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GEOLOGY [ DICTIONARY ]
______________________________________
ORTHO- (prefix) a metamorphic rocke derivied from an igneous rock
PETRO- (prefix) related ro rocks
-ZOIC (suffix)
__ A __
ABLATION - loss of ice at the lower end of a glacier ;
INDEX - goemorphology - glaciology
ABRASION - is a form of physical weathering where rocks tumble over one another
rounding corners from angular, to sub-rounded, to rounded ;
INDEX - goemorphology - weathering
ABSOLUTE TIME - the geologic age of a fossil, rock, geologic feature, or event
given in years ; although the time may NOT be as accurate or precise in the
strictest use of the term ; INDEX - historical geology
ACCRETE - To add terranes (small land masses or pieces of crust) to another,
usually larger, land mass ; INDEX - goemorphology - tectonics
ACID MINE DRAINAGE - a toxic hazard where pyrite, an iron sulfide, is exposed
and reacts with air and water to form sulfuric acid and dissolved iron.
The hazard can be further exascerabeted by certain bacteria.
ACTIVE MARGIN - an area of seismic activity and active volcanoes or growing
mountians on the leading edge of a continent that is "crashing" into an
oceanic plate ; S.A: (continent-ocean) convergent plate boundary ;
INDEX - goemorphology - tectonics
ALPHA DECAY - Ejection of two protons and two neutrons (Helium nucleus) from
the nucleus ; INDEX - historical geology
ALPHA EMISSION (radiometic dating) ; INDEX - historical geology
ALPINE GLACIER - SYN. VALLEY GLACIER
AMPHIBOLE - A family of silicate minerals forming prism or needlelike crystals.
Amphibole minerals generally contain iron, magnesium, calcium and aluminum
in varying amounts, along with water.
ANTICLINE - A fold of rock layers that is convex upwards ;
INDEX - structural geology
ASTHENOSPHERE - the part of the mantle that lies below the lithosphere at 100-to-
200 km below the surface. This highly viscous layer can extend to 700 km and
is involved in plate tectonic movement ; INDEX - physical geology
__ B __
BED LOAD - material that moves by rolling, sliding, and/or saltating (hopping) ;
INDEX - goemorphology - erosion
BETA DECAY - Transformation of a neutron into a proton by ejecting an electron
from one of the neutrons in the nucleus ; INDEX - historical geology
BETA EMISSION - is the result of beta decay ; INDEX - historical geology
BIOSTRATIGRAPHY - The study of rock layers based on their fossils including
distribution, environment of deposition, and age ; S.A: fossil correlation
__ C __
CARBINATION - the reaction of carbonate and bicarbonate ions with minerals.
Carbonation is especially active when the reaction environment is abundant with
carbon dioxide ; INDEX - goemorphology - weathering
CATASTROPHISM - is the idea that geomorphic changes have occurred due to violent
or unusual events ; floods, earthquakes or lava flows ; INDEX - physical geology
CHEMICAL WEATHERING - The process that changes the chemical makeup of a rock or
mineral at or near the Earth’s surface ; INDEX - goemorphology
CLEAVAGE - The tendency of a mineral to break along weak planes.
CONTACTS - boundaries between different rock types or formations ;
INDEX - field geology
CONTINENTAL DRIFT - A hypothesis proposed by Alfred Wegener suggesting that the
continents are not stationary, but have 'drifted' through time ;
INDEX - goemorphology - tectonics
CONTINENTAL MARGIN - The ocean floor from the shore of continents to the abyssal
plain ; INDEX - physical geology - geography
CONTOUR INTERVAL - is the consistent vertical change on a topographic map ;
INDEX - field geology
CONTOUR LINES - a visible line on a topographic map connecting points of equal
elevation ; INDEX - field geology
CONVERGENT PLATE BOUNDARY - A boundary in which two tectonic plates collide ;
INDEX - goemorphology - tectonics
COVALENT BOND - the sharing of electron pairs between atoms ; S.A: minerals,
elements.
CRATON - A part of the Earth's crust that has attained stability and has been
little deformed for a long period of time.
CREEP - slow dowhill movement of regolith due to seasonal expansion and
contraction that results from freeze / thaw and wet / dry cycles ;
S.A: mass wasting ; INDEX - geomorphology - erosion
CROSS SECTION - vertical slices into the earth that are used to interpret the
geology at depth. The geological data (contacts, dips of formations, etc.)
are projected from the surface into the cross section to predict what might
be down there ; INDEX - field geology
CRUST - The outermost layer of the Earth, varying in thickness from about 10 KM
below the oceans, to 65 kilometers below the continents ;
INDEX - physical geology
CRTYSTAL FORM - the geometric shape of a crystal.
CRTYSTAL HABIT - refers to the general crystal forms and combinaton in which
a mineral habitually forms.
__ D __
DAUGHTER ATOMS (radiometic dating) ; INDEX - physical geology
DEEP-FOCUS EARTHQUAKE - is an earthquake with a hypocenter exceeding 300 KM
in depth almost exclusively found at convergent plate boundaries. The
deepest recorded was just over 700 KM ; INDEX - physical geology
DIFFERENTIAL EROSION - variable rates of rock weathering associated with
resistance of rock to weathering. While softer are eroded and carried away,
harder and more resistant rocks remain to form ridges, hills, or mountains ;
SYN. DIFFERENTIAL WEATHERING ; INDEX - geomorphology
DIFFERENTIAL WEATHERING - SYN. DIFFERENTIAL EROSION
DISCRETE CONTACT - a map-unit boundary that is individually distinct; that is,
the transition between geologic units is abrupt enough to be recognized and
delineated easily on the map ; INDEX - field geology - geologic map
DISSOLVED LOAD - a significant portion of the total stream load where chemically
dissolved sediment combines with bed load & sediment load within a stream ;
INDEX - geomorphology - erosion
DISSOLUTION - the hydrolysis of limestone and rocks high in salt ; S.A: hydrolysis ;
INDEX - geomorphology - weathering
DIVERGENT PLATE BOUNDARY - tectonic plate margins where forces deep within the
earth are forcing tectonic plates apart creating rift zones ; S.A: MOR ;
INDEX - goemorphology - tectonics
DOUBLY PLUNGING FOLD - fold axis is plunging in two opposite directions,
results in a flattened oval pattern, or a double V-shaped pattern <<< >>>> ;
INDEX - structural geology
__ E __
ECONOMIC GEOLOGY - is concerned with earth materials that can be used for
economic and/or industrial purposes. These materials include precious and
base metals, nonmetallic minerals, construction-grade stone, petroleum
minerals, coal, and water.
EFFUSIVE ERUPTION - a steady non-explosive flow of lava.
EPICENTER - Point on the Earth's surface directly above the focus of an
earthquake ; INDEX - physical geology
EROSION - sediment transport by wind, water, glaciers, or gravity ; S.A: mass
wasting / landslide ; INDEX - goemorphology
EUSTASY - a change in sea level throughout the world caused by glaciation or
tectonic plate movement ; S.A: isostacy ; INDEX - physical geology
__ F __
FEILD GEOLOGY - a geologic practice that applies first-hand observation in the
field.
FLANK ERUPTION - an eruption from the side of a volcano rather than the summit ;
SYN. LATERAL ERUPTION
FORENSIC GEOLOGY - interpretation of geological evidence at crime scenes
FORMATION - a distinctive body of rock that is large enough to symbolize on a
geologic map ; S.A: rock unit, (rock) group, member ;
INDEX - field geology
FRACTIONAL SCALE - a map feature that denotes the mathematical reduction of
distance usually the expression 1:xxxx ; Sg. 1:1000 - could mean 1-to-1000
feet, kilometers, ect. ; INDEX - field geology
FROST WEDGING - a form of physical weathering that breaks rocks by liquid water
freezing within a pore space and exerting an outward force ; SYN. ICE WEDGING
INDEX - geomorphology - weathering
__ G __
GEOLOGIC CONTACT - is where one rock type touches another - there are 3 types of
contacts ; depostional contact, intrusion contact, unconformable contact ;
INDEX - field geology
GEOLOGIC MAPS - Maps that show the types and ages of rock of an area ;
INDEX - field geology
GEOLOGIC TIME - combines the concepts of "absolute time" and "relative time" in a
scale that covers the roughly 4.6 billion years of Earth's history ;
INDEX - historical geology
GEOMAGNETISM - the study of the dynamics of earth's magnetic shield ;
INDEX - earth science - geology ;
GEOTHERMAL GRADIENT - is the rate of increasing temperature with respect to
increasing depth in the Earth's interior. Away from tectonic plate boundaries,
it is about 25–30 °C/km ; INDEX - physical geology
GRADIENT (topographic) - is the change in elevation divided by the distance usually
reported in feet per mile (ft/mile) ; INDEX - field geology
GRADATIONAL CONTACT - a map-unit boundary that is diffuse; that is, the transition
between geologic units is gradual enough that it cannot be recognized or
delineated easily on the map ; INDEX - field geology - geologic map
__ H __
HISTORICAL GEOLOGY -(see.also.paleogeology) is a discipline that uses the
principles and techniques to reconstruct the geological history of Earth.
HYDRATION - an inorganic chemical reaction where the rigid attachment of H+ and
OH- ions to a reacted compound. In many situations the H and OH ions become
a structural part of the crystal lattice of the mineral ;
INDEX - goemorphology - weathering
HYDROLYSIS - the reaction between mineral ions and the ions of water (OH- and H+).
Its the primary method of weathering silicate and alumino-silicate minerals
because of their electrically charged crystal surfaces ; S.A: DISSOLUTION ;
INDEX - goemorphology - weathering
HYDROGEOLOGY - the study of subsurface waters (groundwater) and the related
geologic aspects of surface waters.
HYPOCENTER - the point within the earth where an earthquake rupture starts ;
S.A: epicenter ; INDEX - physical geology
__ I __
ICE WEDGING - SYN. FROST WEDGING
ICE WEDGE POLYGON - the most common ground pattern in the Arctic due to freeze
thaw cycles ; INDEX - geomorphology
ICHNOLOGY - The study of trace fossils ; INDEX - field geology
INDEX CONTOUR - are the darkened contour lines on a topographic map that add
contrast for better visual representation of vertical gradient ;
INDEX - field geology
INDEX FOSSILS - are fossils that are particularly useful in biostratigraphic
correlation. These are widespread geographically and only live for a short
time geologically ; INDEX - historical geology
ISOSTASY - a theory which states that the earth's crust behaves like blocks
floating on the mantle in a state of equilibrium - thus falling and rising
as material is either added or removed ; S.A: eustasy ;
INDEX - physical geology
__ J __
__ K __
KEY BED - an easily identifiable stratigraphic marker bed within a geologic unit.
Commonly it is too thin to depict as a map-unit area at most map scales, and
so it usually is classified as a planar geologic feature ;
INDEX - field geology - geologic map
__ L __
LATERAL ERUPTION- SYN. FLANK ERUPTION
LAW OF CROSS-CUTTING RELATIONSHIP - a relative dating concept in historical
geology which states that older rock must exist before a cross-cut occurs ;
INDEX - historical geology
LAW OF INCLUSION - a relative dating concept in historical geology which states
that an inclusion must be older than the rock it becomes an inclusion in ;
INDEX - historical geology
LAW OF LATERAL CONTINUITY - a relative dating concept in historical geology
which states that horizontal deposition contiues laterally without an
abrupt end ; INDEX - historical geology
LAW OF ORIGINAL HORIZONTALITY - a relative dating concept in historical geology
which states that horizontal deposition preceeds all other processes ;
INDEX - historical geology
LAW OF SUPERPOSITION - a relative dating concept in historical geology which
states that the youngest rock layers exist at the top of a horizontal
stratagraphic column and become progressively older as you move down the
column ; INDEX - historical geology
LITHOSPHERE - is comprised of the crust and upper portion of the mantle with a
thickness between 50 & 150 km ; INDEX - physical geology
__ M __
MAGMATIC ERUPTION - gas-driven explosion of magma and tephra.
MASS WASTING - an erosional process due to gravity ; S.A: landslide ;
INDEX - goemorphology - erosion
MECHANICAL WEATHERING - SYN. PHYSICAL WEATHERING
MEMBER - subdivision of a formation ; S.A: rock unit
MINERAL - a naturally occuring inorganic chemical compound with a regular internal
structure ; S.A: petrology - rock
MOLD (see.also. cast) - is created when a shell is buried and is later dissolved
by underground water leaving and open space.
MONOCLINE - a step-like fold in a rock strata ; INDEX - structural geology
__ N __
NORMAL FAULT - faults in which crustal block above the fault plane (hanging
wall) move down relative to crustal block below the fault plane (foot
wall) ; INDEX - structural geology
NONCONFORMITY - exists when sedimentary rocks lay above metamorphic or igneous
rock layers. Therefore a time gap (unconformity) exists due to the unknown
amount of erosion ; INDEX - historical geology
__ O __
OBLIQUE-SLIP FAULT - a fault with both vertical and horizontal components of
movement ; INDEX - structural geology
OCEANIC CRUST - The Earth's crust which is formed at mid-oceanic ridges,
typically 5 - 10 KM thick ; INDEX - physical geology
OCEANIC LITHOSPHERE - typically the 50-100 KM of mafic crust and ultramafic
upper mantle that is no older that 200 million years since it is created
at divergent tectonic boundaries and recycled at subduction zones ;
INDEX - physical geology
OROGENY - The tectonic processes of folding, faulting, and uplifting of the
earth’s crust that result in the formation of mountains.
OUTCROP - Any place where bedrock is visible on the surface of
the Earth ; INDEX - field geology
OXIDATION - a form of chemical weathering where oxygen reacts with other
elements in the rock ; INDEX - goemorphology - weathering
__ P __
PALEOMAGNETISM - a branch of geophysics concerned with the magnetism in rocks that was
induced by the earth's magnetic field at the time of their formation ;
INDEX - historical geology
PARACONFORMITY - a near conformity disconformity with no discernible erosional
surface, but a distinct gap in the fossil record ; INDEX - historical geology
PASSIVE MARGIN - is a transition between oceanic and continental lithospheres
that is not a plate boundary ; INDEX - geomorphology - tectonics
PELEAN ERUPTION - characterized by one massive explosion with a tall column
and fast moving pyroclastic flow.
PERIGLACIAL (zone,region,environment) - landforms and processess at the edges of
glaciated areas ; S.A: permafrost ; INDEX - geomorphology - glaciology
PERMAFROST - organics and soil (regolith) that remains frozen (0 C) for two or more
years ; INDEX - geomorphology
PERMINERIZATION - Fossilization process that occurs when minerals, carried by
ground water, enter and harden in the pores of an organism’s structures.
PETROLOGY - study of rocks, including information on chemistry; classification;
mineralogy, occurrence, shape and structure of rock masses (petrography),
and rock origins (Petrogenesis) ; INDEX - physical geology
PHANEROZOIC - The geologic eon that includes the interval of time from
approximately 543 million years ago to the present, comprising the Paleozoic,
Mesozoic, and Cenozoic eras ; INDEX - historical geology
PHREATIC ERUPTION - also called a steam-blast eruption where magma heats ground
or surface water into a blast of steam, water, ash and rock.
PHREATOMAGMATIC ERUPTION - results from interaction of water with magma
PHYSICAL GEOLOGY - is the study of the earth's rocks, minerals, and soils and
how they have formed through time.
PHYSICAL WEATHERING - a process that break rocks without changing its chemical
compostion ; SYN. MECHANICAL WEATHERING ; INDEX - goemorphology
PLINIAN ERUPTION - SYN. VULCANIAN ERUPTION
PLUNGING FOLDs - folds in which the fold axis is dipping; the direction the fold
axis is dipping is called the plunge direction ; INDEX - structural geology
PRIME MERIDIAN - a map feature to establish a geographic grid between E-&-W
longitude. The prime meridian, or 0 degrees E-W longitude, was established
at Greenwich, England in 1884 ; INDEX - field geology
__ Q __
__ R __
REGOLITH - soil, sediment and broken rock immediately above a rock surface.
RELATIVE DATING - a method of determining which rocks are older or younger in a
large-scale geographic feature ; INDEX - historical geology
RELIEF (topographic) - is the numerical difference between the highest and lowest
elevation on a topographic map ; INDEX - field geology
REVERSE FAULT - faults in which crustal block above the fault plane (hanging wall)
moves up relative to crustal block below the fault plane (foot wall) ;
S.A: thrust fault ; INDEX - structural geology
RIDGE PUSH - a source of potential energy for tectonic plate movement due to the
high ridges formed at divergent plate boundaries. Vertical gravity force
moving down the ridge tranlates to a lateral force due to the curvature of
earth to supply some energy for tectonic plate movement ;
INDEX - geomorphology - tectonics
ROCK - a solid aggregate of one or more minerals ; S.A: coal, halite - rock salt,
ice.
ROCK CYCLE - The process through which one type of rock (igneous, sedimentary, or
metamorphic) is converted into another.
ROCK GLACIER - a mass wasting erosion process similar to glacial erosion except
the ratio of ice and rock are reversed ; INDEX - goemorphology - erosion
(rock) GROUP - two or more (rock) formations.
ROCK UNIT - three-dimensional bodies of rock characterized by a particular
physical attribute (rock type, color, etc.) ; INDEX - field geology
__ S __
SALTATION - a sediment transport process that moves large material by a hoping or
bouncing motion ; S.A: traction ; INDEX - goemorphology - erosion
SALT CRYSTALLIZATION - a form of physical weathering similar to frost wedging.
This type of weathering occurs when salt water penetrates rock pores and
generates salt crystals as the water evaporates. The crystal growth produces
an outward force ; INDEX - goemorphology - weathering
SEA-FLOOR SPREADING - The process of adding to the Earth's crust at mid-ocean
ridges as magma wells up and forces previously formed crust apart ;
INDEX - goemorphology - tectonics
SEDIMENT LOAD - particles that are too large to be dissolved, but small enough
to stay suspended. The ultimate size of the particle carried in the sediment
load is dependent upon the water velocity ; INDEX - goemorphology - erosion
SLAB PULL - Where gravity pulls a cold subducting plate down into the mantle at
a subduction zone. Additional energy is added by mantle convection currents
to create "slab suction" ; INDEX - goemorphology - tectonics
SLUMPING - a type of mass wasting erosion often called a slope failure ;
INDEX - goemorphology - erosion
SOLIFLUCTION - similar to creep, this form of mass wasting occurs when water
saturated soil, like thawing permafrost, slowly moves downhill to create
distinctive features called solifluction lobes ; INDEX - goemorphology -
erosion
SPHEROIDAL WEATHERING - a type of chemical weathering that rounds off angluar
rock surfaces due to the larger surface areas ; INDEX - goemorphology
STENO's LAWS OF STRATIGRAPHY - Nicolaus Steno, a Danish geologist, proposed a
set of rules to describe patterns in rock layers ; INDEX - historical geology
STRATUM - a single rock bed ; INDEX - field geology
STRATA - a group of rock beds ; INDEX - field geology
STRATIGRAPHIC COLUMNS - vertical representations of thethicknesses of the
various formations in a given area ; INDEX - field geology
STRATIGRAPHY - The study of rock layers, especially their distribution,
environment of deposition, and age ; INDEX - field geology
STREAM LOAD - the solid matter carried by a stream as bed shear stresses increase
to remove material from the stream bed ; INDEX - goemorphology - erosion
STROMBOLIAN ERUPTION - a volcanic eruption characterized by short-lived,
explosive eruptions of lavas with intermediate viscosity that are driven
by bursting gas bubbles in the magma. Often result in high arching
volcanic bombs and lapilli ; S.A: cinder cones, scoria
STRUCTURAL GEOLOGY - the origin of geological features produced by stresses
within the earth's crust (such as folds and faults)
SUBDUCTION - A geologic process in which one edge of one crustal plate is
forced below the edge of another ; INDEX - goemorphology - tectonics
SURTSEYAN ERUPTION - a phreatomagmatic eruption that takes place in shallow seas
or lakes.
SYNCLINE - A fold of rock layers that is convex downwards ; INDEX - structural
geology
__ T __
TERRANE - A general term used to refer to a piece of the crust that is
usually smaller than a continent but larger than an island ;
INDEX - physical geology
THEORY OF PLATE TECTONICS - is the "grand unifying theory" of geology.
Sg. evolution - biology ; gravity - physics ; INDEX - goemorphology
THRUST FAULT - a reverse fault with very low angle, or very gently inclined
fault plane ( < 30 degrees) ; INDEX - structural geology
TRACTION - a sediment transport process that moves large material by rolling
or sliding across the bottom of a river or stream bringing interaction with
the sbustratum ; S.A. saltation ; INDEX - goemorphology - erosion
TRANSFORM PLATE BOUNDARY - is a tectonic margin where two plates are sliding
past each other creating seismic zones like the San Andreas fault ;
INDEX - goemorphology - tectonics
__ U __
UNCONFORMITY : ANGULAR UNCONFORMITY, DISCONFORMITY ; INDEX - historical geology
UNIFORMITARIANISM - is the idea that geomorphic processes occuring today are
the same as those in the past - these processes are continuous and
"uniform". This theory incorporated and replaced the idea of
"catastrophism" ; INDEX - physical geology
__ V __
VALE CURVE - a curve that represents the rise and fall of sea level ;
INDEX - geomorphology
VERTICAL EXAGGERATION - is a topographic profile feature that uses a smaller
fractional scale for the vertical axis than the fractional scale for the
horizontal axis to create a more dramatic representation of topographic
relief ; INDEX - field geology
VESUVIAN ERUPTION - can last for hours or days with the highest explosive
columns that expand and mushroom at the top ; SYN. PLINIAN ERUPTION
VOLCANIC EXPLOSIVITY INDEX - a relative measure of the explosiveness of volcanic
eruption from 0-to-8 developed by USGS in 1982.
VULCANIAN ERUPTION - a highly explosive event with columns reaching as high as
10km. The highly viscous lava is andesitic to dacitic rather than basaltic.
__ W __
WADATI-BENIOFF ZONE - is a planar zone of seismicity associated with subducting
tectonic plates. A planar zone where deep-focus earthquakes can occur ;
INDEX - goemorphology - tectonics
WEATHERING - two primary processes that breaks large rock into progressively
smaller rocks and then soil ; S.A: chemical weathering, physical weathering,
erosion ; INDEX - goemorphology
__ X __
__ Y __
__ Z __
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