Chousei Coal Mine is located in Ube City, Yamaguchi Prefecture, Japan, and is part of the Ube Coal Field.
Ube Coal Field is a group of submarine coal mines that are no longer in operation.
In the late 19th century, mining operations in the Ube coal field began in earnest with the opening of a coal bureau by the Yamaguchi clan, and British engineer Maurice was invited from Nagasaki to operate the mines with the introduction of Western-style coal mining technology.
After the Meiji Restoration, management of the Ube coal mines was transferred to the private sector in 1872, and a number of coal mines were opened during this period as demand increased due to the Sino-Japanese War.
The mining of the seabed was introduced in the Ube Coalfield after 1912, and it is said that the amount of coal produced in the Ube Coalfield doubled after that time.
The Ube coalfield did not continue to operate peacefully, and several major seawater inflows occurred.
Although operations continued to be affected by the increase and decrease in demand due to the war, all coal mines in Ube City closed in 1967 due to the gradual shift to oil as the main energy source after World War II.
The coal mine where the seawater inflow accident occurred could not be rescued or the bodies salvaged, and the entire mine shaft was abandoned.
Therefore, the bodies and relics left in the submerged mine shafts were left untouched.
The chousei coal mine is one of the Ube coal mines that experienced a flooding accident in 1942 that resulted in the deaths of 183 people.
Note that 137 of the 183 victims of the Chousei Coal Mine accident were from the Korean peninsula.
It is reported that there were more Korean workers in the Ube Coal Mine than in other areas of Ube coal field.
It is estimated that about 40% of the total workers in the Ube coalfield were foreign workers, and about 85% of these foreign workers were from the Korean Peninsula.
The existence of coercion against foreign workers and the quality of the work environment are disputed in some cases, but we will not discuss those issues here.
In any case, the fact remains that 183 bodies were left in the submerged coal mine.
Piers are the exhaust and drainage stacks of the tunnels.
The original entrance to the Chousei Coal Mine has been reclaimed and we are attempting to enter the underwater mine from the peir.
Of course, we also have in mind to dig back the original entrance.
The piers protrude about 5 to 7 meters above sea level, and the water surface inside the piers is approximately the same height as sea level, but seems to be slightly higher than sea level.
We began our research and exploration of the site in July 2024.
During the initial survey, we tried to enter the pier of offshore side (called offshore pier), but we were unable to enter the pier due to high waves caused by a typhoon a few days before the survey date, which prevented us from working to build scaffolding to enter the inside of the pier.
During the second survey, we were able to enter the offshore peewee of the two piers.
When we went underwater, the transparency deteriorated to about 50 cm from a depth of about 7 meters.
The water inside the peir appeared to be almost entirely freshwater.
Diving through the interior structures, we found a pile of broken pipes and scaffolding at a depth of around 27 meters.
The temperature at the bottom of the water was 18 degrees Celsius, and since the seawater temperature was 22 degrees Celsius at this time, there appeared to be little or no seawater in the mix.
According to the drawings, the entrance to the tunnel was located at that depth, so we searched along the inner wall of the peir but could not find the entrance due to the piles of objects.
The next survey will be conducted in the shore peers where the drawings show no such piping, etc.
If we are still unable to enter the tunnel, there is a possibility that salvage work of the broken piping will be conducted.
We attempted to excavate the entrance to the mine, which had been reclaimed at the time of the accident 80+ years ago.
Fortunately, drawings and other documents from the period when the mine was in operation remain, and the general location of the mine entrance can be determined.
We began excavation work with heavy equipment on September 24.
We were unable to excavate the entrance to the tunnel on the day we began construction, but fortunately again, we were able to find the entrance to the reclaimed tunnel the following day, September 25, 2024.
The cost of these excavations was funded by crowdfunding.
Water trapped for more than 80 years began to overflow from the entrance of the mine.
The frame of the tunnel was made of pine wood, and the entrance section was 2.2 meters wide and 1.6 meters high.
The water surface rises and falls with the ebb and flow, indicating that there is some kind of traffic with the ocean. However, upon confirmation, the water was freshwater, there are no large holes in the sea.
We spent several days there, clearing the ground and taking certain measures to prevent the surrounding soil from sloughing off. We also paved the pathway to the entrance of the mine with concrete.
After the land clearing, a memorial ceremony was held by the civic orgnization on October 26, 2024 with the families and relatives of the victims of the collapsed coal mine.
We conducted our second dive survey at the end of October.
On October 29, we conducted a dive from the peir closer to shore(called shore pier), and on October 30, from the entrance of the mine.
In the previous survey we used an open circuit for simplicity, but this time we used a closed circuit to reduce the risk of collapse because of the high possibility of getting more inside the mine.
This is because it is assumed that the breathing bubbles will contribute to the collapse, and in the long term, the oxygen in the exhaled air will degrade the tunnel frames.
According to a survey conducted in the 1980s, there is a history of being able to descend to the very bottom because there was little piping or other obstructions inside the shore pier, so there was hope that it would be possible to enter the interior of the mine from shore pier in addition to the entrance of the mine.
We prepared our equipment on the morning of the 29th and attempted to dive to pier in the afternoon.
The pier on shore is about 6 meters high, and we had hooked rope ladders to the outer and inner walls in advance so that we could ascend and descend.
The waves were high that day, and it took some time to get to the shore pier, but we reached them safely and succeeded in getting inside the pier.
When inside the shore pier, the water was murkier than offshore peers and did not provide much of a field of view.
The visibility was clear enough to see one's hand down to a depth of about 5 meters, but below that depth, the visibility was 10 cm or less.
We descended to a depth of about 23 m, but could not reach the very bottom because of obstructions by broken steel pipes and other internal structures.
We groped around for a route, but we decided that it would be difficult to continue the survey from the shore pier and decided to cut off the dive after about 10 minutes.
On October 30, a survey was conducted from the entrance to the main tunnel which was thought to offer the best possibility of access to the inside of the mine.
A large number of press gathered to interview the survey on October 30th, we began the dive surrounded by more reporters than ever before.
We had expected the water to be a bit clearer as we went deeper, but the clarity was about 10 cm all the way.
Although there were only a few moments when there was enough visibility to see own hands, we were able to get in to the point where we we used up one of our reels.
Using a different reel, we continued on a little further, and although it looked like we could still go further, we decided to turn back this time because we were about to reach our scheduled dive time.
The depth at which we decided to turn back was 26.1 meters, and we were able to almost reach the very bottom which is estimated to be about 30 meters.
In addition, the water temperature was about 18 degrees Celsius, all fresh water, and the slope angle was about 10-15 degrees.
Since we think the skeletal remains are located near the bottom area, we believe that there is a high possibility that we will be able to actually recover the remains next time.
Copyright © 2024 Japan Karst & Underwater Exploration Project