When two sea caves on opposite sides of a headland are eroded and unite a (n) ___ forms

When two sea caves on opposite sides of a headland are eroded and unite a sea arch forms.

Sea arch is a natural opening and a type of erosional landform that forms due to different rates of erosion, usually as a result of different resistance of bedrock. Sea arch is made up of a soft rock that eroded as waves hit land which creates caves in the rock. Two caves may become jointed over some time to form a tunnel and eventually, a sea arch.