Editing Natural arch (section)

==Coastline==
[[File:Malta Gozo, Azure Window (10264176345).jpg|thumb|left|The [[Azure Window]], [[Malta]], before it collapsed in 2017]]
[[File:Darwinarch.jpg |thumb|left|[[Darwin's Arch]], [[Galápagos Islands]], [[Ecuador]], before it collapsed in 2021]]
On coasts two different types of arches can form depending on the geology. On [[discordant coastline]]s rock types run at 90° to the coast. [[wave|Wave refraction]] concentrates the wave energy on the headland, and an arch forms when [[cave]]s break through the headland. Two examples of this type of arch are [[London Bridge (Victoria)|London Bridge]] in [[Victoria (Australia)|Victoria]], Australia, and [[Neill Island]] in the [[Andaman Islands]], India. When these arches eventually collapse, they form [[Stack (geology)|stacks]] and stumps. On [[concordant coastline]]s rock types run parallel to the coastline, with weak rock such as [[shale]] protected by stronger rock such as [[limestone]]. The wave action along concordant coastlines breaks through the strong rock and then erodes the weak rock very quickly. Good examples of this type of arch are the [[Durdle Door]] and [[Stair Hole]] near [[Lulworth Cove]] on [[Dorset]]'s [[Jurassic Coast]] in south England. When Stair Hole eventually collapses it will form a [[cove]].