Dolinas or torcas: what are, how are they formed, types and examples

Dolinas, also known as torcas in some regions, are circular or elliptical depressions that are formed in the field. They usually appear in areas where soluble rocks predominatesuch as limestone, and can vary in size from a few meters to several hundred meters in diameter and depth.

These structures are common in karst landscapesthat is, those molded by the action of water on soluble rocks. Its appearance can range from soft depressions in the soil to huge craters with steep walls. Some dolinas may contain water, forming small lakes, while others remain dry and act as natural sinks.

Dolinas are formed due to dissolution processes and collapse on land with soluble rocksespecially in karst regions. The water action plays a fundamental role in its origin, since, when infiltrating on the ground, it slowly dissolves the underlying rock, creating underground cavities that, over time, can make the surface collapse.

There are two main types of Dolinas formation:

• DOLINE OF DISSOLUTION: It occurs when rainwater, slightly acidic due to carbon dioxide that absorbs from the atmosphere and the soil, progressively dissolves the limestone or plaster. As the rock dissolves, the terrain sinks slowly, giving rise to soft and progressive depression.
• Collapse Dolina: In this case, the process is more sudden. The dissolution of the rock in the subsoil can generate underground cavities that, over time, lose their ability to withstand the weight of the upper soil. When the structure weakens enough, the ceiling of the cavity yields and collapses, leading to an abrupt sinking on the surface.

In addition to these natural mechanisms, some factors such as Human activity They can accelerate or intensify the formation of dolinas. For example, excessive extraction of groundwater or construction on karst terrain can destabilize the soil and cause unexpected sinking.

Dolinas can be classified according to their origin and appearance. Although all share the characteristic of being depressions in the field, their formation and structure may vary. Let’s see what are the main types of dolinas and their main characteristics listed:

Dolinas of solution

• They form when water progressively dissolves limestone or plaster, creating soft and progressive depression on the surface.
• They are usually wide and shallow, with rounded edges.
• They are common in areas where rainwater or superficial rivers infiltrates the terrain and acts for long periods.

Collapse dolinas

• They are generated when the roof of an underground cavern collapses due to the dissolution of the rock.
• Its formation is sudden and can cause abrupt sinks in the field.
• They have more pronounced edges and vertical walls, with a depth that can reach tens or even hundreds of meters.

Subsidy Dolinas

• They occur when surface material, such as sediments or soft soils, sinks slowly into underground cavities without abrupt collapse.
• They are less dramatic than collapse and develop gradually.
• They usually appear in areas with a layer of clay soil on a dissolved limestone rock base.

Dolinas of fall or erosion

• They are formed when the water drags soil materials into an underground cave, increasing the size of the dolina over time.
• Its process is slow, but can generate large depressions.
• They are associated with areas where there are active groundwater flows.

In this other post you can learn about water erosion: definition, types, causes and consequences.

COLLECTION DOLINAS

• They are depressions in which water accumulates, forming small lakes or ponds.
• They are usually the result of dissolution or collapse dolinas that have been filled with rainwater or underground aquifers.
• Some may become permanent if the water level remains stable.

We will see some of the best known examples of Dolinas in the world.

Great blue hole (Belize)

Located in the Lighthouse reef in Belize, this underwater dolina is approximately 300 meters in diameter and 125 meters deep. It was formed during the last ice age, when the sea level was lower and the area was a limestone cave that collapsed when filling with water.

Discover more about the big blue hole: what is and depth in this other post.

Dolina de Xiaozhai Tiankeng (China)

Known as the “Dragon Sumidero”, it is one of the largest dolinas in the world, with 662 meters deep and 511 meters in diameter. It is located in the province of Chongqing and houses a unique ecosystem inside. Its formation is due to the collapse of a large underground cave.

Bimmah crater (Oman)

This dolina is located on the coast of Oman and is famous for her crystalline turquoise water. It is approximately 50 meters in diameter and 20 meters deep. Although it is popularly believed that it was formed by the impact of a meteorite, it is actually the result of the dissolution of the limestone rock and the collapse of the terrain.

Wolf torca (Spain)

Located in the province of Cuenca, Spain, this Dolina is part of the Natural Park of the Serranía de Cuenca. It is a clear example of the karst action on limestone rock, with steep walls and considerable depth. In the area there are also other similar formations, such as the bride’s torca.

Basel of the swallows (Mexico)

This huge Dolina in San Luis Potosí is one of the deepest in the world, with about 512 meters from its highest point. Its name comes from the birds that inhabit their walls, and is a famous place among rappers and speleology lovers. It was formed by the erosion of water in the limestone rock for thousands of years.

The torcas of the levers (Spain)

The torcas of the levers are a set of Dolinas located in the province of Cuenca, within the Natural Park of the Serranía de Cuenca. It is one of the most impressive karst formations in Spain, with more than 30 dolinas of different sizes and depths that extend in the area.

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