USING LATE BRONZE AGE WALLS AT KALAMIANOS, GREECE, TO DETERMINE A MINIMUM RATE OF RILLENKARREN FORMATION

The Late Bronze Age, Mycenaean site of Kalamianos, located on the coast of the arid Korinthia of Greece, presently receives an average annual rainfall of 371 mm/yr with a mean January temperature of 10.2 C and a July mean of 27.8 C. The site has significant Mesozoic limestone outcrops and a large number of exposed limestone walls that were erected a maximum of 3500 years ago. Solution weathering of limestone surfaces produces rillenkarren, or solution fluting that is weakly developed on walls relative to bedrock. Rillenkarren at the site have been characterized with respect to width, depth, length, slope of surface, radius of curvature and height above ground, with width, depth and surface slope proving to be statistically robust variables applicable to flute evolution. Previous work suggests flutes undergo a two-stage evolution, widening first and then deepening, and that upon reaching dynamic equilibrium flutes do not change shape but their continued growth lowers the rock face.

The most mature rillenkarren at Kalamianos are found on bedrock surface slopes of 40-60 degrees. Bedrock flutes are longer, wider and deeper than wall flutes, with width to depth ratios of approximately 4.5:1 for bedrock and 9:1 for walls. We hypothesize that the larger ratio for walls is due to moderate width development and a lag in depth development – a function of a two-stage evolution.

We determined the minimum rate of evolution for rillenkarren by using a maximum age of 3500 years for Mycenaean walls and the median width and depth of flutes formed at optimal slopes. Though linear rates are unlikely they give us a first approximation for the evolution of the width and depth of wall flutes and we calculate linear rates of 0.257 mm/century and 0.028 mm/century, respectively. We believe that the ten-fold difference in rate is due to the two-step evolution of flutes. Applying these rates to mature bedrock rillenkarren we calculate that bedrock flutes reached dynamic equilibrium a minimum of c. 4400 yrs ago and a maximum of c. 10,000 yrs ago.

Rillenkarren on toppled stone from the Mycenaean walls provides an opportunity to test the rates, and a calculated age of c. 4000 yrs suggests that the rates are on the correct order of magnitude but slightly low, which should be expected since we used the maximum possible wall exposure time to derive our rates.