Speleology in Romania - Frasin Aven

Speleology is what got me into geosciences in the first place, therefore a series of posts on caves of all sorts in Romania is in order.
An aven in caving is a very steep or vertical section in a cave that needs ladders or ropes to ascend  and descend. The Frasin Aven (link in Romanian) is located in the Obcina Mare Mountains, which are part of the Eastern Carpathians mountain range.

The Frasin Aven is the northern-most pin on this map; zoom out for better viewing.  Locations of other caves in Romania are also indicated on the map.
View Romanian caves in a larger map


The Frasin Aven can be accessed from Frasin village, on the National Highway #71, between Gura Humorului and Campulung Moldovenesc. The aven was discovered in 1975, it has an elevation change of 73.2 meters, which placed it in the 20th place in the world for elevation change for sandstone caves (based on 1989 statistics).

Frasin Aven sketch, after Giurgiu and Muraru, 1977

From a geologic point of view, the aven is located in the Carpathian Fold and Thrust Belt (Tarcau Nappe), and it is developed in Kliwa Sandstone Formation (Oligocene in age). Kliwa is a deep-water siliceous sandstone (98% silica content), and the aven is thought to have formed within a fracture caused either by extension associated with its position on a crest of an anticline, or via detachment and sliding of the sandstone block along its basal contact (the Kliwa Formation consists of a succession of interbedded sandstone and mudstone).