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ASBOG FG
| Term | Definition |
|---|---|
| Law of Superposition | Younger layers of rocks sit atop older layers |
| Accuracy | How close a measurement conforms with a standard or accepted value |
| Apparent Dip | The inclination of a plate measured in a direction not perpendicular to strike |
| Apparent Dip Direction | The bearing of the vertical plane containing the apparent dip angle |
| Attitude | The orientation in space |
| B | The angle between strike and the apparent dip direction |
| Bearing | The horizontal angle between a line and a specified coordinate direction, usually north or south |
| Depth | The vertical distance from the ground surface downward to a feature of interest |
| Dip | The inclination of the line of greatest slope of an inclined plane measures perpendicular to strike |
| Directed Line | A line described by its bearing and plunge |
| Fold Line | A hinge line along which a vertical cross section may be constructed and then flattened out to a horizontal or map view |
| Inclination | A general term for the vertical angle between the horizontal and a plane or line, measured downward |
| Outcrop Width | The width of an outcrop, as measured on a map view, perpendicular to strike |
| Pole | A line perpendicular to a plane, and represented as a point on a stereographic projection |
| Plunge | The vertical angle between a line and a horizontal |
| Precision | The degree of agreement of consistency of repeated measurements |
| Projection | The process by which points on one surface are transferred to another surface, such that in each view (map or cross section) the points correspond |
| Rake (Pitch) | The angle measured in a specified plane, between a line and the horizontal |
| Slope Angle | The angle from the horizontal down to the slope. |
| Stereonet | A representation of angular relationships between planes and lines. In structural geology, a stereonet is synonymous with Wulff net, an equal angle stereographic projection. |
| Strike | The bearing of a horizontal line in an inclined plane |
| Thickness | The perpendicular distance between the top and bottom of a geologic unit. |
| Trend | The bearing of the vertical plane containing a line |
| Blind Thrust | A thrust fault that does not reach the ground surface |
| Detachment Fault | A low-angle normal fault associated with regional extension |
| Dip-slip Fault | A fault in which the movement is parallel to the dip of the fault plane, such as a normal, reverse, or listric fault |
| Fenster | A "window" into rocks underlying a thrust fault |
| Footwall Block | The block that underlies a non-vertical fault |
| Ga | Abbreviation for Giga-annum; one billion years |
| GIS | Abbreviation for Geographic Information System, a computer-based tool used for mapping, analyzing, and visualizing geographically referenced data |
| GPS | Abbreviation for Global Positioning System, a radio navigation system that determines the exact location, time, and velocity (from triangulation) |
| Growth Fault | A fault that forms contemporaneously with deposition in sedimentary rock. The throw increases with depth and the sedimentary units on the downtown side are thicker than the corresponding units on the up |
| Hanging-wall Block | The Block that overlies a non-vertical fault |
| Heave | The amount of horizontal displacement on a fault |
| Ka | Abbreviation for Kilo-annum; one thousand years |
| Klippe | An outlier of a thrust sheet completely surrounded by the exposed footwall |
| Key Beds | A well-defined, easily identified strata that is distinctive enough to be useful in correlation in mapping |
| Listric Fault | A fault with curved fault plane. Near the surface the fault plane is steeply dipping, but it becomes progressively flatter with depth. Listric faults may be normal or reverse |
| Ma | Abbreviation for Mega annum; one million years |
| Magnetic Declination | The angle between true North and magnetic North |
| Nappe | A sheetline rock unit that has moved over other rocks (allochthonous) on a predominantly horizontal surface |
| Net Slip | The distance between two formerly adjacent points on either side of the fault, measured on the fault surface |
| Nonconformity | An unconformity formed by older igneous rocks in contact with younger sediments, indicating a missing time after the igneous intrusion |
| Normal Fault | A dip-slip fault in which the hanging wall has moved down relative to the footwall. The dip of the fault is between 45 degrees and 90 degrees |
| Oblique-slip Fault | A fault in which movement is not parallel to the strike or dip of the fault plane |
| Offset | The horizontal component of displacement measured perpendicular to the strike of the disrupted unit |
| Reverse Fault | A dip-slip fault in which the hanging wall has moved up relative to the footwall. The dip of the fault is between 45 and 90 degrees. |
| Rule of V's | The outcrop pattern of a formation as it crosses a valley forms a V shape (as viewed on a map). The V points in the direction that the formation underlies the valley |
| State Plane Coordinate System | A two dimensional coordinate system developed by the National Geodetic Survey for use in states and counties |
| Strike Separation | The horizontal distance between a stratigraphic unit offset by a fault, measured along the strike of the fault. It is an apparent displacement |
| Strike-slip Fault | A fault in which movement is parallel to the strike of the fault plane |
| Throw | The amount of vertical displacement on a fault, also, the vertical component of the slip |
| Thrust Fault | A reverse fault in which the fault plane dips less than 45 degrees |
| Unconformity | A gap in the geologic record; an interruption in the depositional sequence that implies uplift and erosion have removed part of the geologic record or non-deposition has occurred |
| Karst | topography of a region underlain by limestone, dolomite, gypsum, or other rocks affected by dissolution. Characterized by surface depressions in which water is intercepted and diverted into underground caverns and passageways. |
| Four necessary conditions for development of karst terrain | 1. A soluble rock, preferably limestone, at or near the surface 2. a dense rock, highly jointed and thin-bedded 3. Entrenched valleys below uplands underlain by soluble and well-jointed rocks 4. A region of moderate to abundant rainfall |
| Terra rossa | A red clayey soil found mantling the ground surface and extending into joints or fractures resulting from surface or near surface solution, usually found on moderate to gentle slopes |
| Lapies | Grooved or fluted surface resulting from the solution of limestone at or near the surface in an area of high relief. The grooves range in width from a few millimeters to more than a meter in width and commonly result in knifelike ridges |
| Sinkholes | A circular depression that is commonly funnel-shaped and can be a few feet to a hundred feet in diameter. This is the most commonly observed feature of karst terrain. |
| Sinkhole ponds or karst lakes | a pond or lake resulting from the clogging by clay of a doline sinkhole that perches water above the water table |
| Swallow holes | a hole in the bottom of a sinkhole which allows surface water runoff or streams to flow into the subsurface cavities |
| Karst window | A hole in the ground which one can observe an underground stream flowing from one cavern to another. A hole in a cavern which breaks the surface |
| Uvala | An elongated karst window that has occurred by the collapse of an extensive portion of a subsurface waterway. These features can extend 1000 ft to a mile or more |
| Polje | A sinkhole formed by solutional modification of the rock (similarly to a doline) in a previously faulted or folded structure. This feature can be 30 miles or more in length |
| Solution-subsidence trough | a non-tectonic feature , up to 10 miles in length, resulting from concurrent subsidence and solution along joints or faults |
| Sinkhole or karst plain | a limestone plain exhibiting sieve-like characteristics resulting from numerous sinkholes intercepting any surface water and diverting them to subsurface channels |
| Sinking creeks | any surface creek or stream which disappears underground in kart terrain; many disappear in a swallow hole |
| Sink | the point at which a sinking creek ends, often in an observable swallow hole |
| Blind valley | a valley that ends at a swallow hole due to a prolonged period of upstream erosion above the sinkhole |
| Solution valley or karst valley | a transitional feature between surface ans subsurface drainage in an area of clastic rocks. A special type of blind valley |
| Natural tunnels and bridges | Features produced by the underground flow of water in karst terrain. When the tunnel sections collapse leaving only small segments, bridges are formed |
| Hum | isolated hill remnants due to erosion by solution in karst terrain |
| Cavern | large caves that may extend in any direction, have one or several levels, and are created by solution of limestone along joints and bedding planes |
| Travertine | A deposit of calcium carbonate precipitate that can be found in limestone caverns coating the cavern walls, floors, and ceilings |
| Dripstone | the travertine deposits that result from the calcium carbonate-rich water dripping from the ceiling of a cave or cavern. Stalactites are downward/stalacmites are upward protrusion |
| Helictite | An irregular twiglike deposit forms in a cavern where there is not enough water to form drips but the surface remains damp or the water comes from a tiny hole or tube within the deposit and the water flows out the end |
| Ice-scoured plain | an assemblage of erosional landforms on exposed bedrock resulting from the flow of an ice cap. Exhibits many of the same surficial features that are found in the areas of alpine glaciation such as striations, grooves, and polished surfaces |
| Roche moutonnee | An elongated bedrock knob which is oriented parallel to the direction of glacial flow and has a smooth rounded upstream end and usually a steep rough downstream end where the glacier plucked out the rock as it moved away. |
| Streamlined topography (mammillated surface) | a series of smooth rounded erosional rock mounds alternating with parallel valleys resulting from the smoothing off of a mountainous region by the ice cap |
| Arcuate terminal moraine | arcuate moraine that has been deposited at the terminus of the glacier, marking the furthest progression of the glaciation. |
| Till plain | also called ground moraine, deposition by an ice cap of glacial till forming a relatively flat to undulating surface which covers an extensive area and buries the preglacial topography |
| Drift | refers to all rock and associated material that has been carried by and deposited by a glacier, glacial ice, or water running from a glacier. |
| Till | an unsorted, unstratified glacial deposit composed of a heterogeneous mixture of clay, silt, sand, gravel, and boulders. usually unconsolidated and deposited directly by a glacier without having been reworked by meltwater |
| Ground moraine | often used interchangeably with till plane. can be composed of both the material contained within the glacier as well as that being moved along at its base |
| End moraine | the end moraines found at the maximum extent of a continental glaciation are similar to those found in alpine glaciation though they tend to be much more extensive and often have less steep slopes, occasionally making it difficult to distinguish |
| swell & swale topography | till deposits rich in clay may result in a gently undulating surface which often is also found in areas that have had multiple glaciations |
| drumlin | an elongated ellipsoidal feature which can be composed of a wide variety of till materials ranging from clays to relatively large rock fragments; some even have a bedrock core. |
| outwash plain | a broad plain composed of outwash; stratified debris that is carried by meltwater streams both in front of and beyond the terminal or end moraine. typically composed of coarser grained materials close to terminus grading to finer with distance |
| Esker | these serpentine shaped deposits develop as the load carried by the streams flowing beneath, within, and above the glacier, once it has become stagnant, is dropped. stratified, appearance of inverted stream channels oft with branching |
| Kettle | a depression in the postglacial terrain formed by the melting of a large stagnant ice block which allows for the settlement of the overlying glacial drift. in some areas the outwash plains are pitted with many kettles. |
| Kame & kame terrace | small hummock or terrace of ice-contact drift that has resulted from the deposition of sediment either in crevasses at the surface of the glacier, on the irregular surface of stagnant glaciers, or from streams flowing at the edge of glaciers |
| cirque | a horseshoe-shaped hollow high on a mountainside that was created by the erosive action at the head of a glacier |
| tarn | a small deep lake formed in a cirque basin |
| glacial polish | a smooth surface produced on bedrock by abrasion by the movement of a glacier |
| striations | lines scraped into the bedrock by rocks being carried along at the base of the glacier. Striations generally indicate the direction of glacier movement, larger rocks create grooves or grooved rock that can be as big as a valley |
| glacial trough (U shaped valley) | a steep-sided valley that extends down from the cirque in which glacial action has widened and deepened an existing valley |
| glacial steps or stairway | a series of cross valley steps extending down from the cirque, these steps are characterized by a relatively flat floor or with a slight upvalley slope broken by steeper sections stepping down valley |
| paternoster lakes | a series or chain of lakes occupying the glacial steps |
| hanging valley | a U-shaped glacial tributary valley truncated by a deeper U shaped glacial main valley leaving a valley whose mouth is relatively high on the main valley wall. the discordance is due to the greater erosive power of the main glacier |
| Arete | a jagged sharp sawtooth-like ridge that results from the growth of cirques on opposite sides of a mountain ridge by alpine glaciation |
| Col | a narrow sharp-edged pass or sag between cirque head and side walls along an erete |
| Horn | a jagged sharp peak at the high point in an arete which has been sculpted by the erosional action of three or more cirques. This pyramidal feature is the remainder of the original mountain summit in a region modified by alpine glaciation |
| Monuments (tinds) | a horn that has been isolated by the lateral intersection of cirques |
| Truncated or faceted spur | a ridge, which once protruded into a pre-glacial valley, that has been truncated by the abrasion of glacial action as it straightened the valley. This feature characteristically has an inverted V-shaped face |
| Fjords, fiards (fjards) | a submerged glacial trough or valley at its seaward end resulting from the raising of sea level as the glaciers melted. The fiard is a shallower and shorter, but often broader, feature than the fjord. |
| Trough lakes | similar to fjords in that they consist of a long glacial trough and contain water but are found above sea level |
| Moraine | a mound or ridge composed of accumulated glacial drift or till deposited directly by the glacier. Moraines are composed of a heterogeneous collection of unsorted and unstratified clay, sand, silt, gravel, and boulders. |
| End (terminal) moraine | similar to that found in continental glaciation |
| Lateral mortaine | a linear moraine located along the edge of a valley glacier and composed of materials deposited on the glacier from the valley walls |
| Medial moraine | a linear moraine paralleling the valley walls which occurs where two valley glaciers merge joining the two inside lateral moraines from the two or more tributaries as they flow into the more major drainage |
| valley train | a long narrow deposit out outwash (sand and gravel), deposited by glacial meltwater, which begins at the end moraine and extends downvalley |
| Lacustrine plains | a plain that has formed by the filling of a lake with lake sediments and alluvium which has been deposited along the margin of the glacier. Characterized by very flat valley bottoms in hilly terrain |
| knob & basin topography | also called knob-and-kettle topography, a hummocky landscape consisting of knolls or mounds of glacial drift in an area also interspersed with basins or kettles. the basins often contain water |
| yardang | a long, jagged, sharp-edged ridge between troughs, oriented with the direction of the prevailing winds in an arid region which is underlain by relatively weak materials. |
| ventifacts | stones that have been abraded by the wind on at least one side so they are polished or faceted. they are usually only found in a unique environment of no vegetation, strong wind and plentiful sand |
| pedestal rocks | commonly called balanced rocks, these formations are the result of a combination of wind and water erosion (deflation) in an area where there are resistant rocks capping weaker more easily eroded rocks |
| blowout | a depression caused by deflation in an area where either migrating dunes exist or a small break develops in the surficial integrity of a stabilized windblown deposit or in some cases the underlying material is composed of a poorly to non-indurated materia |
| desert pavement | sometimes called desert armor, name applied to the relatively flat residual surface of closely-packed wind-polished stones. Result of removal of fine-grained particles by wind and sheetwash. often remaining stones somewhat cemented in place |
| ripples and ridges | small-scale features that are usually found on the surfaces of sand deposits resulting from the flow of wind or water over the surface. the shape of the ripple mark can be an indicator of direction of flow in depositional environment |
| sand shadows & sand drifts | these two features are similar in that both form as a result of an obstruction in the path of migrating sands. The sand shadow forms behind the obstruction where the velocity of the wind declines causing the sand to drop. |
| Dunes | sand that is piled up as a result of transportation by the wind of sand-sized particles. Often found in back beach areas of desert climates where the topography is relatively flat and the surface sand is dry. Most dunes are composed of a well-sorted sand |
| barchan dune | crescent-shaped, tails to leeward, rarely vegetated |
| parabolic dune | crescent-shaped, tails to windward, often associated with some vegetative cover |
| transverse dune | perpendicular to the wind, exhibits the traditional gentle windward slope and the steep slip face nearing the angle of repose. Both the Barchan and Parabolic dunes are a variety of transverse dune |
| longitudinal dune (seif) | parallel to the wind, through to develop in areas in which the prevailing wind causes the dunes to lengthen in the direction of the wind but the dune height increases due to the cross winds during periods of irregular wind flow. |
| whaleback or sand levees | a very large hill or ridge of sand elongated parallel to the prevailing wind. in general whalebacks to not mirgate and can be over 100 miles long, a couple of miles wide and 150 feet high |
| undulations | similar to a whaleback but much smaller |
| sandsheets | extensive flat areas covered with a coarse grained sand that does not form dunes, but typically are covered with ripple marks |
| loess | wind-blown silt that is calcareous, homogeous, and permable. loess covers extensive areas in the pacific northwest and mississippi valley regions |
| sheet flow (sheet wash) | unconcentrated overland flow |
| base level | the lowest level beyond which a stream cannot erode its bed |
| bedload | heavier particles (bounders, pebbles, gravel and sand) which travel along the bottom of a channel by bouncing (saltation) or traction which are not carried continuously in the water column |
| alluvial fans (cones) | develop when the stream gradient becomes too flat as it exist the hills and the water becomes too slow to carry the sediment load, which is deposited at the exit from the hills where the stream intersects the lowland valley bottom. |
| deltas | when streams enter lakes or seas the flow branches out and sedimentation takes place because of the change in gradient. coarser grains settle quickly into foreset beds sloping offshore |
| gravel bars (sand bars) (point bars) | can develop midstream when the flow velocity of the water declines where it borders with a higher velocity flow in the stream. bars are usually linear in flow direction. often relatively well sorted or poorly graded deposits. |
| natural levees | form when flood stage has been reached as the river recedes. the water velocity declines dropping some of the sediment load parallel to the shore. the river moves more towards mid channel as the water drops making the levee higher toward the main channel |
| braided streams | inchannel deposition of sands and gravels in a braided pattern is due to changes in the velocity of the water within the channel. Increased erosion overloads the streams capacity to carry the bedload. |
| stream terraces | in profile stream terraces are bounded uphill by the hillside slope and downhill by the eroded stream channel. terraces are the eroded remnants of either the old valley floor, in the case of rock terraces having a rock base, or depositional accumulation |
| meander loops | 2 types. free meanders form in valley bottoms on flat flood plains and can change course by eroding river banks and depositing material. incised meanders form on initially flat surfaces but flow increases or the underlying materials are soft and erode |
| ripple marks | there are two types of ripple marks. asymmetrical ripple marks indicate directional current. the symmetrical ripple marks are indicative of oscillating water. |
| peneplains | broad, relatively flat to gently undulating surfaces that are created as a result of variety of erosional processes acting over a long period of time, including marine abrasion or sheet wash |
| pediments | slightly inclined planar surfaces. meet the mountains generally at an abrupt angle on the upper part of the slope and grade into the valley bottom. frequently rock floored or with a thin veneer of alluvium. often found in arid regions |
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