When a river enters a karst landscape, it can disappear underground through grikes. The grikes become enlarged, forming big vertical holes known as swallow holes. Swallow holes vary in size depending on how large or small the river flowing into them is. Poll na gColm is an example of a swallow hole in the Burren.
Rivers can disappear underground through a swallow hole and re-emerge at some point further downstream
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In pairs, look at this OS map of the Burren. Can you identify places on the map where swallow holes might exist?
