A natural flow of water from underground to the surface is a/an

Spring (hydrology)

A spring may be the result of karst topography where surface water has infiltrated the Earth's surface (recharge area), becoming part of the area groundwater. The groundwater then travels through a network of cracks and fissure-openings ranging from intergranular spaces to large caves. The water eventually emerges from below the surface, in the form of a karst springs.

A natural flow of water from an underground to the surface is a spring.