There are two situations: The first is pressure or flow from a higher place. For example, the top of a certain mountain is a lag layer with good sealing. Rainwater will flow along the cracks in the rocks and flow downward. half-way. He comes out of a gap in the mountainside. Another situation is that there is a well-sealed lower layer below the ground surface throughout the area, and there are only cracks near the mountainous areas. At that time, water will enter from the highest mountains and flow out of the mountains. low mountain areas.
The second situation is that of geothermal energy. It is more common in volcanic areas. Groundwater is heated by geothermal heat and escapes from the ground, or it turns into water vapor that rises when it encounters lower temperature rocks at higher altitudes, itcool and flow into a liquid.
There may be other reasons, but I just know thanks. I hope I can give you a reference