A guide to the Italian karst landscapes: the Carso of Trieste (which gave the phenomenon its name), the Puglia Murge, the Gargano, the Plateau of the Seven
The term "karst" (carsico in Italian, Karst in German) derives from the Carso, the limestone plateau that extends between Trieste, Friuli, and Slovenia. This means that every time a geologist describes a karst phenomenon anywhere in the world, from the Amazon to China, from Kentucky to Madagascar, they're using an Italian word. The karst landscapes in Italy aren't just beautiful to see: they're the original model of a global geomorphological phenomenon.
The Carso is a limestone plateau of 500 km² between Trieste, Gorizia, and the Slovenian border, with elevations between 200 and 600 m. The substrate is Mesozoic limestone (Cretaceous, 65-145 million years ago), practically pure, with no clay intercalations that would slow the infiltration of the water. The result: the rainwater (slightly acidic from the dissolved CO2) penetrates the limestone, dissolves it, creates cavities, galleries, springs. On the surface the traces remain: doline (circular depressions from collapse or dissolution), inghiottitoi (vertical openings where the water descends), limestone pavements (rock surfaces with parallel grooves), karst plains with no surface rivers.
The vegetation of the Carso is Mediterranean with eastern elements, a unique combination. The downy oak (Quercus pubescens), the hop hornbeam (Ostrya carpinifolia), the manna ash (Fraxinus ornus) dominate the woods. The bora, the dry katabatic wind that can reach 200 km/h, shapes the vegetation dramatically: trees with asymmetric crowns, permanently bent toward the east. In Trieste, the bora is part of the cultural identity: the bars have metal rings on the outer walls that passersby hold on to during the most intense gusts.
The Murge, the Puglia plateau between Bari, Taranto, and Foggia, are the most extensive karst territory of southern Italy: about 4,500 km² of Cretaceous limestone (the same 65-145 million years as the Trieste Carso). The high Murge (700 m the highest peak, Murgia Timone) and the low Murge (200-300 m) form the geological floor on which Bari, Altamura, Gravina, and Matera rest.
Gravina in Puglia (BA) is built on a gravina, a Puglia term for a karst gorge. The canyon of the Gravina Creek, up to 80 m deep, cuts through the city: the medieval historic center develops literally on the edge of this precipice. The Puglia gravine are the same karst morphologies of the Trieste Carso, but with 2,000 years of human history overlaid: rock settlements, churches carved into the rock, masserie built on the gorge walls.
The Gargano (the "promontory" of Puglia, "the spur") is a limestone massif of 1,800 km² that emerges from the plain of the Tavoliere like an island of rock. Geologically, the Gargano isn't Puglian, it's a fragment of African crust that welded itself to the Italian peninsula in the Cretaceous. Its limestone is of a different type from the Murge, with enormous doline (the largest in Italy on the surface), ring doline, internal karst lakes.
The Lake of Lesina and the Lake of Varano, coastal lagoons on the north coast of the Gargano, are closely linked to the karst geomorphology: they formed by the subsidence of coastal karst areas and the subsequent entry of the sea. The Caves of Castellana (see the caves guide) are in the southern Gargano.
The Asiago Plateau (VI), also called the "Plateau of the Seven Comuni", is a limestone plateau at 1,000-2,000 m of elevation in the Venetian Prealps. Developed karst morphology: doline, sinkholes, limestone pavements, an almost total absence of surface rivers. The Posina, the Astico, and their tributaries are born at the foot of the plateau from karst springs. The Plateau is the theater of the Great War, the battles of 1916-17 (the Strafexpedition and the Italian counteroffensive) took place in this landscape of karst stone.
| Term | Definition | Where to find them in Italy |
|---|---|---|
| Dolina | Circular depression from dissolution or collapse | Carso TS, Murge, Gargano |
| Inghiottitoio (sinkhole) | Vertical opening where the water disappears | Trieste Carso (hundreds) |
| Limestone pavement (Karren) | Limestone surface with parallel grooves from erosion | Dolomites, Carso, Apennines |
| Polje | Large flat karst depression | Friuli-Venezia Giulia |
| Gravina | Puglia term for a karst gorge | Murge (Gravina, Laterza, Taranto) |
| Risorgiva (resurgence) | Karst water spring in the plain | Po valley (Veneto, Friuli) |
Because the Trieste Carso was the first area studied scientifically by European geologists in the 19th century, it was near the universities of Vienna, Trieste, and Ljubljana, easily accessible, with extremely developed and visible karst morphologies. The Slovenian geographer Jovan Cvijić published "Das Karstphänomen" in 1893, the systematic study of karst that established the terminology used worldwide today. Cvijić was of the Viennese school and worked mainly on the Trieste-Istrian Carso.
Practically yes. Every Italian region has at least limestone areas with karst phenomena, even if of different intensity. The regions with the most developed karst: Friuli-Venezia Giulia (Trieste Carso), Puglia (Murge, Gargano, Salento), Campania (the Campanian Apennines), Sardinia (Supramonte, the Nuoro area), Marche (Frasassi), Tuscany (Garfagnana, the Apuan Alps). The Po valley and the sandy coasts are the areas with the least karst.
Yes. The Trieste Carso has a network of well-marked CAI trails. The best-known route is the Trieste-Lipica (15 km, difficulty E, walkable in 4 hours) which crosses doline, downy-oak groves, and karst pastures. The Rilke Trail (from Duino to Sistiana, 2 km, a view over the Gulf of Trieste) is shorter and more scenic. The Val Rosandra is also suited to climbing. Maps: CAI Trieste distributes trail maps, also downloadable from www.caitrieste.it.
Because the limestone is porous, the rainwater infiltrates directly through the fractures and the joints of the rock, without flowing on the surface. The Timavo, one of the most mysterious rivers in Italy, runs about 40 km of underground galleries in the Trieste Carso before re-emerging at San Giovanni di Duino with a flow of 56 m³/s, larger than many Italian rivers that flow on the surface. The Greeks and the Romans knew the Timavo and cite it as a sacred river.
The resurgences of the Po valley (Veneto, Friuli, eastern Lombardy) are the most hidden manifestation of Italian karst: the water that falls on the Prealpine hill band infiltrates the subsoil and re-emerges in the plain as springs (fontanili), springs of constant temperature (10-12°C) that don't freeze in winter and don't overheat in summer. Along the line of the fontanili (from Turin to Venice) mills, rice paddies (the constant temperature is ideal for rice), fish farms, and the "prati marcitoi" were built, winter irrigation systems that keep the grass green even when it's below zero outside.
A stalactite grows on average between 0.1 and 10 cm every 100 years, the variability is enormous and depends on the amount of percolating water and the calcium concentration. In ideal conditions (high humidity, abundant calcareous water), some stalactites grow 1 mm/year. The 2-3 meter stalactites in the Italian caves (Frasassi, Castellana) are therefore between 20,000 and 200,000 years old. The precise dating is done with the uranium-thorium method (U-Th), the same used for the ice cores.
The "terra rossa" (red earth in geology) of the Trieste Carso is the insoluble residue that remains after the dissolution of the limestone: iron and aluminum oxides with clay, a red-orange color from the presence of hematite (Fe2O3). The limestone dissolves completely in the acidic water; what remains (1-5% of the original rock) accumulates in the doline and the cavities as a reddish sediment. The Carso red earth is particularly fertile, traditionally used for vineyards and olive groves.
The Polje of Canale d'Isonzo (GO) is the largest karst plain in Friuli: an elliptical depression of 7 km x 2 km that floods periodically due to the rise of the karst waters from the subsoil. In winter and spring, the polje can be completely flooded, a temporary lake where in summer fields are cultivated. The flood-drainage cycle is natural and seasonal: the sinkholes at the edge of the polje drain the water into the underground system of the Isonzo. A phenomenon rarely described in the guides, visible from the SS56 between Caporetto (Nova Gorica, Slovenia) and Gorizia.
The Limestone pavements of Punta Mesco (Monterosso al Mare, SP) are one of the geological rarities of Liguria: a field of karren (dissolution grooves) directly on the cliff of the Punta Mesco promontory, reachable via the Sentiero Azzurro of the Cinque Terre. A sea view, karst morphology, and Mediterranean biodiversity in a postcard setting.
The Trieste Carso is reachable by bus from central Trieste (lines 39, 40, 42, €1.35 ticket) or by car (the SS58, the Strada Provinciale del Carso). The ideal starting point for an excursion: the village of Opicina (TS), the Carso village at 350 m above the sea, 8 km from Trieste. From there CAI trails open toward San Dorligo della Valle, toward the Slovenian border (Trebiciano, where the Abisso di Trebiciano is found, the largest explorable sinkhole of the Carso, 329 m deep, speleological visits organized by the GST), toward Rupingrande and the Caves of San Canziano (Slovenia, UNESCO Heritage, 30 min by car from the border).
The Rilke Trail, 2 km between Sistiana and Duino (TS) on the edge of the limestone cliff, bears the name of the poet Rainer Maria Rilke, who stayed at the Castle of Duino in 1912 and here composed the first Duino Elegies. The trail offers the most beautiful view of the Gulf of Trieste from the west: the pale limestone of the cliff, the intense blue sea of the Gulf of Trieste, the Castle of Duino in the foreground. Duration: 45 minutes. Difficulty: low. Access: bus from Trieste (line 44) the Sistiana stop.
A typical one-day itinerary: morning, the Grotta Gigante (Sgonico, TS, €13, the largest tourist room in the world by volume, 98 m high, 280 m long, a constant temperature of 11°C); lunch, a traditional Osmiza (Carso farms that sell wine, cheese, ham, and home bread, identified by the pine or hay branch displayed outside the door, a symbol of being open); afternoon, the Rilke Trail from Sistiana to Duino; evening, an aperitivo in Trieste at a historic café (Caffè San Marco, Via Cesare Battisti 18, open since 1914; or Caffè degli Specchi in Piazza Unità d'Italia). Day budget: €25-40 excluding transport.
Every millimeter of rain that falls on the Trieste Carso has two possibilities: evaporation (about 55%) or infiltration into the subsoil (45%). That water which infiltrates makes on average 30-40 years of underground journey before re-emerging as a spring at the base of the plateau. The Timavo, the most mysterious of the Italian karst rivers, flows for 40 km of underground galleries in the Carso, enters Slovenian territory near Škocjan and re-emerges at San Giovanni di Duino (TS) with an average flow of 56 m³/s (more than the Tiber in Rome in normal conditions). The Romans venerated the Timavo as a sacred river, Virgil cites it in the Aeneid ("the Timavo, issuing from a single gorge, drives the sea through seven mouths and resounds with a roar"). The source of the Timavo at San Giovanni di Duino can be visited: it's simply a stretch of stream that emerges among the reeds, no sign, no infrastructure, water that appears from nowhere at 56 cubic meters a second.