<P> Tufa columns are an unusual form of tufa typically associated with saline lakes . They are distinct from most tufa deposits in that they lack any significant macrophyte component; this is due to the salinity excluding mesophilic organisms . Some tufa columns may actually form from hot - springs and therefore actually be a form of travertine . It is generally thought that such features form from CaCO precipitated when carbonate rich source waters emerge into alkaline soda lakes . They have also been found in marine settings in the Ikka fjord of Greenland where the Ikaite columns can reach up to 18 m (59 ft) in height . </P> <P> Tufa deposits form an important habitat for a diverse flora . Bryophytes (non-vascular land plants) and diatoms are well represented . The porosity of the deposits creates a wet habitat ideal for these plants . </P> <P> Modern tufa is formed from alkaline waters, supersaturated with calcite . On emergence, waters degas CO due to the lower atmospheric pCO (see partial pressure), resulting in an increase in pH . Since carbonate solubility decreases with increased pH, precipitation is induced . Supersaturation may be enhanced by factors leading to a reduction in pCO, for example increased air - water interactions at waterfalls may be important, as may photosynthesis . </P> <P> Recently it has been demonstrated that microbially induced precipitation may be more important than physico - chemical precipitation . Pedley et al. (2009) showed with flume experiments that precipitation does not occur unless a biofilm is present, despite supersaturation . </P>

Tufa towers in mono lake form by the process of