Divers of the Dark: The Ojamo Mine Part II

The Ojamo mine has been operating as a diving site for about 40 years. Mining was stopped in the middle of the 1960s. The price of lime fell below the break-even point and it was no longer profitable to continue working the mine. As in many similar cases, when work stopped, the mine slowly started to fill up with water.

-- Advertisement --

The best part was that groundwater began to fill the inside of the mine and had to make its way through a thick layer of earth and gravel. After such natural filtration, crystal clear water reached the mine tunnels. The lakes in this area are usually devoid of large mammals and other animals, but in this case perch, pike and crayfish, quickly populated the murky waters around the mine entrance.

The initial exploration of the mines by amateur divers was limited by equipment shortages. Finland was somehow cut off from what was happening among the cave diving community in the rest of Europe and America. Diving was mainly concentrated around the Baltic Sea, and was done by military and professional divers, earning their living by working underwater. They were not interested in exploring the mine area too deeply, and everything was further complicated by equipment prepared with wreck diving in mind.

Everything started to change in the ’90s when the possibility of diving on mixtures appeared and technical diving flourished. Approx. 10 years later first rebreathers started to appear, which were imported from abroad. It was a breakthrough that allowed to start a journey into the depths of the Ojamo tunnels.

Three-dimensional map of the mine by Adrian Peret

During the first expeditions, the area that is today the first level, located at a depth of 28m, was mapped. The largest part of this level is known as the “Pearls”. It is here that 13 large mine halls are connected by narrow passages. As the level was accessible to divers using nitrox mixtures and open circuit diving, it was recognized and mapped quite quickly.

The next step was the level located at a depth of 56m. At the time of its exploration, air was still the most common gas found in diving cylinders. The entire level was only explored within air limits. All dives at that time were seen as unusual and almost crazy. Today, in the age of rebreathers, where closed circuit diving is slowly becoming the new standard, these 2-3 hour dives seem nothing more than simply the norm.

At that time, initial explorations of the level located at 88m were made, but due to the limitations of using the open circuit, it took a few more years and a whole new technology to be able to move on. Only when diving with CCR allowed deep technical dives to be carried out were the horizontal explorations to 88m and another to 138m continued.

Today, the level at a depth of 88m is completely known. Its mapping was completed in 2008. Today all the attention of the explorers of the Ojamo Mine is focused on the level at the depth of 138m. There is still much to be discovered there, and many tunnels are still waiting for their explorers.

Photo: Divers of the Dark

Most of the techniques used during a mine dive, coincide with what we can observe during a dive in natural caves. The dive team follows the map, of course, if the dive is not an exploration to fill in the white spots on the mine map. Thanks to the fact that mines usually have some kind of documentation, moving around is not very difficult. It should be remembered, however, that maps and reality can be very different, so it is advisable to keep a distance from old drawings.

The main factor limiting dives in the Ojamo has always been the icy water. The prevailing temperature of around 4°C makes any dive lasting longer than 3 hours quite challenging. Fortunately, electric heating and the possibility of creating a habitat make things a lot easier and help to remove some of the limitations. But even today, diving for 5-6 hours can be a real torture, not to mention that something can always go wrong with the suit.

There are no currents in the mine, and visibility in the deeper parts of the tunnels is almost always sensational. Water closer to the surface… well that’s another story. In summer there is darkness all the time. Visibility drops to 1m and sometimes it is even less. Even though the decompression time is spent in warmer water, due to the drastically poor visibility, you have to focus on other challenges.

As in natural caves, there is no shortage of silt and sediment. Due to the lack of current, in sections that have never been explored before, there is a high probability of the water being stirred up by the sediment. Bubbles of exhaled air are sufficient for this.

In the old days, all work was done by hand – Photo: Divers of the Dark

On our way through the tunnels of the Ojamo mine we come across a whole lot of traces of human activity. Mining tools left at the place where work has stopped. The tracks and carriages, on the other hand, look as if they were waiting for the next load to be transported to the surface. At a depth of 138m nothing has been touched since the mine closed. A layer of sediment covers everything, but you can still make out most of the details without any problems.

The light bulbs hanging from the ceiling seem to be waiting for another day to illuminate the miners’ work area again. The pickaxes and hammers left in their places seem to be still waiting for their users, and the neatly stacked boxes of dynamite look as if they were left there only yesterday.

Trees still stand in the outer basin. In winter, when everything is covered with ice, a wonderful festival of sunlight is waiting for the divers, penetrating from the surface into the depths of the water. Flying through the trees on a diving scooter means that decompression does not have to be long and boring.

Source: text prepared with permission and based on materials from the Finnish Cave Divers Group Divers of the Dark