Smoo Cave

Smoo Cave is a large combined sea cave and freshwater cave in Durness in Sutherland, Highland, Scotland. GeologySmoo Cave was formed within Early Ordovician dolostones of the Durness Group (also known as the Durness Limestone). The cave has formed along the boundary between the light grey Sangomore Formation and the dark grey, mottled Sailmhor Formation (sometimes called Leopard Rock), both of which form part the Durness Group succession. These horizons close to the formation boundary are characterised by large and abundant chert nodules which can be found all along the inner stream chamber where they have been left behind after dissolution of the surrounding dolostone. The cave was formed along two geological lines of weakness by a combination of erosion from the sea and an inland underground stream which has formed the innermost chambers. Upstream of the Allt Smoo which runs into the cave, impermeable quartzites have been faulted against the Durness Limestone, causing the stream to sink down into the carbonate rock soon after it has crossed the contact between the two different rock types. Physical descriptionThe cave is unique within the UK in that the first chamber has been formed by the action of the sea, whereas the inner chambers are freshwater passages, formed from rainwater dissolving the carbonate dolostones. Partway through the cave the waters of Allt Smoo also drop in as a 20m high waterfall. This is mainly due to the nearby dolostone - quartzite geological boundary where the Allt Smoo stream crosses the impermeable quartzites and sinks on meeting the permeable dolostones. Essentially the cave can be thought of as two caves formed by different mechanisms which have joined together over time. The cave is composed of three main sections; a large sea cave entrance chamber, a waterfall chamber and a short freshwater passage which leads to a terminal sump chamber with some interesting flowstone formations at the rear.

Smoo Cave is a large combined sea cave and freshwater cave in Durness in Sutherland, Highland, Scotland. GeologySmoo Cave was formed within Early Ordovician dolostones of the Durness Group (also known as the Durness Limestone). The cave has formed along the boundary between the light grey Sangomore Formation and the dark grey, mottled Sailmhor Formation (sometimes called Leopard Rock), both of which form part the Durness Group succession. These horizons close to the formation boundary are characterised by large and abundant chert nodules which can be found all along the inner stream chamber where they have been left behind after dissolution of the surrounding dolostone. The cave was formed along two geological lines of weakness by a combination of erosion from the sea and an inland underground stream which has formed the innermost chambers. Upstream of the Allt Smoo which runs into the cave, impermeable quartzites have been faulted against the Durness Limestone, causing the stream to sink down into the carbonate rock soon after it has crossed the contact between the two different rock types. Physical descriptionThe cave is unique within the UK in that the first chamber has been formed by the action of the sea, whereas the inner chambers are freshwater passages, formed from rainwater dissolving the carbonate dolostones. Partway through the cave the waters of Allt Smoo also drop in as a 20m high waterfall. This is mainly due to the nearby dolostone - quartzite geological boundary where the Allt Smoo stream crosses the impermeable quartzites and sinks on meeting the permeable dolostones. Essentially the cave can be thought of as two caves formed by different mechanisms which have joined together over time. The cave is composed of three main sections; a large sea cave entrance chamber, a waterfall chamber and a short freshwater passage which leads to a terminal sump chamber with some interesting flowstone formations at the rear.