There are also the so-called Karst basins or "polie": those ones, usually of tectonic origin, are close depressions of big dimensions with a plate bottom, steep slopes and an oval or very long contour, mostly crossed by waters and sometimes completely flooded. Large rocky outcrops showing various dissolution forms are very diffused: they are called hollowed fields (Karrenfeld) and show little corrosion forms. We find as well some fields of crushed stone (the Karst "grize"), caused by differential dissolution forms of particular types of rock. We have also the so-called covered Karst (Grüner Karst), formed of an earthy yellow-reddish mantel, named "terra rossa" (red earth). The Karst lakes, situated on the bottom of the Karst basins, have no superficial emissaries and live and flow under ground. The Lake of Doberdò offers a beautiful example of this phenomenon

CAVES
In the Karst territory we constantly find some hollows such as potholes, caves or caverns, developing for hundreds of metres and sometimes also for kilometres inside the Karst rocks. These holes in the rocky mass are generally caused by the dissolution of the meteoric circulating waters or of the ones coming from the areas outside the Karst. The hollows are mostly named "potholes" when they develop mainly in a vertical way, "galleries" if they develop mainly in a sub-horizontal way. Numerous underground watercourses, springs and Karst lakes are present as well. The underground watercourses usually originate by following the superficial water that sinks into big empty holes and emerges at the end of the Karst massif. Perhaps the most fascinating aspect is the lack of knowledge of the underground track of these waters, we can only know what has been discovered by speleological explorations and by indirect researches done with physical, chemical and biological methods.



The course of these water streams is much more irregular compared to that one of the superficial rivers, in consequence of the rather irregular way of the fracturing systems of the Karst massif. The underground waters emerge in the Karst springs, while the watercourses that are absorbed or swallowed by the Karst massif, emerge in the Karst springs. Good examples of these ones are the sources of the river Timavo.


FRIULI VENEZIA GIULIA CAVES
A list of the famous caves of Friuli Venezia Giula follows:

List of most deep caves:
1. Complesso del Foran del Muss (Alpi Giulie) - 990m
2. Abisso Led Zeppelin (Alpi Giulie) - 960m
3. Complesso del Col delle Erbe (Alpi Giulie) - 880m
4. Abisso Modonutti Savoia (Alpi Giulie) - 805m
5. Complesso S20 - S31 - FDZ 2 (Alpi Giulie) - 760m
6. Abisso "Amore quanto latte" (Alpi Giulie) - 745m
7. Abisso Capitan Findus (Alpi Giulie) - 740m
8. Abisso a SE della quota 1972 (ET5) - (Alpi Giulie) - 726m
9. Abisso II del Poviz (Gronda Pipote) - (Alpi Giulie) - 720m
10. Abisso Paolo Fonda (Alpi Giulie) - 705m
11. Complesso del Monte Cavallo di Pontebba (Alpi Carniche) - 690m
12. Abisso Cesare Prez (Alpi Giulie) - 654m
13. Abisso Citta' di Udine (Alpi Giulie) - 625m
14. Abisso Maurizio Martini (Alpi Giulie) - 625m
15. Abisso Eugenio Boegan (Alpi Giulie) - 624m
16. Abisso OP III (Alpi Giulie) - 624m
17. Sistema NET 10 - Abisso del Pero (Alpi Giulie) - 609m
18. Complesso Vianello-Buse d'Ajar (Monte Canin) - 585m
19. Abisso Sisma (Alpi Giulie) - 515m
20. Abisso Giovan Battista De Gasperi (Alpi Giulie) - 512m
21. Abisso Roberto Pahor (Prealpi Giulie) - 495m
22. Abisso Paolo Picciola (Alpi Giulie) - 469m
23. Buca Mongana (Prealpi Carniche) - 450m
24. Abisso I di Mogenza Piccola (Alpi Giulie) - 430m
25. Abisso delle Pozze (Alpi Giulie) - 427m
26. Abisso dei Dannati (Alpi Giulie) - 425m
27. Buca delle Manzette (Prealpi Carniche) - 425m
28. Abisso a SW del Col delle Erbe (Alpi Giulie) - 420m
29. Abisso degli Increduli (Alpi Giulie) - 410m
30. Complesso del Bila Pec (Alpi Giulie) - 404m
31. Fontanin del Fratte (Prealpi Carniche) - 396m
32. Grotta Claudio Skilan (Carso) - 375m
33. Grotta di Trebiciano (Carso) - 350m
34. Complesso Mainarda-Noglar-La Val-Battei (Prealpi Carniche) - 332m
35. Abisso degli Incubi (Alpi Carniche) - 318m
36. Abisso II del Pic Majot (Alpi Giulie) - 308m
37. Gran Meandro delle Cime Mogenza (Alpi Giulie) – 305m
38. Abisso della Funivia (Alpi Giulie) - 303m

List of most big caves
1. Complesso del Col delle Erbe (Alpi Giulie) - 18.000m
2. Complesso del Foran del Muss (Alpi Giulie) - 16.500m
3. Grotta Nuova di Villanova (Prealpi Giulie) - 7.090m
4. Complesso Mainarda-Noglar-La Val-Battei (Prealpi Carniche) - 6.724m
5. Complesso Vianello-Buse d'Ajar (Monte Canin) - 6.320m
6. Grotta Claudio Skilan (Carso) - 6.200m
7. Complesso del Monte Cavallo di Pontebba (Alpi Carniche) - 5.700m
8. Risorgiva di Eolo (Prealpi Carniche) - 5.298m
9. Landri Scur (Prealpi Carniche) - 4.800m
10. Grotta di San Giovanni d'Antro (Prealpi Giulie) - 4.500m
11. Grotta Gualtiero Savi (Carso) - 4.000m
12. Grotta Doviza (Prealpi Giulie) - 3.795m
13. Abisso Led Zeppelin (Alpi Giulie) - 3.691m
14. Grotta Egidio Feruglio (Prealpi Giulie) - 3.500m
15. Rotule Spezzate (Alpi Giulie) - circa 3.500m
16. Fessura del Vento (Carso) - 2.626m
17. Grotta della Foos (Prealpi Carniche) - 2.625m
18. Pod Lanisce (Prealpi Giulie) - 2.100m
19. Buca Mongana (Prealpi Carniche) - 2.000m
20. Risorgiva Da Rio (Alpi Carniche ) 2.000 m
Complesso del Timavo (Carso) -