17 July, 2008

Pestera Ursilor - a karst cave

As promised here is a short road-side geology from Romania. After arriving in Bucharest we went by train to Cluj-Napoca. I was short of making the train stop while crossing the Carpathians because there were so lovely successions of layered and folded sediments and slight metamorphic rocks that would make any geo cry when not being able to touch and feel them. Anyways, from Cluj a friend drove us to Chiscau in the Bihor mountains where we stayed for some days for hiking. Too bad really that hiking routes were in such a horrible condition that it was impossible to hike to some of the major attractions of the Apuseni mountains. So we were stuck without a car (our friend couldn't stay with his car).

Still we had a nice day with visiting the Pestera Ursilor (the Bear Cave), the largest and best developed showcave of Romania. Approximately 1.100 to 1.500m long it is situated at the end of the Chiscau village in the Magura Hill. Up to 140 skeletons of cave bears have been found in this cave after its discovery during quarrying works at the end of the 1970ties - hence the name.

A set of faults and joints criss-cross the recrystalised limestone of Upper Jurassic age that can by all means be classified as marble (of course a took lose rock as sample/souvenir from the outside). The cave obviously developed along these cracks and formed two over-lapping tube like halls. The upper one is accessible for visits. The cave is a wonderful example of spectacular endokarst with the corresponding features on the surface of exokarst and close-by dolines and other dissolution features of karst.

The formation of the cave likely started during the Pleistocene when it also experienced the major steps of its formation. During the Holocene only minor changes occured and the modern configuration finally developed. The cave tunnel that can be up to 40m (it is hard to make guessing in bad light but i think it is reasonable) in diameter features a wide array of stalagmites, stalagtites, pillars, curtains and more of white to rust brown (seldom) re-precipated calcite.

The formation of these cave features is basicly pretty simple as acidic (CO2!) water percolates through the overlying soil and rocks dissolving a bit of it. When reaching the air filled cave a little Ca is precipated by loss of partiall CO2 pressure. The air in caves normally has a similar CO2 content as the atmosphere, the water coming through the soil and rocks has the CO2 content of those which is usually higher. To reach a balance CO2 is lost from the water to the cave air which results in a lower ability of dissolving Ca - it precipates and all the nice features we are all familiar with form. Gunnar has a nice grafic and chemical explaination on his Blog.

Now some pictures:

A series of spectacular stalagmites and stalagtites together with other cave features.

These look like a forrest of candles, no?

A doline on the other side of the Magura Hill. A bit tricky to recognise due to the dense vegetation.

The view across the Sighistel Valley that also has karst caves to be visited. Sadly the hiking trail ended in the middle of nowhere/Jungle and lacking heavy equipment like a machete we had to turn back.

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