Karst forms

In the watersheds of the North-Estonian plateau, the rain water infiltrates through thin Quaternary cover and limestone pores and cracks. Striving for the springs and rivers, the water dissolves the surrounding rocks, forming underground karst channels. Smooth surface topography leads to the formation of channels in the uppermost bedrock strata or just below the Quaternary cover. When the ceilings of the channels collapse, the surface karst features — karst cones and dry valleys — are formed.

The karst channels have many levels. The lower levels are always filled with water, and the higher levels are flooded in high water. The water level in wells may vary by 10 or more metres. The connection between surface and underground water is marked by swallow holes, underground rivers (Kuivajõe, Jõelähtme) and numerous karst springs. There are perhaps more than a thousand karst cones up to 5–6 m deep as well as other surface karst features in Estonia. Three hundred and fifty-two surface karst features have been noted in the Pandivere Upland. The largest karst fields — Kostivere, Kata (Tuhala), Kuimetsa and Pae — are located in the Harju limestone plateau.

Other major karst fields are Savalduma in the Pandivere Upland and Uhaku in the Viru plateau. Among about 30 karst caves, the longest (54 m) was recently discovered in the Kata karst field. There are hundreds of large karst springs in Estonian limestone plateaus. The most numerous and water-rich springs (10 to 100 l/s and above) are on the slopes of the Pandivere Upland, from where the Pärnu, Jägala, Valgejõgi, Kunda, Avijõgi, Pedja and Põltsamaa rivers begin.

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