|Image: Steinerne Rinne near Rohrbach.|
Tufa Runnel is not a scientific term.
Unfortunately we could not find the english term for this rather common and
impresive structure, it seems it has not been described in english literature so
So this is a try to find a descriptive term.
|Image: detail of the top.|
A tufa runnel is a typical formation of tufa or travertine, close to karst
The water from the karst spring is very rich in soluted limestone, which is only
possible because of its high content of carbon dioxide.
But as soon as the water reaches the surface, the carbon dioxide leaves the
water into the air and the limestone is deposited.
Commonly if forms dams, lakes, and huge deposits of tufa.
But in some cases, it the water flows down a certain slope, immediately after
the spring, the water is too fast to form dams.
The tufa is deposited primarly as shoreline tufa along the brook, and also as
The result are two tufa dams along the water, which grow continually forming a
At the same time limestone depositition in the stream bed lifts the brook, and
so after some time the brook has forme a sort of wall, where it rans on top.