Adjoining Galway Bay to the north, the Burren Plateau (Burren is Gaelic for “stony place”) is an example of karst terrain. Karst terrain is generally formed when sedimentary rocks are dissolved by groundwater. This astronaut photograph illustrates the northwestern-most portion of the Burren Plateau, which is characterized by the distinctive bare exposures of almost horizontal, layered Paleozoic-age limestone rocks that form Gleninagh Mountain.
The mountain (image center) appears light gray, with brown concentric banding. Slieve Elva (lower left) is capped with younger dark brown shale, and it has a border of dark green vegetation; at 345 meters above sea level (1,132 feet), it is the highest point on the plateau. The rounded character of limestone hills and intervening valleys of Gleninagh Mountain comes not only from the erosion of the limestone by water, but also from the scouring of loose material by past glaciers.
Most karst occurs in limestones or dolostones, rocks made primarily from the minerals calcite or dolomite. Groundwater and surface water moves through fractures in the rock, dissolving it over time, forming voids and channels. As the voids grow and connect, the rock dissolves even more; when the rock below can no longer support the overlying rock and soil, collapse features like sinkholes form. Over time, the collapses can turn an originally flat landscape into one with significant topography.
A very thin cloud cover is visible over Gleninagh Mountain. Despite the barren appearance of this portion of the Burren Plateau, thin soils are present and the area is used for grazing cattle during the winter. Numerous small springs —another hallmark of karst terrain: surface streams tend to disappear underground via fractures—provide water for both cattle and human use in this otherwise dry landscape.