Editing Coast (section)

==Formation {{anchor|Formation of Coasts}}==
[[File:Porto Covo pano April 2009-4.jpg|thumb|upright=1.2|Atlantic rocky coastline, showing a surf area. [[Porto Covo]], west coast of Portugal]]
[[File:Spiaggia rosa, isola di budelli, sardegna.jpg|thumb|upright=1.2|Seaside in [[Budelli]], Italy. Budelli beach is famous for the color of its sand, which is pink due to the presence of fragments of a microorganism called ''Miniacina miniacea''.<ref>{{cite web|url=https://www.sardegnaturismo.it/it/esplora/spiaggia-rosa|title=Spiaggia Rosa|date=20 November 2015 |access-date=27 December 2024|language=it}}</ref>]]

[[Tide]]s often determine the range over which [[sediment]] is deposited or eroded. Areas with high tidal ranges allow waves to reach farther up the shore, and areas with lower tidal ranges produce deposition at a smaller elevation interval. The tidal range is influenced by the size and shape of the coastline. Tides do not typically cause erosion by themselves; however, [[tidal bore]]s can erode as the waves surge up the river [[Estuary|estuaries]] from the ocean.<ref>{{Cite book|last=Davidson|first=Jon P.|title=Exploring earth: an introduction to physical geology|date=2002|publisher=Prentice Hall|others=Walter E. Reed, Paul M. Davis|isbn=0-13-018372-5|edition=2nd|location=Upper Saddle River, NJ|oclc=45917172}}</ref>{{rp|421}}

Geologists classify coasts on the basis of [[tidal range]] into ''macrotidal coasts'' with a tidal range greater than {{Convert|4|m|ft|abbr=on}}; ''mesotidal coasts'' with a tidal range of {{Convert|2 to 4|m|ft|abbr=on|sigfig=2}}; and ''microtidal coasts'' with a tidal range of less than {{Convert|2|m|ft|abbr=on|sigfig=1}}. The distinction between macrotidal and mesotidal coasts is more important. Macrotidal coasts lack [[barrier islands]] and [[lagoons]], and are characterized by funnel-shaped estuaries containing sand ridges aligned with tidal currents. Wave action is much more important for determining [[bedforms]] of sediments deposited along mesotidal and microtidal coasts than in macrotidal coasts.<ref>{{cite book |last1=Blatt |first1=Harvey |last2=Middleton |first2=Gerard |last3=Murray |first3=Raymond |title=Origin of sedimentary rocks |date=1980 |publisher=Prentice-Hall |location=Englewood Cliffs, N.J. |isbn=0-13-642710-3 |edition=2d |pages=656–659}}</ref>

Waves erode coastline as they break on shore releasing their energy; the larger the wave the more energy it releases and the more sediment it moves. Coastlines with longer shores have more room for the waves to disperse their energy, while coasts with cliffs and short shore faces give little room for the wave energy to be dispersed. In these areas, the wave energy breaking against the cliffs is higher, and air and water are compressed into cracks in the rock, forcing the rock apart, breaking it down. Sediment deposited by waves comes from eroded cliff faces and is moved along the coastline by the waves. This forms an [[abrasion coast|abrasion]] or [[cliffed coast]].

Sediment deposited by rivers is the dominant influence on the amount of sediment located in the case of coastlines that have estuaries.<ref name=":2">{{Cite book|last=Easterbrook|first=Don J.|title=Surface processes and landforms|date=1999|publisher=Prentice Hall|isbn=0-13-860958-6|edition=2nd|location=Upper Saddle River, N.J.|oclc=39890526}}</ref> Today, riverine deposition at the coast is often blocked by dams and other human regulatory devices, which remove the sediment from the stream by causing it to be deposited inland. Coral reefs are a provider of sediment for coastlines of tropical islands.<ref>{{Cite web|title=How is beach sand created? - Woods Hole Oceanographic Institution|url=https://www.whoi.edu/how-is-beach-sand-created/|url-status=live|access-date=2021-08-10|website=Woods Hole Oceanographic Institution|language=|archive-url=https://web.archive.org/web/20210628213754/https://www.whoi.edu/how-is-beach-sand-created/ |archive-date=2021-06-28 }}</ref>

Like the ocean which shapes them, coasts are a dynamic environment with constant change. The [[Earth]]'s natural processes, particularly [[sea level rise]]s, waves and various [[weather]] phenomena, have resulted in the [[erosion]], [[Accretion (geology)|accretion]] and reshaping of coasts as well as flooding and creation of [[continental shelf|continental shelves]] and drowned river valleys ([[ria]]s).