EarthCache – Dolines (Sinkholes) of Durmitor

Introduction

Durmitor, one of the most striking massifs of the Dinarides and a UNESCO World Heritage Site, is a landscape shaped by the combined action of tectonics, glaciation, and intense karstification. Its carbonate bedrock (Triassic–Jurassic limestones and dolomites) is predisposed to dissolution by water charged with carbon dioxide, which over tens of thousands of years has given rise to a spectacular variety of karst landforms.

Among the most characteristic surface forms of the Durmitor karst are dolines (sinkholes, Slovak: závrty, local: vrtače). They occur here in exceptional density, size, and morphological diversity, creating a textbook example of karst topography that attracts scientists, students, and hikers from around the world.

Geological Background

The foundation of the Durmitor massif is thickly bedded Mesozoic carbonate rock, predominantly limestones and dolomites, uplifted during the Alpine orogeny. These rocks are fractured, jointed, and permeable. Rainwater and snowmelt infiltrate rapidly, becoming enriched with carbon dioxide from soils and vegetation, and thus form a weak carbonic acid. Over geological time, this slightly acidic water dissolves calcite and dolomite, enlarging fractures and bedding planes and creating underground voids.

When such dissolution proceeds long enough, the surface becomes pitted with closed depressions. These are dolines: negative landforms with no surface outlet, where water disappears underground.

Morphology of Dolines in Durmitor

Dolines vary in size from a few meters to more than 200 m in diameter and can reach depths of several tens of meters. Their shapes include:

• Bowl-shaped (solution dolines): Gentle slopes, formed by slow chemical lowering of the surface.
• Conical dolines: Steeper slopes, often in areas with less soil cover.
• Collapse dolines: Steep-walled depressions, formed when the roof of an underground void gives way.
• Compound dolines: Overlapping depressions that coalesce into larger, irregular basins.

In Durmitor, dolines are frequently arranged in dense fields, sometimes called “doline clusters” or “doline poljes.” These clusters reflect uniform lithology, structural predispositions, and the role of Pleistocene glaciations.

Glacial Overprint on Dolines

During the Quaternary ice ages, glaciers extended across Durmitor. The ice modified pre-existing karst depressions, deepened some dolines, and deposited morainic material inside others. After glacial retreat, karst processes resumed, reactivating sinkholes and producing hybrid forms. This glaciokarstic superposition is unique and can be directly observed in many dolines near Sedlo pass.

Hydrology and Ecology

Dolines play a key role in Durmitor’s hydrological system. They funnel surface runoff underground, feeding karst aquifers and powerful springs at lower elevations (e.g., sources of Tara River). Because dolines trap soil and moisture, they also host distinctive microclimates and ecosystems. Many contain denser vegetation, patches of meadow, or even small groves of trees, in contrast to the barren karst ridges around them. Snow often lingers longer in dolines, and some may hold seasonal ponds after heavy rain.

Scientific Importance

Durmitor’s doline fields are internationally recognized as some of the densest and best-preserved in the Dinarides. They provide a natural laboratory for:

• Geomorphology: Understanding karst development and glaciokarst interactions.
• Hydrology: Studying recharge of karst aquifers.
• Climate change research: Dolines serve as cold-air traps, recording microclimatic variations.
• Ecology: Preserving refuges for flora and fauna.

Your Tasks (Field Logging Requirements)

To log this EarthCache, please complete the following tasks at the site:

1. Measure and describe a doline – Estimate its diameter and depth (by pacing or visual estimation) and describe its shape (bowl, cone, collapse, irregular). Explain briefly which process you think contributed most to its formation.
2. Observe hydrology and ecology – Look for evidence of water infiltration (e.g., a ponor, wet ground, seasonal pond) or vegetation differences inside the doline compared to the surrounding terrain. Describe what you see.
3. Interpret the interaction of processes – Based on your observation, explain how both dissolution (karst) and glacial modification might have acted upon this doline.
4. Compulsory photo – Take a picture of yourself (or a personal item, GPS, or notebook) at the rim of the doline, with the depression visible in the background.

Logging Guidelines

• Your answers should be sent to the cache owner before logging online.
• Photos should not reveal answers but should confirm your presence at the site.
• Please respect nature: do not throw objects into dolines, do not collect rocks, and follow park regulations.

Conclusion

Dolines in Durmitor are more than just “holes in the ground.” They are the most characteristic signatures of karstification, shaped here in exceptional numbers and clarity. Their morphology, hydrology, and ecological role make them essential features of the Durmitor landscape and a world-class example of karst science. Visiting them offers not only a geological lesson but also a profound encounter with one of the most unique mountain environments of the Balkans.