COASTS formed by the submergence of U-shaped glacial troughs. These are not a RESULT of any UNDERGROUND water action.● The sinkhole is a cavity in the ground which is CAUSED by water erosion and provides a route for SURFACE water to disappear underground.● Stalactites are the tapering structures which are formed of calcium salts deposited by dripping water. They are found hanging like icicles from the roof of a cave.● A stalagmite is a tapering column or a mound rising from the floor of a cave.