and decays with time to an isotope of nitrogen. isotopes in paleoceanographyStable isotopes of some light elements occuring in nature in given ratios fractionated by the biosphere and thereby providing informative signals about the latter. Most useful ratios are 16O/18O; 12C/13C. Marine organisms biomineralize using oxygen in their calcite, etc., and in doing so record the temperature of the reservoir (i.e., the ocean) in the 16O/18O ratio, which is expressed as delta-18O, a departure from an agreed standard. But evaporation removes a bit more 16O -- a lighter fraction -- from the reservoir. That does not matter at geological time scales until that very light fraction is locked up as an icecap, whereupon the reservoir is distorted in the heavier direction. Many believe that that ice effect is not a great distorter in the Eocene; it becomes assertive in the Oligocene. Carbon behaves differently. Photosynthesis removes 12C preferentially, so that calcite skeletons are enriched in 13C. Thus high productivity is signaled as an increased difference between the planktonic record (from the photic zone) and the benthic record (where the light fraction is returned to the system). But when both signals go positive through time that shift signals a removal of organically fixed carbon from the reservoir altogether -- into oceanic sedimpents, becoming a potential source of oil, or into increased terrestrial plant biomass and thence into coals.
jkulhlaupSudden, often catastrophic, flood discharge resulting from the failure of part of a glacier-ice or glacial-drift barrier that forms part of the basin of a glacial lake. >kerogen5Solid bituminous mineraloid substance in oil shales. H komatilte=Volcanic rock containing more than 18 perceny by weight MgO. JKrakatoaTActive volcano, elevation 813 m (2667 ft), which forms an island in West Indonesia between Java and Sumatra (6.102 S, 105.423 E). Its eruption in 1883, which was one of the most violent in modern times, scattered debris and darkened skies over vast areas. Additional eruptions occurred in late 1927 and in the 1960s.
lahar A torrential flow of water-saturated volcanic debris down the slope of a volcano in response to gravity. A type of mudflow. Also known as a "glowing avalanche." landslideAn abrupt movement of soil and bedrock downhill in response to gravity. Landslides can be triggered by an earthquake or other natural causes. Undersea landslides can cause tsunamis. olangleyfThe unit of solar energy relating to the amount which reaches a specific area of the earth's surface. lapilliLiterally "little stones;" round to angular rock fragments measuring 1/10 inch to 2 1/2 inches in diameter, which may be ejected in either a solid or molten state. large-ion lithophile elementsElements with an affinity for oxygen-containing compounds, particularly silicate minerals, and possessing ionic radii larger than most common rock-forming elements. Examples include K, Cs, Th, U, La, Ba. (lateritizationSoil-forming process typical of warm humid climates where in mature landscapes, primary minerals are essentially completely weathered away to form red soils (laterites) of high aggregate stability composed primarily of sesquioxides (oxides and hydroxides of iron and aluminum). latitudeThe location of a point north or south of the equator. Latitude is shown on a map or globe as east-west lines parallel to the equator. lavaMagma which has reached the surface through a volcanic eruption. The term is most commonly applied to streams of liquid rock that flow from a crater or fissure. It also refers to cooled and solidified rock. lava flowAn outpouring of lava onto the land surface from a vent or fissure. Also a solidified tongue-like or shee- like body formed by outpouring lava. lava tubeA tunnel formed when the surface of a lava flow cools and solidifies, while the still-molten interior flows through and drains away. leaking modeA surface seismic wave which is imperfectly trapped so that its energy leaks or escapes across a layer boundary, causing some attenuation or loss of energy. FLg wave The place where two or more plates in the Earth's crust meet. plate tectonicsThe theory that the Earth's crust and upper mantle (the lithosphere) is broken into a number of more or less rigid, but constantly moving, segments or plates. plate tectonicsThe theory that the earth's crust is broken into many large fragments (plates), which move in relation to one another, shifting continents, forming new ocean crust, and causing volcanic eruptions. P PleistoceneThe earlier of the two periods of the Quaternary period, starting 2 to 3 million years before the present and ending about 10,000 years ago. It was a time of glacial activity. A vast amount of evidence has been collected that indicates dramatic oscillations in climatic conditions of global proportion throughout the Pleistocene. It has been well documented that global ice mass has undergone huge fluctuations on the order of 10E19 kg (equivalent to more than 100 meters of sea level) during the last million years. In addition, it has been demonstrated that the concentrations of atmospheric CO2 vary by at least 30% through a glacial cycle, with glacial periods characterized by low pCO2 (~190 ppm) and interglacials by high pCO2 (~280 ppm). Ocean temperaturCe and circulation have also undergone glacial-interglacial change. plugSolidified lava that fills the conduit of a volcano. Plugs (also called volcanic necks) are usually more resistant to erosion than the material making up the surrounding conei and may remain standing as a solitary pinnacle when the rest of the original structure has eroded away. plug domeThe steep-sided, rounded mound formed when viscous lava wells up into a crater and is too stiff to flow away. It piles up as a dome-shaped mass, often completely filling the vent from which it emerged. }plumevVolume of contaminated groundwater that occupies a continuous region of an aquifer and emanates from a single source. Fpluton>A large igneous intrusion formed at great depth in the crust. D
podzolizationSoil-forming process typified by formation of humic acids and leaching of acids and sesquioxides. Continuum of soils developed range from peats, podzol soils (upper mineral soil bleached nearly white by organic acids) to podzolic soils where leaching of s5esquioxides is insufficient to bleach mineral soil. polar motionPath of the earth's spin axis relative to an earth fixed-coordinate system. Movement of the rotation axis relative to geographic (earth-fixed) coordinates, consisting mainly of a slow drift, a 14-month Chandler wobble and a 12-month annual wobble. @polarity chron0Time interval of constant geomagnetic polarity.
polarity zoneStratigraphic interval in which the rocks or sediments carry a magnetization indicating formation in a field of constant polarity. ipositive feedbackVAn interaction that amplifies the response of the system in which it is incorporated. potential energy (gravitational)The stored energy of a substance. Water has a lot of this if there is an elevation difference. Potential energy can be converted to kinetic energy if the water (or other substance) is allowed to move. potentiometric surfaceImaginary surface defined by the levels to which water will rise in wells that are open at the same elevation. The slope of the potentiometric surface determines the horizontal direction of groundwater flow.
precipitation~Any condensed water falling from the atmosphere to the surface of the earth. Common types include rain, snow, sleet and hail. pressure gradientThe rate of decrease in atmospheric pressure per unit of horizontal distance; used to indicate relative pressures on the earth's surface7 and measured in the direction of most rapid decrease.
primary magmaMagma produced by melting a solid precursor. Magma only slightly differentiated in composition from primary magma is called primitive. primary phase fieldqArea or volume on a phase diagram depicting crystal-melt equilibria in which one crystalline phase precipitates. principle of oppositionGraphical technique used to model fractional crystallization of a magma that determines the composition of the extract assemblage. proxy climate indicators\Dateable evidence of a biological or geological phenomenon whose condition, at least in part is attibutable to climatic conditions at the time of its formation. Proxy data are any material that provides an indirect measure of climate and include documentary evidence of crop yields, harvest dates, glacier movements, tree rings, /varves, glaciers and snow lines, insect remains- marine microfauna, isotope measurements: 18O in ice sheets, 18O, 2H, and 13C in tree rings; CaCO3 in sediments; and speleothems. There are three main problems in using proxy data: (1) dating, (2) lag and response time, and (3) meteorological interpretation. Tree rings, pollen deposits from varved lakes, and ice cores are the most promising proxy data sources for reconstructing the climate of the last five millennia because the dating are precise on an annual basis while other proxy data sources may only be precise to +/- 100 years. pumice$Light-colored, frothy volcanic rock,usually of dacite or rhyolite composition, formed by the expansion of gas in erupting lava. Commonly seen as lumps or fragments of pea-size and larger, but can also occur abundantly as ash-sized particles. y pyroclasticZIgneous material erupted explosively as finely pulverized lava (bombs, blocks, pumice, ash and hot gases). pyroclastic flowLateral flowage of a turbulent mixture of hot gases and unsorted pyroclastic material (volcanic fragments, crystals, ash, pumice| and glass shards) that can move at high speed (50 to 100 miles an hour.) The term also can refer to the deposit so formed. quantitative stratigraphyUse of computer-based mathematical methods to calibrate stratigraphic models that with a minimum of information provide maximum predictive potency and include formulation of confidence limits. 'Quaternary periodThe latest period of geologic time, covering the most-recent two million years of the Earth's history. It is divided into two epochs: the Pleistocene -- two million years ago to approximately 10,000 years ago -- and the Holocene -- the period from approximately 10,000 years ago to the present. The Quaternary period is the artificial division of time separating prehuman and human periods. It contains five ice ages and four interglaqcial ages, and temperature indicators seem to show sharp abrupt changes by several degrees.
rayleigh wave*A type of surface wave having a retrograde) elliptical motion at the Earth's surfaceW similar to the waves caused when a stone is dropped into a pond. These are the slowest+ but often the largest and most destructive of the wave types caused by an earthquake. They are usually felt as a rolling or rocking motion and in the case of major earthquakesm can be seen as they approach. Named after Lord Rayleigh, the English physicist who predicted its existence. rechargeThe process by which water is added to a reservoir or zone of saturation, often by runoff or percolation from the soil surface.
recharge areaRegion in which there is a net addition of water to the groundwater system (recharge) as a result of infiltration from surface water bodies or an excess of precipitation over, evapotranspiration and runoff. orecurrence IntervalZThe approximate length of time between earthquakes in a specific seismically active area. reflectivity|The ratio of the energy carried by a wave that is reflected from a surface to the energy of a wave incident on the surface.
regolith reductionDiminishment in volume and mass of parent material to a smaller volume and mass of weathered soil residue as mobile constituents are carried away, in solution or by aeolian transport. c reservoirXAny natural or artificial holding area used to store, regulate, or control a substance. residual enrichmentzIncrease in the enrichment factor of a relatively immobile element by virtue of hydrochemical leaching of mobile species.
reverse fault~General term for a fault dipping between 30 and vertical, and with the hanging wall moving up with respect to the foot wall. reverse weatheringCollection of processes that lead to return of protons consumed in the process of chemical weathering to earth's surface system. Rreversed polarity?Geomagnetic polarity that is opposite to the present polarity. 9rheology/Science of the deformation and flow of matter. rhyoliteVolcanic rock (or lava) that characteristically is light in color, contains 69 percent silica or more, and is rich in potassium and sodium. It is fine grained, which although different in texture has the same composition as granite.
Richter scaleThe system used to measure the strength of an earthquake. Developed by Charles Richter in 1935 as a means of categorizing local earthquakes. It is a collection of mathematical formulas; it is not a physical device. rift systemThe oceanic ridges formed where tectonic plates are separating and a new crust is being created; also, their land counterparts, such as the East African Rift. ring currentElectrical current at about three earth radii from the center of the earth. The current results from charged particles trapped in the geomagnetic field. j ring of fire\The regions of mountain-building earthquakes and volcanoes that surround the Pacific basin. ( rupture zoneThe area of the Earth through which faulting occurred during an earthquake. For very small earthquakes, this zone could be the size of a pinhead, but in the case of a great earthquakebthe rupture zone may extend several hundred kilometers in length and tens of kilometers in width. S wave +Shear, secondary, rotational, tangential, ) equivoluminal, distortional, transverse or shake wave. These waves carry energy through the Earth in very complex patterns of transverse (crosswise) waves. These waves move more slowly than P waves, but in an earthquake they are usually bigger. S waves cannot travel through the outer core beca6use these waves cannot exist in fluids, such as air, water or molten rock. S-waveSecondary wave, a shear or transverse elastic wave, usually the most prominent wave on a seismogram; travels more slowly than P-waves and thus arrives later on seismograms. Rsalt water intrusiontectonic4Pertaining to the deformation of the earth's crust. d teleseismYAn earthquake that is distant (usually more than 20 degrees) from the recording station. Ftelluric currents3Natural electric currents that flow in the ground. cTEM^Transient Electromagnetic Method in which the primary energizing field is a repetitive pulse. utephramMaterials of all types and sizes that are erupted from a crater or volcanic vent and deposited from the air. 8 thermophile+Solute diffuses into warmer bottom waters. tholeliteRelatively silica-rich and alkali-poor basaltic rock containing intermediate to calcic, plagioclase, clinopyroxene, and low-Ca pyroxene. thrust faultGeneral term for a fault dipping between horizontal and 30 and with the hanging wall moving up with respect to the foot wall. Ttill (glacial)DGeneral term for material deposited by a glacier. See also moraine. transcurrent faultOne class of vertical faults with a horizontal displacement vector that does not link two or more plate tectonic scale boundaries. transform faultA class of vertical faults with a horizontal displacement vector that does not link two or more plate tectonic scale boundaries.
translocationPhysical or chemical migration of suspended particles or aqueous solutes by moving water in a hydrochemical system or by animals and plants. ?translocation crossover,Soil depth at which mass accumulation of an element by downward translocation changes from positive to zero and then to negative, thereby separating an upper soil system dominated by invasion of foreign detrital minerals from a lower, less contaminated, soil system referred to as saprolite. e travel timeXThe time required for a wave train to travel from its source to a point of observation. tsunamiLiterally "harbor wave" in Japanese. Tsunamis are great sea waves produced by a submarine earthquake, volcanic eruption or large landslide. Tsunamis can cause great damage due to flooding of low coastal areas. +tuff%Rock formed of pyroclastic material. turamElectromagnetic survey method in which the energizing source is a long, grounded, insulated cable or a large, rectangular, horizontal loop excited by one or more frequencies in the range of 100-1000 Hz. Zunconsolidated*Loosely arranged, not cemented together, so particles separate easily. xunsaturated zonefZone between the land surface and the water table in which fluid pressures are less than atmospheric. LvarveA layer of sediment deposited in lakes during one year. Each layer consists of two parts, which are deposited at different seasons and which differ in color and texture; thus the layers can be counted and measured. In a complete series the number of layerEs gives the date on which the ground was vacated by retreating ice. ]ventWThe opening at the earth's surface through which volcanic materials reach the surface. vesicular basaltHoles and other openings in basaltic flow which are the result of trapped gas bubbles. Vesicles are often filled at a later date with a wide variety of materials, including quartz, agate, zeolites, and many other minerals. viscosityA measure of resistance to flow in a liquid (molasses in January has high viscosity while molasses in August has lower viscosity). volatilesElements that are soluble in magmas at elevated pressure and temperature that exsolve as gas from magmas during ascent and eruption at the earth's surface. They include sulfur, water, carbon dioxide, chlorine and fluorine. volcanic aerosolVery small (microns to fraction of micron in diameter) particles or droplets, composed mainly of sulfuric acid and water, produced by the gas-to-particle conversion of sulfur dioxide gas to sulfuric acid in the volcanic eruption plume. mvolcanic front]Elongate zone of maximum volcanic activity that defines the main volcanic (or magmatic) arc. '
volcanic neckSolidified lava that fills the conduit of a volcano. Volcanic necks (also called plugs) are usually more resistant to erosion than the material making up the surrounding cone hand may remain standing as a solitary pinnacle when the rest of the original structure has eroded away. water cycleThe transfer of water between numerous temporary storage reservoirs. These include the ocean, rivers and streams, glacial ice, groundwater and the atmosphere. R water tableESurface along which fluid pressure is equal to atmospheric pressure. rweathering (surface)\Weathering includes the processes which mechanically and chemically wear and fragment rock. weights of evidence modelingEstimation of posterior probability that a hypothesis holds true from its prior probability and a combination of weights associated with presence or absence of features supporting the hypothesis. wireline loggingMeasurement of depth variations (logs) of physical properties using a tool or sonde deployed by means of a conducting cable (wireline). xenolithRock sample with mineralogy foreign to the igneous host in which it occurs. Thought to be a fragment of wall rock from volcanic conduits in the deep lithosphere rapidly transported to the surface during eruptions. zone of ablation (or wastage)