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* Also called bidirectional ripples, or symmetrical ripple marks have a symmetrical, almost sinusoidal profile; they indicate an environment with weak currents where water motion is dominated by wave oscillations.
* In most present-day streams, ripples will not form in sediment larger than coarse sand. Therefore, the stream beds of sand-bed streams are dominated by current ripples, while gravel-bed streams do not contain bedforms. The internal structure of ripples is a base of fine sand with coarse grains deposited on top since the size distribution of sand grains correlates to the size of the ripples. This occurs because the fine grains continue to move while the coarse grains accumulate and provide a protective barrier.
;Crest: The point on a wave with the maximum value or height. It is the location at the peak of the wave cycle as shown in picture to the right.
;Trough: The opposite of a crest, so the minimum value or height in a wave. It is the location at the very lowest point of a wave cycle also shown in picture to right.
;Lee: The lee side has a steeper slope than the stoss. The lee is always on the back side of the ripple, which is also on the opposite side of where the current flow meets the ripple. The current flows down the lee side.
;Stoss: The stoss is the side of a wave or ripple that has a gentle slope versus a steeper slope. Current always flows up the stoss side and down the lee side. This can be used to determine current flow during the time of ripple formation.
File:Dakota ripples.jpg, Ripple marks in
Ripple Marks and Uniformitarianism
Unidirectional flow: Sand ripples and grain distribution 2D model
Unidirectional flow: Sand ripples and topography 2D model
Waves: Sand ripples and grain distribution 2D model
Waves: Sand ripples and topography 2D model
{{Authority control Sedimentary structures Patterned grounds
In geology
Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...
, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
( current or waves) or wind.
Defining ripple cross-laminae and asymmetric ripples
* ''Current ripple marks'', ''unidirectional ripples'', or ''asymmetrical ripple marks'' are asymmetrical in profile, with a gentle up-current slope and a steeper down-current slope. The down-current slope is the angle of repose, which depends on the shape of the sediment. These commonly form in fluvial andaeolian
Aeolian commonly refers to things related to either of two Greek mythological figures:
* Aeolus (son of Hippotes), ruler of the winds
* Aeolus (son of Hellen), son of Hellen and eponym of the Aeolians
* Aeolians, an ancient Greek tribe thought to ...
depositional environments, and are a signifier of the lower part of the Lower Flow Regime.
* Ripple cross-laminae forms when deposition takes place during migration of current or wave ripples. A series of cross-laminae are produced by superimposing migrating ripples. The ripples form lateral to one another, such that the crests of vertically succeeding laminae are out of phase and appear to be advancing upslope. This process results in cross-bedded units that have the general appearance of waves in outcrop sections cut normal to the wave ''crests''. In sections with other orientations, the laminae may appear horizontal or ''trough''-shaped, depending upon the orientation and the shape of the ripples. Ripple cross-laminae will always have a steeper dip downstream, and will always be perpendicular to paleoflow meaning the orientation of the ripples will be in a direction that is ninety degrees to the direction that current if flowing.Boggs Jr., Sam. (2006) Principles of Sedimentology and Stratigraphy, 4th ed. Scientists suggest current drag, or the slowing of current velocity, during deposition is responsible for ripple cross-laminae.Potter, Pettijohn. (1977) Paleocurrents and Basin Analysis
Ripple marks in different environments
Wave-formed ripples
* Also called bidirectional ripples, or symmetrical ripple marks have a symmetrical, almost sinusoidal profile; they indicate an environment with weak currents where water motion is dominated by wave oscillations.
* In most present-day streams, ripples will not form in sediment larger than coarse sand. Therefore, the stream beds of sand-bed streams are dominated by current ripples, while gravel-bed streams do not contain bedforms. The internal structure of ripples is a base of fine sand with coarse grains deposited on top since the size distribution of sand grains correlates to the size of the ripples. This occurs because the fine grains continue to move while the coarse grains accumulate and provide a protective barrier.
Ripple marks formed by aeolian processes
;Normal ripples: Also known as impact ripples, these occur in the lower part of the lower flow regime sands with grain sizes between 0.3-2.5 mm and normal ripples form wavelengths of 7-14 cm. Normal ripples have straight or slightly sinuous crests approximately transverse to the direction of the wind. ;Megaripples: These occur in the upper part of the lower flow regime where sand with bimodal particle size distribution forms unusually long wavelength of 1-25 m where the wind is not strong enough to move the larger particles but strong enough to move the smaller grains by saltation. ;Transverse aeolian ridges: There is some thought that transverse aeolian ridges are a form of fossilized ripple, but there is no conclusive evidence so far. ;Fluid drag ripples: Also known as aerodynamic ripples, these are formed with fine, well-sorted grain particles accompanied by high velocity winds which result in long, flat ripples. The flat ripples are formed by long saltation paths taken by grains in suspension and grains on the ground surface.Definitions
;Crest: The point on a wave with the maximum value or height. It is the location at the peak of the wave cycle as shown in picture to the right.
;Trough: The opposite of a crest, so the minimum value or height in a wave. It is the location at the very lowest point of a wave cycle also shown in picture to right.
;Lee: The lee side has a steeper slope than the stoss. The lee is always on the back side of the ripple, which is also on the opposite side of where the current flow meets the ripple. The current flows down the lee side.
;Stoss: The stoss is the side of a wave or ripple that has a gentle slope versus a steeper slope. Current always flows up the stoss side and down the lee side. This can be used to determine current flow during the time of ripple formation.
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
Dakota Formation, east side of Dinosaur Ridge. Scale bar on notebook is 10 cm.
File:Wren's Nest National Nature Reserve - ripple beds.jpg, Ripple beds in the Wren's Nest National Nature Reserve, Dudley, England
File:WaveRipple.JPG, Wave/symmetrical ripple, Nomgon, Mongolia
File:Climbing ripples.JPG, Cross-section through asymmetric climbing ripples, seen in the Zanskar Gorge, Ladakh
Ladakh () is a region administered by India as a union territory which constitutes a part of the larger Kashmir region and has been the subject of dispute between India, Pakistan, and China since 1947. (subscription required) Quote: "Jammu a ...
, NW Indian Himalaya. Ripples climb when sediment fluxes in the flow are very high.
File:Complex ripples.jpg, Complex ripple marks on Cambrian
The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...
tidal flat at Blackberry Hill, Wisconsin.
See also
* Capillary wave * Giant current ripples * Hertha Ayrton - pioneer in description of how ripples formed * Water on Mars - sedimentary ripple marks show indirect evidence of ancient water flows on our neighbor planet * Transverse aeolian ridges - mysterious fossilized features on Mars that resemble giant ripples * Washboarding - ripples on dirt roads formed by the interaction of vehicle wheels with the gravel and sedimentReferences
* Easterbrook, Don J. Surface processes and landforms. Upper Saddle River, N.J: Prentice Hall, 1999. Print. pp. 479-480. * Greeley, Ronald, and James D. Iversen. Wind as a Geological Process On Earth, Mars, Venus and Titan (Cambridge Planetary Science Old). New York: Cambridge UP, 1987. pp. 153-154 * Monroe, James S., and Reed Wicander. The Changing Earth: Exploring Geology and Evolution, 2nd ed. Belmont: West Publishing Company, 1997. pp. 114-15, 352.External links
Ripple Marks and Uniformitarianism
Unidirectional flow: Sand ripples and grain distribution 2D model
Unidirectional flow: Sand ripples and topography 2D model
Waves: Sand ripples and grain distribution 2D model
Waves: Sand ripples and topography 2D model
{{Authority control Sedimentary structures Patterned grounds