Question

How are lagoons are formed

Answer 1

Coral Reef lagoons are formed at the barrier reefs and atolls when water is confined in an area by the growth of coral colonies around a coast or island.  

Whereas, coastal lagoons, other than coral reefs origin, are formed mainly at the emerged coasts which are dominated by the landforms of deposition viz. bars, barrier bars, spits, hooks, etc. These depositional landform sometimes cut a bay or any other embayment along the coast from the sea and thus making lagoons. Needless to mention that these lagoons are, in turn, filled up with the sediments brought by the rivers, etc. from the land and form coastal plain.