Fairy chimney erosion rates on Cappadocia ignimbrites, Turkey: Insights from cosmogenic nuclides

Cappadocia, in the Central Anatolian Plateau of Turkey, is famous for its unique landscape and unusual rock formations. The development of this landscape dates back to Late Miocene epoch (c. 10 million years) when volcanoes spread pyroclastic deposits over an area of about 20,000 km2. The volcanism continued for several millions of years and laid down thick and colorful ignimbrite layers. The evolution of the Cappadocian landscape starts with nearly-horizontal plateaus, which are then dissected, usually along cooling fractures, to form mushroom-like structures (hoodoos) locally known as “fairy chimneys”. Different layers of ignimbrites have different resistance to erosion: softer layers (necks) are easier to erode compared to the harder ignimbrites (caps). When the chimneys are isolated, the caps play an important role in slowing further erosion of softer layers. When the caps finally drop or completely erode away, the soft necks of the chimneys are quickly destroyed. Here, for the first time, we have determined the bedrock erosion rates at the three evolution stages of fairy chimneys using the cosmogenic chlorine-36 (36Cl): the pre-chimney (plateaus) stage, the chimney stage and the post-chimney stage. The data show that the plateaus erode at a very low rate between 0.58 ± 0.02 cm/ky and 0.93 ± 0.05 cm/ky. When dissection of a plateau starts, the erosion rate increases to about 4.5 ± 0.6 cm/ky. The caps of chimneys have erosion rates between 3.21 ± 0.36 cm/ky and 3.39 ± 0.36 cm/ky. Once the chimneys disappear, erosion rates increase significantly to 28.0 ± 9.9 cm/ky.