ABSTRACT
Simms (2002) identified a series of karst forms around the shores of Irish lakes that had a very specific distribution. The rohrenkarren or tube karren are vertical upwardtapering, closed tubes. In a detailed study of the distribution of these forms Simms found that the three lakes he used in his study, Lough Carra, Lough Corrib and Lough Mask, all shared a common feature: all were in a near-permanent state of carbonate saturation. At all three active precipitation of carbonate, as exhibited on the encrustation of plant stems and mollusc shells, was observed. Lakes that were significantly undersaturated did not show any tube karren formation. This means that carbonate saturation is a necessary condition for tube karren formation. The absence of this state means that this karst form will not be produced whatever the other favourable conditions for its formation. Identification of this necessary condition relied upon knowledge of the saturated state of other similar lakes, such as the Killarney lakes of County Kerry. Saturation was not itself, however, a sufficient condition for the formation of tube karren. There needs to be a set of sufficient conditions as well, conditions that produce the form.
