22 October 2005

A visit to Dersios 24-25 September 2005

A visit to Dersios 24-25 September 2005

The sink-hole Dersios is located on the Palaiochora plateau at a height of 755m and belongs within the boundary of the municipality of Tyros or Tyrosapounakeika of the Arcadia Prefecture. The distance from Tyros is about 45 minutes on a dirt track.

The sinkhole was first explored by a French team in August 1974 with the participation of ESE - the Hellenic Speleological Society. Since 2001, SELAS Caving club, Greece has been conducting expeditions to Dersios, emptying the first sump in 2003 (doubling the depth and more than tripling the length of the cave). This year expeditions were carried out almost every week from June to the end of September (August excluded). This years perseverant attempts to empty other sumps higher in the cave have allowed the SELAS caving club's teams to explore new undiscovered sections of a length of ~570m.

We got to the cheesevault late on Friday night with Nikos driving and found Komninos already there. Komninos had gathered wood and set a fire in the fireplace. We exchanged stories of lightning strikes and fog during the trip there and prepared for bed.

In the morning the usual orgy of eating took place and we then got the divers' bottles ready for the dive and set off for the entrance.

The divers would go to de-rig the new section and survey the last part of it (in the end, it was 14 stations ~100m), while I went to make the sketch map in the old section and alter the hosepipe position in the first sump ready for winter. All tasks of the day were conducted successfully and Komninos came out to cook and prepare for the return while I stayed behind with Nikos for the sketch map.

After the successful omelet of 10 September we went mad this weekend: two different types of sausage, fried chicken wings (chicken spareparts according to Theodossis), omelets, roasted chestnuts and onions in the ashes. Boy did we eat that weekend!

The second day tasks were Nikos to survey the sump in the first sidebranch. There's a 50m or so continuation a little lower than the route taken in exploration in July. Because it was narrow and kept getting silty, he only managed a few measurements. I carried on the sketch map and at some point in the afternoon Nikos started the de-rigging and we went on together to the exit. I have written elsewhere about the method of our exit.

In addition to survey measurements and the sketch map a rigging chart was drafted as was a list of all foreign objects found inside the sinkhole to try and get a chronological outline of the deposition of items in the cave - and therefore an idea of to what extent the cave gets blocked with water. It needs a little bit of chasing but there may be something useful at the end of it. According to Theodossis, the last time it blocked right up was in 1991. This means that the items found with a more recent terminus ante quem which we find both above and below the first sump made their way in during flow less cataclysmic than total blockage.

Some words about the fauna...

Just like last year at the same time of year we noticed increased Guano in the cave, especially in the large chambers. I don't know what the life cycle of the bats is, or to what extent they follow the seasons, if at all. Chambers 9-12, the "screw" and the little chamber before the first sump are the places where I saw the bats gather - in the first two there is gathered guano from other years while in the last place it was the first time I had noticed bats. Here it seemed to me they were enjoying the new found space in the now empty sump and were diving into it. To judge from the dead bat some way below the first sump, some daring bats had made it across the sump and beyond. I'd like to mention a bat we had found at the highest point while surveying the first sidebranch in 2004. I draw the reader's attention to my other text on the cave mice we had found, to bring the vertebrate description to a close. They haven't been seen again since.

On to the invertebrates: There are these little guys both before and after the first sump. They're about 10mm long, white and diaphanous little critters with plenty of legs underneath. These animals are surely arthropods and quite probably isopods. They have antennae at the front but I did not have an opportunity to sit and write my comments on the spot so I forget the details. The ones in the image show the black line which runs along the full length of the animals - I assume it is the digestive system (the whole animal is diaphanous apart from this part) and seems black most plausibly because the animals in question were found busying themselves on a blackened log just after the first sump.

A little more care next time may help in identification - questions like how many legs they have per section, how many pairs of antennae, and others. Nikos tells me he has spotted cave shrimp in this cave and the chances are that this is them. Let someone correct me if I am wrong.

On to our friends the dolichopodes - which we have seen beyond the first sump but also in great numbers outside the cave at night when coming out. All the ones I have seen have been of medium size - about 40mm long. They aren't so dispersed in the cave, no doubt due to its nature as a sinkhole.

Finally - on Sunday on the way out we found a large number of well fed slugs which must have been about 70mm long and about 15 to 20mm wide at their widest.

I hope next year we will manage to record more details and have the opportunity to photograph the fauna of Dersios a little more clearly,

Some words about the results of this years explorations:

Total length of surveyed sections (30 September 2005): 1.525m
Total length of surveyed sections planimetric development (30 September 2005): 1.392m
Total depth of surveyed section (30 September 2005): 164m
Estimate of explored length (30 September 2005): ~1.800m
Estimate of the explored depth (30 September 2005): ~185m

The equivalent values in April 2005 were:
Total length of surveyed sections (April 2005): 908m
Total length of surveyed sections planimetric development (April 2005): 826m
Total depth of surveyed section (April 2005): 161m
Estimate of explored length (April 2005): ~ 1.100m
Estimate of the explored depth (April 2005): ~185m

This years exploration resulted in a 69% increase in the planimetric length of the cave in relation to last year (566m were added). The surveys have been uploaded to the photos.selas.org site here: my Dersios Album

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