The present-day Grønli–Seter karst aquifer in Rana is fed by a surface stream that invades a relict cave system, so that the present hydrology is constrained by pre-existing geometry. This type of karst aquifer is quite common in the glacially sculptured landscape of Norway, where speleogenesis displays a strong imprint from glacier-ice contact. The Grønli–Seter cave system is situated in the hillside of Røvassdalen, with passage morphology and palaeoflow marks indicating development below the watertable and by ascending water flow in the presence of a glacier filling up the valley. The aquifer has a mean annual discharge of about 0.13 m3 s-1, which makes up about half of the total runoff from Strokbekken from where it is sourced. Hydrograph and quantitative dye-tracer experiments demonstrated that the aquifer is totally dominated by conduits and comprises three sections with distinctly different cross-sectional areas.
The lower part of the traced aquifer comprises essentially phreatic (submerged) conduits with a mean cross-sectional area of about 4.5 m2 and a static volume of minimum 4000 m3 . In the upper sections, the ratio of submerged, water-filled passages is lower, and the cross-sectional area of the water flow is smaller, but with a greater increase during floods. The maximum estimate of the total aquifer volume is 10,000 m3 (at a discharge of about 0.2 m3 s-1). The total hardness (the concentration of Ca2+ and Mg2+ in the water) has been measured in the low range of 15 to 36 mg CaCO3 equivalents per litre, which is normal for settings like this. The highest transport rates of calcite leaving the aquifer are related to the highest discharges. The evolution of invasion aquifers like this one is therefore suggested to accelerate when the recharge conditions are changed, i.e., due to glacial erosion, so that the entire surface stream is captured by the stream sink