22-Nov-2008 -- One year of various investigations have been preceding this visit in order to accomplish our goal: taking pictures of the seafloor at the confluence. According to the rules of confluence.org "you must be on the Earth's surface" in order to submit a complete visit. Although it is not clearly stated whether the fluid or solid surface counts, we were inspired to take underwater pictures of the sea floor.
Since Lake Lugano has a water depth of 280 m at 46°N 9°E, this task would not be that simple. Waterproof cameras or watertight underwater housings are not designed for depths of more than 80 m. So I decided to use the same approach that let me successfully take underwater images of 47°N 7°E.
Interestingly, the confluence is one of the very few locations in Switzerland that is below sealevel: with a lake level of 271 m and a depth of 280 m the confluence is at –9 m. This record is only beaten by -79 m seafloor height of the Swiss part of Lake Maggiore (lake level 193 m).
The idea was to use the "interval timer" functionality which is a mode where the camera automatically takes a picture every minute. In order to keep my camera dry, I wanted to put it in a preserving jar and let it down to the lake-floor using a self-made uncoiler and a 300 m long line. It was necessary to automatically enforce the flash, because there is not much sunlight left. The flash however gets partially reflected by the glass - thereby degrading the quality of the images. A ring of modelling clay around the object lens prevented those reflections to influence the pictures. Some tests in 12 m depth in a lake near my home have been promising – but I had not yet tried this set-up at such a great depth.
We started the day before (Friday evening) in Zurich. Our train took 3 hours to Lugano, where we stayed the night. The next day I was supposed to hold a presentation at the Swiss Geoscience Meeting. Since my talk was scheduled in the afternoon, we had some time in the morning for attempting the confluence. At 9:30 a.m. we met Silvio Mascetti who owns a boat rental in Lugano-Cassarate. There was a strong wind blowing over the lake that worried Silvio – in particular renting out a boat for two greenhorns like us. So he spontaneously offered to join us and navigate his boat to the confluence himself. With speeds around 30 - 40 km/h we reached the confluence within less than 10 minutes. Obtaining an exact zero-reading at the GPS receiver turned out to be quite challenging due to the storm.
Then the exciting moment had come to let our "preserved" camera down into the water. Luckily Elionora insisted to try first without the precious camera and use some weights instead. The jar with some stones sank down slowly and it took 10 minutes until I could feel that it had reached the ground. Since I had only a total line length of 300 m and the lake being 280 m deep, I had only 20 m residual line left – that required Silvio to keep the boat within 24 m distance from the confluence (according to Pythagoras). Now I began to recover the jar. It turned out to be a difficult process using the self-made bobbin. Once, the string almost got into the ship’s propeller, but we luckily could prevent an accident. Finally, the jar appeared… to our disappointment totally broken with only some residual pieces left on the line.
This is the lesson we learned: a preserving-jar is not made to stand a fluid pressure of 30 bar (3000 kPa). At 300 m depth it simply implodes. For the next attempt the idea would be to use an open container with a bell shaped top. The camera in the top should stay dry while the air inside would be condensed according to the water-depth. However, I would need 30 times the volume of air in order to keep the camera dry this way. This would mean that I have to put on the according weights to compensate the lift. Another idea would be to use a flexible container like a plastic bottle or a plastic bag. Anyone who has an idea is welcome to contact me!
After the experiment was aborted through obvious reasons, we returned ashore and took a scenic walk from Lugano to the Gandria. This village is an old car-free place just 600 m from the confluence. We enjoyed a walk through the Italian-style alleys. On the way back we found almost transparent persimmon (kaki) fruits on the trees.
CP visit details:
- Time at the CP: 10:00 – 10:30 am
- Distance by boat: 2.7 km (beeline, from Cassarate)
- Riding time: 10 min
- Hiking distance: 1.5 km (from Lugano train station)
- Hiking time: 20 min
- Train time: 3 h (from Zurich)
- Distance from lakeshore: 530 m
- Water depth: 280 m
- Distance to Gandria village: 600 m
- Minimal distance according to GPS: 5 m
- Position accuracy at the CP: 5 m
- GPS height: 271 m (water surface), -9 m (lake bottom)
- Weather: alternating sunny, overcast, 8° C
- Description of the CP: In the Switzerland’s most southern canton Ticino, in the central part of Lake Lugano, 530 m from land, in deep water, surrounded by steep rugged rock, earth surface lower than sea level!
- Given Name: The Broken Jar Confluence