Right, sorry to wind this back a bit.
Fortunately, Guardians Reborn is blessed with geologists and we have formulated a hypothesis.
The answer is as follows:
The mountains of western Correllia were formed by volcanic activity.
As such, this isolated range is riddled with the caldera and vents of extinct volcanoes.
This diagram shows the situation:
The stronghold sits on a secondary vent of a larger volcanic peak; as such, channels exist within the rock. The volcanic crater has now been colonized by a cirque glacier and meltwater from this now flows back down the lava shaft into the vent system. The primary vent is now plugged with a non-porous high-silica rhyolite and so the water is channelled into the secondary vents, including the substantial formation upon which the stronghold is situated.
As the source of the water is at a higher elevation than the secondary vent, a Artesian well effect causes water to flow up the vent and to the surface.
As we can see the height differential is significant.