Channel pattern: Difference between revisions

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==Bedrock vs. alluvial channels==

There are two main types of channels, [[bedrock]] and alluvial, which are present no matter the sub-classification. Bedrock channels are composed entirely of compacted rock, with only patches of [[alluvium]] scattered throughout. Because the bedrock is constantly exposed it takes much less [[stream power]] to carve the channel. The [[Hydraulics|hydraulic]] force of flowing water can push and pull detached joint blocks out of their initial position and roll or drag them downstream. [[Plucking (glaciation)|Plucking]] is common in jointed rocks, where this occurs.<ref>{{Cite book|url=https://www.worldcat.org/oclc/299847567|title=Geomorphology : a systematic analysis of late Cenozoic landforms|last=Leroy.|first=Bloom, Arthur|date=1998|publisher=Prentice-Hall|isbn=0135054966|oclc=299847567}}</ref>

Alluvial channels are much more common and can be large or small. All large rivers, and most small ones, have channels that are usually lined with alluvium, sediment that was carried to that channel reach by the river and that eventually will be carried farther [[wikt:downstream|downstream]].<ref>{{Cite journal|last=Diplas|first=Panayiotis|title=Characteristics of Self‐Formed Straight Channels|url=http://ascelibrary.org/doi/pdf/10.1061/(ASCE)0733-9429(1990)116:5(707)|journal=Journal of Hydraulic Engineering|language=en|volume=116|issue=5|pages=707–728|doi=10.1061/(asce)0733-9429(1990)116:5(707)|year=1990}}</ref> This lining of alluvium creates a protective shield over the bedrock, which means it takes a much greater stream power to carve the channel.

==Braided channels==

There are a few distinctly different channel types based on their geological structure and [[Depositional environment|depositional]] environment. [[Braided river]]s carry fairly coarse-grained sediment down a fairly steep gradient. They typically exhibit numerous channels that split off and rejoin each other to give a braided appearance. Additionally, the water [[Discharge (hydrology)|discharge]] tends to be highly variable. Consequently, braided rivers usually exist near mountainous regions, especially those with glaciers.<ref>{{Cite book|url=https://www.worldcat.org/oclc/489065099|title=Geology : an introduction to physical geology|last=Stanley|first=Chernicoff,|last2=L.|first2=Whitney, Donna|date=2007|publisher=Pearson Prentice Hall|isbn=978-0131474642|oclc=489065099}}</ref> These braided channels usually occur in [[Tectonics|tectonically active]] environments and have a larger sediment load due to varying water flow and discharge.

==Anastomosed channels==

Often confused with braided channels, [[Anastomosis|anastomosing]] is reserved for a type of river with multiple, interconnected, coexisting channel belts on alluvial plains. Based on its geomorphology, saucer-shaped islands called [[Flood basin|flood-basins]] characterize anastomosing rivers.<ref>{{cite journal|last1=Makaske|first1=Bart|title=Anastomosing rivers: a review of their classification, origin and sedimentary products|journal=Earth-Science Reviews|date=2001|volume=53|issue=3-43–4|pages=149–196|doi=10.1016/S0012-8252(00)00038-6|url=http://www.geo.arizona.edu/geo5xx/geos544/pdfs/fluvial/makaske.pdf|access-date=2017-05-16|archive-url=https://web.archive.org/web/20161011091819/http://www.geo.arizona.edu/geo5xx/geos544/pdfs/fluvial/makaske.pdf|archive-date=2016-10-11|dead-url-status=yesdead|bibcode=2001ESRv...53..149M}}</ref> These channels are classified as a composite form of which the individual channel belts may have braided, [[meander]]ing or [[Straight River (central Minnesota)|straight channels]]. Although similar to, and even encompass other channel types, anastomosed rivers are their own entity and have just begun to be studied by [[geologist]]s, revealing that much is still unknown.

[[Fluvial]] processes form several '''channel patterns''', including:

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*[[Braided river]]s, which form in (tectonically active) areas that have a larger sedimentary load than the discharge of the river and a high gradient.

*[[Meandering river]]s, which form a [[sinuous]] path in a usually low-gradient plain toward the end of a fluvial system.

*[[Anastomosis#Geography and hydrology|Anastomosed river]] is a rare case of a relatively straight, complicated vertical sequence of river deposits with banks held together by dense [[vegetation]].

== See also ==

*{{annotated link|Channel types}}

*{{annotated link|Depositional environment}}

*{{annotated link|SedimentaryDrainage structuressystem (geomorphology)}}

*{{annotated link|Fluvial landforms}}

*{{annotated link|Fluvial processes}}

*{{annotated link|ListSedimentary of landforms#Fluvial landforms|Fluvial landformsstructures}}

== References ==

{{Reflistreflist}}

== Further reading==

*Prothero, D. R. and Schwab, F., 1996, Sedimentary Geology, pg. 137-167, {{ISBN|0-7167-2726-9}}

{{River morphology}}

{{Rivers, streams and springs}}

[[Category:Geomorphology]]