Karst - an introduction

Karst is a landscape with distinctive hydrology and landforms that arise when the underlying rock is soluble. The vast majority of karst landforms are found on carbonate rocks, such as limestones. Karst landscapes typically are characterised by distinctive features including sinkholes, caves, enclosed depressions, disappearing streams, springs and sinkholes. Karst aquifers, which are karst rock that can provide drinking water, contribute substantially to freshwater supplies in many regions of the world. The World Karst Aquifer Mapping (WOKAM) project has created a world map and database of karst aquifers as shown below. You can see in the map below that over 20% of the European land surface is characterised by the presence of carbonate rocks and about 14% of the land surface is carbonate rock outcrop (rock is at the ground surface with no soil on top).

In Ireland we have a large proportion of carboniferous limestone rock present particularly across the midlands and the west of the country. Karst features have been located in nearly every part of Ireland meaning that most of our pure limestones have undergone some form of previous karstification. We have both upland (like the Burren) and low-lying areas of karst in Ireland (Gort lowlands). 

Most karst landforms in Ireland are found in the West of Ireland. The nature of the limestone strongly influences its susceptibility to karstification. Pure bedded limestones are more susceptible to karstification and contain most karst landforms than impure (or mud or shale-rich) limestones. 

The Main karst regions are:

• The Burren Plateau
• Plateaux of the North-West
• The Western Lowlands
• The Eastern Lowlands
• Southern Valley Karst

Carbonation is one of the most common forms of chemical weathering. Carbon dioxide is absorbed by rainwater as it falls. The rainwater passes through the soil absorbing more carbon dioxide which is released by organic matter. The rainwater and carbon dioxide combine forming a weak carbonic acid which causes a reaction with the calcium carbonate in limestone rocks. This reaction produces a solution called calcium bicarbonate. The solution slowly dissolves the limestone through the process of solution at its lines of weakness in the bedding planes and joints. Limestones with a high calcium carbonate content are known to display the best examples of karst features.

Follow the interactive map below to explore the main karst landform features illustrated above in the diagrams.

Karst hydrology can be very complex as water can be exchanged between the land surface and the bedrock in large volumes and the movement and exchange of water is often difficult to track and quantify. One of the most complex lowland karst hydrological systems is located in south-east Galway across the Gort lowlands. An overview schematic of the main rivers which flow from the upland mountainous area to the east onto the lowland karst on then on to the sea at Kinvara is shown below. Below ground flow of water in the karst bedrock is shown in red dashed lines whilst blue lines represent river flow above ground.

The Slieve Aughty mountains are located to the east and are made up of Old Red Sandstone rock. Three river flow off these mountains onto the Limestone rock of the Gort lowlands and then disappear and reappear a number of times before draining to the sea at Kinvara completely underground though the bedrock - the last visible surface water feature before Kinavara is Cahermore turlough located almost 6km inland (just north of Caherglassaun in the map below). The geology, main rivers and turloughs in the Gort lowlands are shown in the map below.

Click on the button "Open in Map Viewer" on the map below or alternatively copy and paste the link below in a new tab.

Try turning on and off the bedrock geology and and karst feature map layers for the Gort lowlands.

https://arcg.is/050nH00

Use the interactive map below to follow the complex path of the largest river flowing off the Slieve Aughty Mountains as it flows down onto the Gort lowlands and enters the karst limestone environment.

A Turlough is temporary or seasonal lake that appears during the wettest time of the year in late Autumn or Winter and disappears again in late Spring. Turloughs can be fed either by rivers that drain to a swallow hole that backs up during high flow periods, or by the karst bedrock draining the surrounding area. Sometimes turloughs are filled from locations that are far away, where the bedrock allows water to rise up in low depressions like a surcharge tank. Because of their unusual environmental conditions, turloughs support very special ecosystems which are rich in plants and insects.

In some turloughs, there is a permanent pond or wetland in the middle. In the wintertime, when the water table rises, turloughs turn into lakes. They fill quickly – over a matter of hours or days – either from the inflowing river or usually from the bedrock itself. In the summertime when they are dry, they are typically grasslands, usually grazed by cattle.

Below are they animations of how the three main types of turloughs fill and empty.

In 2007 Polish diver Artur Kozlowski and Irish diver Tom Malone began cave diving in Ireland which is a unique and often dangerous challenge. They began diving in Kiltartan starting in early 2008, and in the face of winter floods and spring storms, the project was named the 'Riders on the Storm' traverse. Over a number of years and facing many obstacles and dangerous near misses, and with the help of many other divers, Arthur and another diver Jim Warny managed to successfully traverse the connection between Castletown and Kiltartan which they believed to be the longest traverse of water-filled underground caves in Ireland and Britain. It took 45 separate dive attempts to complete the traverses totaling 4km. The path of their traverse is marked on the map below and a cross-section of what they encountered is also shown.

Tragically, Artur Kozłowski died during a cave dive in the Gort lowlands on 5 September 2011 - he will always be remembered as an avid explorer and he contributed substantially to our understanding of the caves beneath the Gort lowlands.

The picture below is of a cave diver who is installing an instrument to measure the water level or "water head" at the Kiltartan river sink in 2020 as part of a GSI research project.