Which of the following are known as coastlines of submergence?

Answer: (b) Ria Coasts

Ria coasts form when the sea floods river valleys — submergence.

The idea

Submergence means sea level rises relative to the land, flooding former valleys. It can happen because the sea rises or because the coast sinks. The drowned valley’s original shape helps distinguish one submerged coast from another.

A river cuts a valley on land → Sea level rises relative to the coast → Seawater enters the lower valley → Branches of the valley become inlets → A ria coastline develops

Why the others are wrong

(a) Uplifted lowland is emergence.

(c) Emergent upland is emergence.

Elimination technique

Uplifted and emergent land describe emergence, the opposite of drowning. A ria is the submerged river-valley option.

Also know

Rias are drowned river valleys; fjords are drowned glacial valleys with steep sides and deep basins. Raised beaches and marine terraces indicate emergence. A coast can have evidence of both past emergence and later submergence. Relative sea-level change combines changes in ocean level with local movement of land.