Note: All reference sources consulted in compiling this glossary are found at the end. Where the definitions are quoted verbatim the appropriate abbreviation is listed in brackets after the definition.

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A -- C

ablation:  in the astronomical sense it is the removal by heating and vaporization of the surface material of a meteorite as it passes through the atmosphere. In the glaciological sense it is the process by which the terminus of a glacier loses ice or snow either through melting and removal by meltwater streams, or by calving if the glacier terminates in a body of water.    

allochthonous:  Having originated outside the area in which it now occurs.

alluvial:  Pertaining to or composed of alluvium, or deposited by a stream or running water.

alluvium:  A general term for detrital deposits made by streams (running water) on river beds, flood plains, and alluvial fans; especially a deposit of silt or silty clay laid down during a flood.

alluvial fan:  An outspread, gently sloping mass of alluvium deposited by flowing water, especially in an arid or semi-arid region where a stream issues from a narrow canyon mouth onto a plain or valley floor. Viewed from above it has the shape of an open fan, the apex being at the valley mouth. 

anastomosing:  A braided stream which forms diverging branches that recombine, separate and converge again repeatedly to form a network or maze-like pattern. It frequently occurs where a stream or river flows over an excessively sediment filled valley. The Channeled Scabland of Washington displays a gigantic pattern of anastomosing channels cut into the basalt bedrock and provides convincing evidence for the reality of catastrophic megafloods.

anticline:  An arched, convex upward fold in bedrock strata resulting from regional  compression. The oldest layers are found at the center, or axis, of the anticline. The two sides of the upfolded anticline, called limbs, dip, or tilt, downwards away from the axis. When the rock strata is upfolded it fractures along the axis of the fold creating a zone of weakness that is readily exploited by erosional forces. These often evolve into valleys over time. An anticline can be thought of as the opposite of a syncline.

Apollo asteroids:  Asteroids whose orbits cross that of the Earth. There are presently about 240 of them known to astronomers. The largest one known is 1866 Sisyphus with a diameter of about 10 km (6 miles).

asteroid:  One of the many small celestial bodies in orbit around the sun. Most asteroids are found in a belt between Mars and Jupiter.

astrobleme:  An ancient, deeply eroded erosional scar formed by the collision of a cosmic body with the surface of the Earth. It is usually characterized by a roughly circular shape and has associated effects of intense shock such as highly disturbed rocks, shatter cones, shocked quartz etc. An astrobleme is usually eroded to the point where it has lost the classic bowl shaped form of a younger impact crater and it is often buried under younger sedimentary rocks. The term literally means “star wound.”

basalt:  A fine grained igneous rock of mafic composition. Basalts are commonly found as lava flows, issuing from vents or fissures. They are highly fluid which allows them to flow for great distances. Continued, multiple extrusions can form vast layered piles of basalt thousands of feet thick and thousands of square miles in extent. On cooling it forms characteristic hexagonal columns. Vast provinces of basalt such as the Siberian Traps and the Deccan Traps of India a associated with major geological boundaries. 

Beringia:   The geographic area of western Alaska, the Aleutians, and eastern Siberia that was connected during Cenozoic ice ages when sea level was lowered due to the growth of glaciers.

bolide:  A very bright fireball that breaks up during atmospheric entry. Also any projectile of extraterrestrial origin.

bone bed:  Any sedimentary stratum in which fossil bones are found in abundance. Often accompanied by other organic material such as scales, teeth and coprolites.

Boreal:  A climatic zone characterized by long, cold, snowy winters and short summers. The term is typically applied specifically to coniferous forests of the northern hemisphere. The Latin term borealis means northern.

breccia:  A course-grained clastic rock, composed of broken, angular fragments of other rocks, typically cemented together in a fine grained matrix. Breccia can form through several means, including landslides, volcanic eruptions or crushing of rock along fault lines. It is now often associated with evidence of shock metamorphism, and this association convincing evidence for hypervelocity cosmic impact. When numerous bones of extinct animals are found within the rock it is referred to as bone breccia.

caldera:   A circular, steep sided depression that remains in the aftermath of an explosive eruption and collapse of a composite volcano. A caldera may sometimes contain a lake such as found at Crater Lake, Oregon, the remnant of Mt. Mazama, which erupted about 6,500 years BP.

carbonaceous chondrite:  A primitive class of stony chondritic meteorites containing oxidized minerals and organic compounds.

cataract:  a descent of water over a steep surface; a waterfall, esp. one of considerable size. Also, any furious rush of water, a deluge. [ACD] The term has also come to be applied to the typical horseshoe shaped erosional form imparted to the steep rock surface over which the water falls. An example is the cataract of Niagara Falls, esp. “Horseshoe Falls”  on the Canadian side. Dry Falls Cataract in the Channeled Scabland is another spectacular example.

catena:  The name given to chains of craters formed on the surfaces of planets and satellites by the multiple sequential impacts of a chain of cosmic bodies, probably the result of the fragmentation of larger parent body. A scenario similar to catena producing events was witnessed by astronomers in July,1994 when a chain of 21 cometary fragments of Shoemaker/Levy 9 impacted Jupiter over a period of 6 days. Catena observed today on the surfaces of Mars, the Moon, Callisto, etc. are produced from fragments that are much more closely spaced than those of Shoemaker/Levy 9, which makes them stand out much more prominently against the background of craters than if they were spaced farther apart. It is likely that when astronomers began hunting catena in earnest that many more of them will be discovered hiding amongst the thousands of craters which appear to be spaced randomly over the surface of the planet or satellite.

chondrites: The most common type of stone meteorite; contains small, glasslike spheres of melted rock called chondrules. [UTU] Includes the class E, H, L, and LL chondrites. 

clastic:  A sedimentary rock texture consisting of broken fragments of pre-existing rock. [T & L] A clast is an individual part or single constituent of a sedimentary rock, produced by the physical disintegration of a larger mass. [DOPG]

coesite:  a dense polymorph of silica formed only under pressures between about 25 and 100 kilobars, first produced in a laboratory in the early 1950’s and later discovered associated with many impact craters and astroblemes. It is now recognized as an indicator of impact metamorphism, as this is the only known natural process capable of producing the extreme pressure necessary for its formation at or near the Earth’s surface.

colluvium:  A general term applied to loose and incoherent deposits, usually at the foot of a slope or cliff and brought there chiefly by gravity. Talus and cliff debris are included in such deposits.

coma: The diffuse envelope of dust and gas surrounding the nucleus of a comet; the gas and dust are liberated from the nucleus as it draws near to the Sun.  [UTU]

colonization:   The immigration and establishment of a species into a new habitat that has been depopulated due to environmental changes, typically of a catastrophic nature.

Cordilleran ice sheet:  The smaller of the two great North American ice sheets during the Wisconsin ice age. It covered the entire region that is now British Columbia from the Pacific Ocean on the west to the Canadian prairies east of the Rocky Mountains, from the Yukon Territory on the north to south of the 49th parallel into the states of Washington, Idaho and Montana.

coulee:  Originally a French term. A dry or intermittent stream valley, esp. a long trenchlike gorge, frequently with steep sides that once carried glacial meltwater.  Typically found in the northwestern USA. The larger coulees are abandoned channels of catastrophic meltwater flows. The greatest example of such a feature is Grand Coulee, in Washington State, from which Grand Coulee dam derives its name.

Cretaceous:  The name of the third and final period of the Mesozoic Era. It commenced about 140 million years BP and terminated about 66 million years BP with one of the greatest mass extinction events in the history of the Earth.

cross bedding: Inclined sedimentary layers, either unconsolidated or lithified, that are deposited by water currents. The direction of tilt, or dip, is an indication of the direction of the current flow.

current ripple:  In the microscale - a ripple mark in sand or mud produced by the action of a current flowing steadily in one direction. The ripples typically form sub-parallel ridges with a longer gentler slope facing the direction of the current flow and a steep face on the lee, or downcurrent side. In the macroscale giant current ripples form relict, or fossil features in the landscape that were produced by catastrophic palaeofloods. Their internal composition is generally composed of gravel to boulder size sediment, indicative of the great transporting power of the flood currents.

D -- J

denudation: A general term that refers to all processes that cause degradation of the landscape: weathering, mass movement, erosion, corrosion, abrasion and transport. [Geosystems]  In general, a term used to denote the action of laying bare by the process of washing away of surface materials. [DOPG]

Diluvialism:  An idea prevalent in the 18th and 19th centuries that Earth’s surface in its modern form was shaped primarily by the Biblical flood of Noah. With the rise of the glacial theory of Agassiz and others about the mid 19th century Diluvialism was mostly abandoned. However, a new form of Diluvialism has arisen with the discovery of two processes – catastrophic paleofloods typically associated with deglaciation, and giant tsunamis, probably resulting from asteroid or comet impacts into the world’s oceans.

drift:  A general term for all rock material transported by glaciers and deposited directly from the ice or through the agency of meltwater. It is generally applied to Pleistocene deposits in large regions that no longer contain glaciers. The term originated in the 19th century and was applied to deposits usually assumed to have been deposited by large floods.

drumlins:  Depositional features associated with continental ice sheets. They are smooth elongate hills which typically occur in parallel clusters. They can range in height from about 50 feet up to about 160 feet in height. (15 to 50 meters) Drumlins can range up to about a kilometer in length and typically have a steep side and a more gradual side. The steep side faces in the direction from which the glacial ice came. In older ideas of drumlin genesis it is assumed that they formed by plastic deformation under the glacial ice itself, probably during its advance over previously deposited till. In recent decades many drumlin fields have been interpreted as forming by subglacial sheet floods flowing under high pressure, rather than formation through direct action of glaciers themselves. As this idea is confirmed it lends credibility to the idea of catastrophic glacial melting.

ejecta: The material thrown radially outward from an impact crater during its formation. The ejecta blanket is the mantle of ejecta material surrounding the impact crater and covering the ground surface that existed at the time of impact.

ellipse: A closed curve, one of the family of conic sections, that describes the orbital motion of the planets, the satellites of planets and the short period comets.

englacial:  Contained, embedded, or carried within the body of a glacier or ice sheet; said of meltwater streams, till, drift, moraine, etc.

epoch: A unit of geologic time which is a subdivision of a Period.

erratic:   A boulder, often large, which is found in an area where it is not native. The assumption has been that an erratics are transported by glacial ice and are a relict of past ice ages. However, it is now recognized that some erratics have been transported by catastrophic floods, often by icebergs being carried in the flood waters.

esker:  A serpentine ridge composed of drift deposited by a stream flowing beneath the ice of a stagnant or retreating glacier and left behind when the ice melted. (DOGT) 

eustacy:  A change of sea-level that occurs everywhere throughout the world, due not to movement of the land but to an actual rise or fall of the ocean itself. [DOPG] It is recognized that eustacy is controlled by the growth and decay of ice sheets during transitions into and out of ice ages. As glaciers grow, worldwide sea-level falls, as glaciers shrink, sea-level rises. Changes in the geometry of the worlds ocean basin as the result of plate tectonic processes also undoubtedly play a role in eustatic changes in sea level but it is not as clear cut as the glacially controlled effect.

fluvial:  Processes associated with streams, river or water flow; comes from the Latin fluvius for “running water” or “river”

glaciofluvial:  A term referring to the processes and landforms related to the combined action of glaciers and glacial meltwater.

greenhouse effect:  the effect whereby radiatively active gases such as carbon dioxide, water vapor, methane and chlorofluorocarbons (CFCs) transmit shorter wavelength solar energy allowing it to penetrate the atmosphere to be absorbed by materials of the Earth’s surface. The same gases will in turn absorb the longer wavelength infrared heat energy reradiated from the Earth. This causes the heat to be retained in the atmosphere, thus producing a general warming of the climate.  

hanging valley:  a valley tributary to a main trunk valley which has been eroded and deepened by the presence of a glacier which has since disappeared. The tributary valley becomes truncated in the process and its mouth is left hanging above the floor of the main valley. Spectacular examples of this are found in Yosemite Valley, California, USA. It is now also been recognized that very similar truncation can occur as the result of catastrophic floods overdeepening the main valley. Examples of this can be found along the lower Columbia Gorge, where a series of waterfalls drop from hanging cataracts 400+ feet above the river.

H-chondrites:  A class of chondritic meteorites with a high percentage of iron.

Holocene:  The name of the current epoch that commenced with the termination of the Pleistocene. Together, the Holocene and Pleistocene comprise the Quaternary period. Human recorded history is entirely confined to the Holocene epoch, in spite of the fact that the presence of modern humans appears to have extended back into the Pleistocene at least 150,000 years. The term means ‘the whole of recent life.’

hoodoo:  An American term for a weirdly shaped pillar of solid rock in a semi-arid environment, similar in form to an earth pillar. Usually assumed to have been created by wind action.

hydrological cycle: A simplified model of the flow of water, ice, and water vapor from place to place. Water flows through the atmosphere, across the land, where it is also stored as ice, and within groundwater. Solar energy empowers the cycle. [Geosystems]

hydrology:  The scientific study of the distribution, circulation and properties of water in the atmosphere, at the Earth’s surface as well as below the Earth’s surface.   Palaeohydrology is the study of the actions and effects of ancient water flows that are no longer in operation. Study of catastrophic flooding encompasses palaeohydrology.

imbrication:  The tendency for water transported rocks to settle into inclined stacks, shingle fashion, or similar to a row of books which has inclined over on its side. The angle of tilt points up in the direction of current flow and can serve as an indicator of palaeocurrent direction.

interglacial:  During the Quaternary, a phase when glacial ice sheets retreated and the climate became more equable. We are presently in a climate that would be considered interglacial.

irons:  The class of meteorites composed primarily of iron, usually allowed with small amounts of nickel and cobalt.

isostacy:  The state of balance which the Earth’s crust tends to maintain. A condition of equilibrium, comparable to floating, of the units of the lithosphere above the asthenosphere. Isostatic compensation is the adjustment of the lithosphere to varying mass loadings such as occurs during the transition into or out of an Ice Age.

Jökulhlaup:  An Icelandic term for a glacial outburst flood. In Iceland the term usually refers to a flood caused by subglacial volcanism producing a reservoir of water that percolates under pressure to the glacier margin where it can discharge catastrophically. The term is finding its way into more general use to apply to any flood bursting out from a glacier as the result of the glacier acting as a dam causing the impoundment of a lake. As the lake deepens the pressure causes the failure of the glacial dam, hence the outburst flood. 

K -- P

kame:  A steep-sided, typically conical shaped hill, sometimes elongated into a ridge like structure, composed of sand and gravel originating when sediment collected in openings in stagnant glacial ice.

kame terrace:  A flat topped ridge or terrace feature occurring between a valley glacier and the valley slopes, formed by meltwater streams flowing laterally to the glacier, composed of drift and usually showing bedding structure. When the glacial ice melts away the material assumes the form of a flat topped bench along the flanks of the valley. It is also probable that nearly identical formations can result by large masses of flood sediment deposited over a valley floor being subsequently downcut by waning flood or post flood current flows.

Kansan:   The name given to the second of the four classical glacial stages of the Pleistocene. So named because early studies in North America focused on till deposits in the state of Kansas. It was preceded by an interglacial stage called the Yarmouthian and followed by an interglacial stage called the Aftonian. The equivalent stage in the Alps is called the Mindel.

kettle:  A depression in the surface of the ground caused by a block of ice or an iceberg being partially or completely buried in till or glacial drift and then melting away.

Kuiper belt:  A disk shaped reservoir of comets first theorized by Dutch-American astronomer Gerard Kuiper in 1951, assumed to occupy the region from about 40 to 100 AU (astronomical units) from the Sun lying near the plane of the ecliptic and to be comprised of material left over from the formation of the planets. Confirmation of this idea began in the 1990’s with repeated discoveries of 100 to 400 km (60 to 240 miles) diameter objects at heliocentric distances close to 40 AU. Most astronomers believe the Kuiper Belt is the source of the majority of short period comets.  

lacustrine: Applies to sediments deposited in a lake.

Laurentide ice sheet:  The greatest glacial mass of the Wisconsin Ice Age. It grew from centers near Hudson Bay and expanded outward radially from its core. It reached to the Arctic Ocean on the north, the Atlantic Ocean on the east, the foot of the Canadian Rockies on the west and southward into the regions of New England, the Great Lakes region into Ohio, and the prairies of the Dakotas and Montana, and south along the Mississippi Valley nearly to St. Louis. At its center over Hudson Bay the ice sheet was some 2 miles thick. At its maximum extent it covered some 5 million square miles. Together the Laurentide and Cordilleran Ice sheets buried most of Canada during the Wisconsin ice age maximum.

lithosphere: The rigid outer, rock layer of the Earth, what is generally thought of as the crust, but also including the upper part of the mantle, while excluding the hydrosphere and the biosphere. The thickness of the crust can vary from 5 to 40 km (3 to 25 miles)  in thickness, while the bottom of the lithosphere varies from about 50 to 100 km (30 to 60 miles) below the Earth’s surface.

Little Ice Age:

LL-chondrite:  The class of meteorites with the lowest amounts of metal and/or iron.
loess:  Deposits of assumed windblown silt, lacking visible layers, generally buff colored, and capable of maintaining a nearly vertical cliff. Generally homogenous in texture, weakly coherent and porous. Loess deposits blanket wide areas of the Mississippi Valley, eastern China, central Europe and Russia.  Usually Pleistocene, sometimes early Holocene in age. It has been suggested that it could be created when rainfall washes dust out of the air.

long period comet:  a comet with an orbital period greater than about 200 AU, although this distance is somewhat arbitrary. This class of comets have orbits described by the properties of a parabola, a member of the family of conic sections which does not close upon itself like an ellipse. Since most comets which have been catalogued have been observed since about the year 1800 AD there must exist many comets of this category which have not yet been identified. The count of long period comets whose orbits have been determined with reasonable accuracy , based upon both modern and ancient observations is 681 as of 1993.

mass extinction:  The sudden disappearance of a large fraction of life on Earth all at the same time.

mass wasting: a form of mass movement of unconsolidated material downslope by the action of gravity. The material involved in mass wasting can be rock, soil or regolith. The movement is usually triggered by over saturation of the material by rainfall, or by seismic activity.

Mesozoic:  A Greek term meaning ‘middle life’, it refers to the second of the geological eras, following the Palaeozoic and preceding the Cenozoic. It is subdivided into three periods known as the Triassic, Jurassic and Cretaceous. The evidence now points to the Mesozoic being terminated by a series of great catastrophes involving cosmic impact and large scale volcanism.

meteorite:  A solid body of extraterrestrial origin which successfully traverses Earth’s atmosphere to reach the surface. It is usually composed of nickel, iron and silicate minerals in varying proportions leading to different classifications of meteorites according to composition.

Missoula Flood:  The name most frequently used for the greatest known freshwater flood in geological history that occurred at the end of the Wisconsin Ice Age in the Pacific Northwest of the USA. However, the features that were at one time interpreted as the product of a single flood are now interpreted as resulting from multiple floods. The prevailing explanation for this flood or floods is that a large proglacial lake existed in the mountain valleys of western Montana in the watershed of the Clark Fork River, created when a lobe of the Cordilleran Ice sheet blocked the mouth of the Clark Fork in the present day region of Lank Pend Orielle, northern Idaho. According to the theory this glacial dam gave way releasing the impounded waters of Lake Missoula, which subsequently flowed west out over eastern Washington state, forming the Channeled Scabland. Important early studies of Lake Missoula and its relation to the Missoula Flood were undertaken by J.T. Pardee between 1910 and 1944. The first studies linking the Channeled Scabland to catastrophic megafloods were undertaken by J Harlan Bretz in the 1920’s.

monocline:  A stratigraphic flexure with two folds connecting relatively level strata at different elevations.

moraine:  An accumulation of heterogeneous rubbly material, including angular blocks of rock, boulders, pebbles and clay that has been transported and deposited by a glacier or ice sheet. This is typically the most commonly used term for glacier created landforms. First used by French peasants in reference to deposits near glacial margins in the French Alps. There are a number of classifications of moraine, depending upon its relationship to the glacier and its mode of deposition. End moraine is a ridge of till or drift formed at the terminus of alpine and continental glaciers. Ground moraine is the blanket of till laid down as a glacier recedes or melts away. The farthest limit of glacial advance is marked by the presence of terminal moraine where the ice margin may have stabilized for a period prior to its recession, building a prominent ridge conforming to the shape of the ice front. During pauses in its retreat the shrinking glacier creates recessional moraines. As a mountain glacier moves downvalley it excavates rock material from along side of the valley walls, which, upon disappearance of the ice forms lateral moraine. Where glaciers emanating from two converging valleys meet and coalesce the lateral moraines can join in the contact between the two glacial streams forming medial moraine. They show up as dark stripes within the ice.  [T&L]

Near Earth Object (NEO)  An asteroid or comet that can come within about 1.3 AU of the Earth. It is from the family of NEO’s that any potential Earth impactors are likely to originate.

Oort cloud:  A reservoir of comet nuclei orbiting between about 300 and 3000 AU from the Sun, although they could perhaps orbit at distances up to 100,000 AU, or close to half the distance to the nearest stars. The orbital period of comets in the cloud are on the order of several million years. The existence of this cloud was first theorized by Dutch astronomer Jan Oort in 1950. Estimates by astronomers analyzing the periodicities in the orbits of long and short period comets conclude that there could exist up to 7 trillion comets in the Oort cloud.

oriented lakes:  A term referring to a grouping of enclosed lake basins with parallel axial alignment. The origin of oriented lakes has been controversial. They have been attributed to selective glacial erosion in regions where glaciation was active; to deflation through predominant wind direction; to differential thawing of permafrost where they are found in Arctic regions and to subsurface karstic and/or solution processes. Two examples are the Oriented Lakes of the Alaskan Arctic coastal plain and some of the water filled basins of the so-called Carolina Bays in North and South Carolina. In the case of the Carolina Bays one of the early theories of formation attributed them to a large scale multiple meteorite strike, perhaps due to the break up of a large comet.

orogenesis:  The processes of mountain building resulting from the effect of forces acting tangential to the Earth’s crust which results in thrusting, folding and faulting, often associated with increased igneous activity. It appears that throughout Earth history there have been periods, or episodes of orogeny, rather than a process occurring uniformly through time.

paleoclimatology:  The study of past climates, mainly through the use of various fossils as well as a variety of proxies such as oxygen isotope ratios in ice cores, dendrochronology and so on.

periglacial:  Said of processes, conditions, areas, climates and topographic features at the immediate margins of glaciers and ice sheets, and influenced by the cold temperature of the ice. By extension, said of an environment in which frost action is an important factor, or of the phenomena induced by a climate beyond the periphery of the ice.

perihelion:  The point in the elliptical orbit of a planet or other revolving body such as a comet or asteroid at which it comes the closest to the sun.

periodic comets: or short period comets.  Comets whose elliptical orbits are well determined and have orbital periods generally less than about 200 years. The count of such comets observed through 1993 is 174.

Pleistocene:  An epoch of the Quaternary Period, coming after the Pliocene epoch. Characterized by the occurrence of glacial periods after the relatively mild climate of the Pliocene. It is the epoch during which humans arose. Generally it is assumed to have begun about 2 million years BP and to have terminated about 10,000 years BP with the transition out of the most recent, or Wisconsin, ice age. 

pluvial:  Pertaining to rain or to precipitation. Said of a climate characterized by high precipitation. Used to describe a geological feature or process resulting from rain.

punctuated equilibrium:  The hypothesis that evolution occurs during periods of rapid differentiation (often accompanying speciation), which are followed by long periods in which few if any characters evolve.  [Biogeography]

Q -- Z

Quaternary period:  The geological period comprising the Pleistocene and Holocene epochs.

radiant:  A point in the sky from which meteors, during a meteor shower, appear to emanate. The radial nature of a meteor shower is due to an illusion of perspective, wherein the flight paths of the separate meteoric bodies are actually parallel, they appear divergent similar to the manner in which a straight stretch of railroad tracks, or a highway with power poles, appear to diverge from a point in the distance as they approach the viewer. Meteor showers are named for the constellation nearest the radiant point of the shower, hence the Geminids are named for Gemini, from which constellation they appear to proceed, the Perseids from Perseus, the Leonids from Leo, and so on.  

refugium:  An area in which climate and vegetation type have remained relatively unchanged while areas surrounding it have changed markedly, and which has thus served as a refuge for species requiring the specific habitat it contains. [Biogeo]

resonance:  Gravitational perturbations on a body orbiting the Sun that are imparted by a third body whose orbital period is either a simple fraction of or multiple of  that of the other body. These perturbations can change the orbit of the body in question.

rhythmite:  Layered sediment associated with repeated backflooding into a tributary valley or channel by large floods passing through the main channel. The term was originally employed to name unique rhythmical layers exposed in the backwash areas of the Missoula Flood, for example the exposures at Burlingame ditch and along the Yakima River. Debate concerns the amount of time between deposition of successive layers.

Roche limit:  The boundary within which the gravitational forces of a planetary primary exceed the internal cohesion of an orbiting satellite body. Objects passing within the Roche limit will disaggregate to varying degrees depending upon their composition and density.  Astronomers witnessed an example of this effect in 1994 with the breaking up of Comet Shoemaker Levy 9 when it passed within the Jovian Roche limit.

roche moutonnées  Asymmetric bedrock bumps or hills with abraded up-ice or stoss faces and quarried down-ice lee faces. They can range in size from less than 1 meter to several hundred meters across, up to 50 meters high and up to a kilometer or more in length. They often have glacial striations etched into their surface. [Glaciers & Glaciation]

shattercones:  Rock structures, typically found in carbonate rocks such as limestone and dolomite, in which closely spaced fractures flare radially out and down from the apex of a cone. Shatter cones are found in closely spaced groupings with the collective apices pointing in the direction of the source of the shock wave. Shattercones are one of the diagnostic geologic features indicating intense shock due to hypervelocity impact.

shocked quartz:

Spaceguard  The proposed search program designed by NASA’s Near-Earth-Object Detection committee in 1992 to find all potentially dangerous objects in orbit about the Sun, that is, objects whose orbits cross that of the Earth.

stishovite:  Like coesite it is a high pressure polymorph of silica and an indicator of shock metamorphism, requiring pressures exceeding 100 kilobars.

strewnfield:  An area or region subjected to a multiple meteor fall, usually elliptical in shape, over which meteors, or fragments of meteors are found, presumably originating from the same parent body. 

stochastic:  Random, statistically expected, due to chance alone. Compare with deterministic.

stony-iron meteorites:  A class of meteorites containing both silicate and nickel-iron in equal proportion.

subglacial:  Formed or accumulated in the bottom parts of a glacier; said of meltwater streams, till, moraine, etc. Pertaining to the area immediately beneath a glacier.

submarine canyon:


taphonomy:  The study of the processes involved in transforming a newly deceased animal or plant into a fossil.

tektites:  Unusual stones composed primarily of silicate showing signs of having been molten which assume a variety of aerodynamic shapes indicating passage through the atmosphere. The most likely explanation for their origin is that they were molten droplets thrown out during formation of a hypervelocity impact crater. Several associations between impact crater and tektite fields have been demonstrated, for example the moldavites in Chechoslovakia, so called because they are found in the region of the Moldau River, having the same age of 14.5 million years as the nearby Ries Crater in Germany. Tektites can be spherical, tear-drop shaped, dumbbell shaped, cigar shaped, or even flying sauce shaped.

truncated spur:  A spur of land projecting into a periglacial valley that is subsequently truncated by the advance of a glacier into the valley, leaving a roughly triangular shaped, steep slope facing into the valley. Similar features are also produce by catastrophic floods as displayed repeatedly throughout the flow paths of the Missoula Flood.

tunnel valleys:  a conduit, or trench, cut by glacial meltwater at the base of the glacier near its margins. It generally extends from the margin of the ice sheet towards its interior. While active it can be partially recessed into the substrate and partly enclosed by the glacial ice itself. Many such valleys are hundreds of feet deep and are filled with nearly as many feet of sediment. Unlike normal river valleys that conform to a consistent gradient the floors of tunnel valleys can rise and fall in elevation. This implies that the water that eroded them was flowing under tremendous hydrostatic pressure.  In North America extensive tunnel valleys can be found in Minnesota, Wisconsin, Michigan, New York, Ontario and on the continental shelf off of Nova Scotia. In Europe large scale tunnel valley systems are found in Germany and Denmark. While varying widely in size they can be up to 100 km (60 miles) long and up to 4 km (2.5 miles) in width. The size of many tunnel valleys clearly imply catastrophic water flows, most likely associated with the meltdown and recession of the ice age glaciers. The presence of drumlins on the floors of some tunnel valleys reinforces the assumption of catastrophic water flows.

turbidite:  A sedimentary deposit found in marine or lacustrine environments which has settled out of turbid water flows. The sediments can vary widely in particle size from fine muds to sand, and generally display graded bedding.  A current carrying such sediments in suspension is denser than the surrounding water mass. This causes it to move relative to that water mass. A current of this type is called a turbidity current. Earthquakes, oceanic bolide impacts, volcanic eruptions, or anything that can impart a force of sufficient magnitude can initiate the movement. In marine environments the source of turbidity currents is usually associated with the continental slopes and shelves.  

till:  Unstratified drift, deposited directly by a glacier without reworking by meltwater, and consisting of a mixture of clay, sand, gravel and boulders ranging widely in size and shape. A tillite is a rock composed of such material.

underfit stream:  A stream that appears too small to have eroded the valley in which it flows. It is a common result of drainage changes effected by capture, by glaciers, or by climatic variations. [DOGT] It is also the result modern streams and rivers occupying valleys and canyons that have undergone large scale erosion and down cutting by catastrophic palaeoflooding.

Uniformitarianism:  The fundamental principle that geological processes and natural laws now operating to modify the earth’s crust have acted in much the same manner and with essentially the same intensity throughout geologic time, and that past geologic events can be explained by forces observable today; the classical concept that “the present is the key to the past”. The doctrine does not imply that all change is at a uniform rate, and does not exclude minor local catastrophes. Cf: catastrophism  [DOGT]

valley train:  A linear accumulation of glaciofluvial outwash following a valley for a considerable distance beyond the ice front. Most Pleistocene valley trains have been dissected by post-glacial fluvial erosion, leaving the remnants in the form of terraces. [DOPG]

varve:  A laminar sedimentary sequence usually deposited in a proglacial lake glacial meltwater. The laminations typically form a two layered couplet, with a lighter and thicker ‘summer’ layer below and a usually darker and thinner ‘winter’ layer above. In a uniform scenario one varve is deposited annually, which allows counting and correlation of varves for the development of chronologies.

water gap:  A deep pass in a mountain ridge, through which a stream flows; esp. a narrow gorge or ravine cut through resistant rocks by an antecedent stream. The Delaware Water Gap is a famous example.

whalebacks:  Eroded bedrock forms resembling the back of a whale. They are typically smooth, elongate, symmetrical features carved into bedrock by either glacial ice or subglacial meltwater, or both. Large whalebacks eroded in bedrock can be up to several thousand feet long. Whaleback forms can also occur in erratic boulders.

wind gap:  A valley or notch in a ridge through which no stream passes. Resembles a dry meltwater channel. The formation of a wind gap is generally attributed to river capture, in which the stream that formerly occupied the valley has been incorporated into another drainage system. A wind gap is usually higher in elevation than a water gap. A study of megaflood landscapes has revealed that some features created by catastrophic water flows crossing pre-flood divides are essentially identical to wind and water gaps.

Wisconsin Ice Age:  The last, or most recent of the four classical glacial stages of the North American Pleistocene. It follows an interglacial period called the Sangamon. Considered to have lasted about 60,000 years, beginning about 70 to 75,000 years BP and ending with the termination of the Pleistocene about 10,000 years BP. It is the final of the four classical glacial ages.


References used and sources consulted in compiling the
Glossary for Catastrophists

Dictionary of Geological Terms – 3rd Edition. Robert L. Bates & Julia Jackson, Editors. Prepared by the American Geological Institute.  [DOGT}

The Penguin Dictionary of Physical Geography – John Whittow (1984)  [DOPG]

The Earth: An Introduction to Physical Geology: Edward J. Tarbuck & Frederick K. Lutgens. 4th Edition (1992)  MacMillan Publishing Co.  [T&L]

Biogeography – 2nd edition. (1998) James H. Brown & Mark V. Lomolino  [Biogeo]

Glaciers & Glaciation – Douglas I. Benn & David J.A. Adams (1998) Arnold, London and John Wiley and Sons  [G&G]

American College Dictionary – Barnhart, C.L. (1968 ed.)  [ACD]

Geosystems – Robert W. Christopherson (2000) Prentice-Hall

Physical Geology – Sheldon Judson and Marvin E. Kauffman (1990) Prentice-Hall, Inc.

Rogue Asteroids and Doomsday Comets – Duncan Steel (1995) John Wiley & Sons, Inc.

Understanding the Universe – Phillip Flower (1990)  West Publishing Co.  [UTU]