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Knickpoint

In geomorphology, a knickpoint or nickpoint is part of a river or channel where there is a sharp change in channel bed slope, such as a waterfall or lake. Knickpoints reflect different conditions and processes on the river, often caused by previous erosion due to glaciation or variance in lithology. In the cycle of erosion model, knickpoints advance one cycle upstream, or inland, replacing an older cycle.[1] A knickpoint that occurs at the head (furthest upstream extent) of a channel is called a headcut.[2] Headcuts resulting in headward erosion are hallmarks of unstable expanding drainage features such as actively eroding gullies.[3]

The Horseshoe Falls, one of the three Niagara Falls. The falls are a knickpoint, formed by slower erosion above the falls than below.

Knickpoints also occur on other planetary bodies that previously had or currently have surface liquids, namely Mars[4] and Titan.[5] On Mars, the knickpoints have a common elevation that suggest a common sea level for a former Martian ocean.[4] On Titan, mountain valleys adjacent to the present-day hydrocarbon seas show evidence of knickpoints and recent sea-level change.[5]

Formation edit

Knickpoints are formed by the influence of tectonics, climate history, and/or lithology.[6] For example, uplift along a fault over which a river is flowing will often result in an unusually steep reach along a channel, known as a knickzone. Glaciation resulting in a hanging valley are often prime spots for knickpoints. If lithology of the rock varies, such as shale amongst igneous rock, erosion will occur more steadily in the softer rock than the surrounding, tougher rock.

Base level is the elevation of the surface of the water body into which a river ultimately drains, usually the ocean. A drop in base level causes a response by the river system to carve into the landscape. This incision begins at the formation of a knickpoint, and its upstream migration depends heavily upon the drainage area (and so the discharge of the river), material through which it cuts, and how large the drop in base level was.[7]

Modern examples edit

 
In this satellite image of Victoria Falls, the gorges below the falls as well as developing crevasses below the surface of the river are visible. As the knickpoint recedes upstream, these crevasses will become, in turn, the location of the Falls.

Knickpoints include both waterfalls and some lakes. These features are common in rivers with a sufficient slope, i.e. enough change in elevation above sea level over their length to encourage degradation.

Influenced by lithology edit

Variations in stability of the underlying rock influence development of a bedrock-channeled river, as the waters erode different rock types at different rates. Victoria Falls, on the Zambezi River, is a spectacular example of this. The gorges visible by satellite imagery illustrate the erosional processes behind the formation of the falls. Here, much of the surface rock is a massive basalt sill, with large cracks filled with easily weathered sandstone made visible by the Zambezi's course across the land. The gorges downstream of the falls through which it flows were eroded over time by the action of the water.

Influenced by tectonic activity edit

Throughout New Zealand, tectonic uplift and faulting are actively contributing to knickpoint initiation and recession. The Waipoua River system, on the North island, has been studied and used to create mathematical models to predict the behavior of knickpoints.[8] The study showed a direct correlation between upstream drainage area and rate of migration, producing modeled data closely approximating the collected data. The Waipoua River system incises through sediments, for the most part, as opposed to bedrock.

Influenced by glacial activity edit

 
Bridalveil Fall, in Yosemite, flows over the edge of a glacially-carved hanging valley.

Sharp changes in slope are common in rivers flowing through the heavily carved landscape left behind when glaciers retreat. Glacial valleys, as well as isostatic rebound resulting from the removal of the mass of glacial ice contribute to this.

Niagara Falls, on the border of the United States and Canada, is a characteristic example of knickpoint. The falls have slowed in migration from approximately 1m per year as of 1900 to their modern 10 cm per year.[9] The falls, particularly Horseshoe Falls, are dramatically steep and caused by glaciation. The Great Lakes themselves lie in the depressions left behind by glaciers, as the crust is still rebounding.

Bridalveil Fall, in Yosemite Valley, California, pours over the lip of a hanging valley.

Paleomorphology edit

 
Dry Falls, Washington: a prehistoric knickpoint

Evidence of a knickpoint in the geologic past can be preserved in the shape of the bedrock below any subsequent depositions, as well as within sedimentary depositions left unchanged by human or other activity. Lakes characteristically fill in with sediment over time, but waterfalls often erode away. There are few obvious, dry examples still visible today of prehistoric knickpoints.

Evidence of massive prehistoric flooding edit

Dry Falls, a 3.5 mi long precipice in central Washington, is an example of an ancient knickpoint. Geologic evidence strongly suggests that the water which formed this feature flowed over the Channeled Scablands, bursting from the glacial lake Missoula during an event known as the Missoula Floods and into the Columbia River Gorge.

Evidence within karst topography edit

On the Upper Cumberland River, Tennessee, there exist a series of hydrologically abandoned caves which still hold river-deposited sediments. These caves were the subject of an effort to measure the rate of knickpoint migration along the river, as well as to approximate the discharge of the river over time.[10] In karst topography, a river dropping in level influences more than just its channel; as there is no longer water flowing at a certain level, caves and water tables will drop locally to the new level.

Evidence of large-scale base level drop edit

Large drainages into the oceans the world over can be seen to have continued over land which was once exposed, whether due to tectonic subsidence, sea level rise, or other factors. Bathymetric imagery is available for much of the United States' western coast, and in particular the ocean floor just offshore of rivers in the Pacific Northwest exhibit such underwater features.

In certain locations there are still knickpoints preserved in these drowned river channels and valleys. A study conducted within the Mediterranean basin[7] focused on such features. Here, incision was caused by the closing of the Mediterranean at the end of the Miocene. This sudden lack of ocean water influx allowed the basin to decrease in volume and increase in salinity, and as a result of the drop in surface level many of the rivers which flow still today into the Mediterranean began to incise.[7]

Movement edit

As is observed for many major waterfalls, knickpoints migrate upstream due to bedrock erosion[11] leaving in their wake deep channels and abandoned floodplains, which then become terraces. Knickpoint retreat is easily demonstrated in some locations affected by postglacial isostatic response and relative sea-level drop such as in Scotland. In other areas, dating of exposed bedrock terraces is more consistent with spatially uniform incision and persistence of the knickzone at about the same location.

A river, having gained or lost potential energy with its changed slope, will then proceed to work the knickpoints out of its system by either erosion (in the case of waterfalls; gained potential energy) or deposition (in the case of lakes; lost potential energy) in order for the river to reattain its smooth concave graded profile.

The rates of knickpoint migration, in the case of waterfalls, generally range between 1mm and 10 cm per year, with some exceptional values.[7]

Mathematical modeling edit

Knickpoint propagation is typically modelled with the semi empirical stream power law where the drainage basin size is used as a proxy for discharge, which in turn has a positive nonlinear correlation to the rate of knickpoint migration. Both analytical [12] and numerical solutions [13] have been proposed to solve the stream power law.

Automated extraction in GIS edit

Knickpoints and knickzones can be semiautomatically extracted from Digital Elevation Models in Geographic Information System software (i.e. ArcGIS). The problem with most of existing methods is that they are frequently subjective and require time-consuming data processing. A solution for these problems is a tool designed for ArcGIS, called Knickzone Extraction Tool (KET) which vastly automates the extraction process.[14]

See also edit

References edit

  1. ^ Tinkler, Keith J. (2004). "Knickpoint". In Goudie, A.S. (ed.). Encyclopedia of Geomorphology. pp. 595–596.
  2. ^ Bierman, Paul; Montgomery, David (2013). Key Concepts in Geomorphology.
  3. ^ Knighton, David (1998). Fluvial Forms and Processes, A New Perspective.
  4. ^ a b Duran, Sergio; Coulthard, Tom J.; Baynes, Edwin R. C. (2019-10-22). "Knickpoints in Martian channels indicate past ocean levels". Scientific Reports. 9 (1): 15153. Bibcode:2019NatSR...915153D. doi:10.1038/s41598-019-51574-2. ISSN 2045-2322. PMC 6805925. PMID 31641171.
  5. ^ a b Lucas, Antoine; Aharonson, Oded; Deledalle, Charles; Hayes, Alexander G.; Kirk, Randolph; Howington‐Kraus, Elpitha (2014). "Insights into Titan's geology and hydrology based on enhanced image processing of Cassini RADAR data". Journal of Geophysical Research: Planets. 119 (10): 2149–2166. Bibcode:2014JGRE..119.2149L. doi:10.1002/2013JE004584. ISSN 2169-9100.
  6. ^ Paul R. Bierman, David R. Montgomery. Key Concepts in Geomorphology, Freeman, 2013 ISBN 978-1429238601
  7. ^ a b c d Loget, Nicolas; Van Den Driessche, Jean (2009-05-15). "Wave train model for knickpoint migration". Geomorphology. 106 (3–4): 376–382. Bibcode:2009Geomo.106..376L. doi:10.1016/j.geomorph.2008.10.017.
  8. ^ Crosby, Benjamin T.; Whipple, Kelin X. (2006-12-06). "Knickpoint initiation and distribution within fluvial networks: 236 waterfalls in the Waipaoa River, North Island, New Zealand". Geomorphology. The Hydrology and Geomorphology of Bedrock Rivers. 82 (1–2): 16–38. Bibcode:2006Geomo..82...16C. doi:10.1016/j.geomorph.2005.08.023.
  9. ^ Hayakawa, Yuichi S.; Matsukura, Yukinori (2009-09-15). "Factors influencing the recession rate of Niagara Falls since the 19th century". Geomorphology. 110 (3–4): 212–216. Bibcode:2009Geomo.110..212H. doi:10.1016/j.geomorph.2009.04.011. hdl:2241/103715.
  10. ^ Anthony, Darlene M.; Granger, Darryl E. (2007-09-20). "An empirical stream power formulation for knickpoint retreat in Appalachian Plateau fluviokarst". Journal of Hydrology. 343 (3–4): 117–126. Bibcode:2007JHyd..343..117A. doi:10.1016/j.jhydrol.2007.06.013.
  11. ^ Paul Bierman, Milan Pavich, E-an Zen, and Marc Caffee, Determining Rates and Patterns of Bedrock Incision by Large Rivers 2007-09-13 at the Wayback Machine
  12. ^ Royden, Leigh; Perron, Taylor (2013-05-02). "Solutions of the stream power equation and application to the evolution of river longitudinal profiles". J. Geophys. Res. Earth Surf. 118 (2): 497–518. Bibcode:2013JGRF..118..497R. doi:10.1002/jgrf.20031. hdl:1721.1/85608. S2CID 15647009.
  13. ^ Campforts, Benjamin; Govers, Gerard (2015-07-08). "Keeping the edge: A numerical method that avoids knickpoint smearing when solving the stream power law". J. Geophys. Res. Earth Surf. 120 (7): 1189–1205. Bibcode:2015JGRF..120.1189C. doi:10.1002/2014JF003376.
  14. ^ Zahra, Tuba; Paudel, Uttam; Hayakawa, Yuichi; Oguchi, Takashi (2017-04-24). "Knickzone Extraction Tool (KET) – A new ArcGIS toolset for automatic extraction of knickzones from a DEM based on multi-scale stream gradients". Open Geosciences. 9 (1): 73–88. Bibcode:2017OGeo....9....6Z. doi:10.1515/geo-2017-0006. ISSN 2391-5447.

knickpoint, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, books, scholar, jstor, december, 2015,. This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Knickpoint news newspapers books scholar JSTOR December 2015 Learn how and when to remove this message In geomorphology a knickpoint or nickpoint is part of a river or channel where there is a sharp change in channel bed slope such as a waterfall or lake Knickpoints reflect different conditions and processes on the river often caused by previous erosion due to glaciation or variance in lithology In the cycle of erosion model knickpoints advance one cycle upstream or inland replacing an older cycle 1 A knickpoint that occurs at the head furthest upstream extent of a channel is called a headcut 2 Headcuts resulting in headward erosion are hallmarks of unstable expanding drainage features such as actively eroding gullies 3 The Horseshoe Falls one of the three Niagara Falls The falls are a knickpoint formed by slower erosion above the falls than below Knickpoints also occur on other planetary bodies that previously had or currently have surface liquids namely Mars 4 and Titan 5 On Mars the knickpoints have a common elevation that suggest a common sea level for a former Martian ocean 4 On Titan mountain valleys adjacent to the present day hydrocarbon seas show evidence of knickpoints and recent sea level change 5 Contents 1 Formation 2 Modern examples 2 1 Influenced by lithology 2 2 Influenced by tectonic activity 2 3 Influenced by glacial activity 3 Paleomorphology 3 1 Evidence of massive prehistoric flooding 3 2 Evidence within karst topography 3 3 Evidence of large scale base level drop 4 Movement 4 1 Mathematical modeling 5 Automated extraction in GIS 6 See also 7 ReferencesFormation editKnickpoints are formed by the influence of tectonics climate history and or lithology 6 For example uplift along a fault over which a river is flowing will often result in an unusually steep reach along a channel known as a knickzone Glaciation resulting in a hanging valley are often prime spots for knickpoints If lithology of the rock varies such as shale amongst igneous rock erosion will occur more steadily in the softer rock than the surrounding tougher rock Base level is the elevation of the surface of the water body into which a river ultimately drains usually the ocean A drop in base level causes a response by the river system to carve into the landscape This incision begins at the formation of a knickpoint and its upstream migration depends heavily upon the drainage area and so the discharge of the river material through which it cuts and how large the drop in base level was 7 Modern examples edit nbsp In this satellite image of Victoria Falls the gorges below the falls as well as developing crevasses below the surface of the river are visible As the knickpoint recedes upstream these crevasses will become in turn the location of the Falls Knickpoints include both waterfalls and some lakes These features are common in rivers with a sufficient slope i e enough change in elevation above sea level over their length to encourage degradation Influenced by lithology edit Variations in stability of the underlying rock influence development of a bedrock channeled river as the waters erode different rock types at different rates Victoria Falls on the Zambezi River is a spectacular example of this The gorges visible by satellite imagery illustrate the erosional processes behind the formation of the falls Here much of the surface rock is a massive basalt sill with large cracks filled with easily weathered sandstone made visible by the Zambezi s course across the land The gorges downstream of the falls through which it flows were eroded over time by the action of the water Influenced by tectonic activity edit Throughout New Zealand tectonic uplift and faulting are actively contributing to knickpoint initiation and recession The Waipoua River system on the North island has been studied and used to create mathematical models to predict the behavior of knickpoints 8 The study showed a direct correlation between upstream drainage area and rate of migration producing modeled data closely approximating the collected data The Waipoua River system incises through sediments for the most part as opposed to bedrock Influenced by glacial activity edit nbsp Bridalveil Fall in Yosemite flows over the edge of a glacially carved hanging valley Sharp changes in slope are common in rivers flowing through the heavily carved landscape left behind when glaciers retreat Glacial valleys as well as isostatic rebound resulting from the removal of the mass of glacial ice contribute to this Niagara Falls on the border of the United States and Canada is a characteristic example of knickpoint The falls have slowed in migration from approximately 1m per year as of 1900 to their modern 10 cm per year 9 The falls particularly Horseshoe Falls are dramatically steep and caused by glaciation The Great Lakes themselves lie in the depressions left behind by glaciers as the crust is still rebounding Bridalveil Fall in Yosemite Valley California pours over the lip of a hanging valley Paleomorphology edit nbsp Dry Falls Washington a prehistoric knickpoint Evidence of a knickpoint in the geologic past can be preserved in the shape of the bedrock below any subsequent depositions as well as within sedimentary depositions left unchanged by human or other activity Lakes characteristically fill in with sediment over time but waterfalls often erode away There are few obvious dry examples still visible today of prehistoric knickpoints Evidence of massive prehistoric flooding edit Dry Falls a 3 5 mi long precipice in central Washington is an example of an ancient knickpoint Geologic evidence strongly suggests that the water which formed this feature flowed over the Channeled Scablands bursting from the glacial lake Missoula during an event known as the Missoula Floods and into the Columbia River Gorge Evidence within karst topography edit On the Upper Cumberland River Tennessee there exist a series of hydrologically abandoned caves which still hold river deposited sediments These caves were the subject of an effort to measure the rate of knickpoint migration along the river as well as to approximate the discharge of the river over time 10 In karst topography a river dropping in level influences more than just its channel as there is no longer water flowing at a certain level caves and water tables will drop locally to the new level Evidence of large scale base level drop edit Large drainages into the oceans the world over can be seen to have continued over land which was once exposed whether due to tectonic subsidence sea level rise or other factors Bathymetric imagery is available for much of the United States western coast and in particular the ocean floor just offshore of rivers in the Pacific Northwest exhibit such underwater features In certain locations there are still knickpoints preserved in these drowned river channels and valleys A study conducted within the Mediterranean basin 7 focused on such features Here incision was caused by the closing of the Mediterranean at the end of the Miocene This sudden lack of ocean water influx allowed the basin to decrease in volume and increase in salinity and as a result of the drop in surface level many of the rivers which flow still today into the Mediterranean began to incise 7 Movement editAs is observed for many major waterfalls knickpoints migrate upstream due to bedrock erosion 11 leaving in their wake deep channels and abandoned floodplains which then become terraces Knickpoint retreat is easily demonstrated in some locations affected by postglacial isostatic response and relative sea level drop such as in Scotland In other areas dating of exposed bedrock terraces is more consistent with spatially uniform incision and persistence of the knickzone at about the same location A river having gained or lost potential energy with its changed slope will then proceed to work the knickpoints out of its system by either erosion in the case of waterfalls gained potential energy or deposition in the case of lakes lost potential energy in order for the river to reattain its smooth concave graded profile The rates of knickpoint migration in the case of waterfalls generally range between 1mm and 10 cm per year with some exceptional values 7 Mathematical modeling edit Knickpoint propagation is typically modelled with the semi empirical stream power law where the drainage basin size is used as a proxy for discharge which in turn has a positive nonlinear correlation to the rate of knickpoint migration Both analytical 12 and numerical solutions 13 have been proposed to solve the stream power law Automated extraction in GIS editKnickpoints and knickzones can be semiautomatically extracted from Digital Elevation Models in Geographic Information System software i e ArcGIS The problem with most of existing methods is that they are frequently subjective and require time consuming data processing A solution for these problems is a tool designed for ArcGIS called Knickzone Extraction Tool KET which vastly automates the extraction process 14 See also edit nbsp Environment portal Hydrology Stream gradientReferences edit Tinkler Keith J 2004 Knickpoint In Goudie A S ed Encyclopedia of Geomorphology pp 595 596 Bierman Paul Montgomery David 2013 Key Concepts in Geomorphology Knighton David 1998 Fluvial Forms and Processes A New Perspective a b Duran Sergio Coulthard Tom J Baynes Edwin R C 2019 10 22 Knickpoints in Martian channels indicate past ocean levels Scientific Reports 9 1 15153 Bibcode 2019NatSR 915153D doi 10 1038 s41598 019 51574 2 ISSN 2045 2322 PMC 6805925 PMID 31641171 a b Lucas Antoine Aharonson Oded Deledalle Charles Hayes Alexander G Kirk Randolph Howington Kraus Elpitha 2014 Insights into Titan s geology and hydrology based on enhanced image processing of Cassini RADAR data Journal of Geophysical Research Planets 119 10 2149 2166 Bibcode 2014JGRE 119 2149L doi 10 1002 2013JE004584 ISSN 2169 9100 Paul R Bierman David R Montgomery Key Concepts in Geomorphology Freeman 2013 ISBN 978 1429238601 a b c d Loget Nicolas Van Den Driessche Jean 2009 05 15 Wave train model for knickpoint migration Geomorphology 106 3 4 376 382 Bibcode 2009Geomo 106 376L doi 10 1016 j geomorph 2008 10 017 Crosby Benjamin T Whipple Kelin X 2006 12 06 Knickpoint initiation and distribution within fluvial networks 236 waterfalls in the Waipaoa River North Island New Zealand Geomorphology The Hydrology and Geomorphology of Bedrock Rivers 82 1 2 16 38 Bibcode 2006Geomo 82 16C doi 10 1016 j geomorph 2005 08 023 Hayakawa Yuichi S Matsukura Yukinori 2009 09 15 Factors influencing the recession rate of Niagara Falls since the 19th century Geomorphology 110 3 4 212 216 Bibcode 2009Geomo 110 212H doi 10 1016 j geomorph 2009 04 011 hdl 2241 103715 Anthony Darlene M Granger Darryl E 2007 09 20 An empirical stream power formulation for knickpoint retreat in Appalachian Plateau fluviokarst Journal of Hydrology 343 3 4 117 126 Bibcode 2007JHyd 343 117A doi 10 1016 j jhydrol 2007 06 013 Paul Bierman Milan Pavich E an Zen and Marc Caffee Determining Rates and Patterns of Bedrock Incision by Large Rivers Archived 2007 09 13 at the Wayback Machine Royden Leigh Perron Taylor 2013 05 02 Solutions of the stream power equation and application to the evolution of river longitudinal profiles J Geophys Res Earth Surf 118 2 497 518 Bibcode 2013JGRF 118 497R doi 10 1002 jgrf 20031 hdl 1721 1 85608 S2CID 15647009 Campforts Benjamin Govers Gerard 2015 07 08 Keeping the edge A numerical method that avoids knickpoint smearing when solving the stream power law J Geophys Res Earth Surf 120 7 1189 1205 Bibcode 2015JGRF 120 1189C doi 10 1002 2014JF003376 Zahra Tuba Paudel Uttam Hayakawa Yuichi Oguchi Takashi 2017 04 24 Knickzone Extraction Tool KET A new ArcGIS toolset for automatic extraction of knickzones from a DEM based on multi scale stream gradients Open Geosciences 9 1 73 88 Bibcode 2017OGeo 9 6Z doi 10 1515 geo 2017 0006 ISSN 2391 5447 Retrieved from https en wikipedia org w index php title Knickpoint amp oldid 1188244612, wikipedia, wiki, book, books, library,

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