Ms. Koga, we're happy to have you back on our program. First of all, how deep are submarine cables laid?

Let me see. They are laid down at different depths. For example, the deepest part of the submarine cable between Japan and the U.S. is about 8,000 meters below sea level (in the Japan Trench).

8,000 meters... That's a bit hard to imagine.

Mt. Everest is over 8,000 meters high, so the depth is almost equal to that.

Really? The submarine cables are laid down in a deep place like that? Unbelievable! Then, it must be very difficult to lay submarine cables in the ocean.

Yes. It is very difficult. The ocean floor has tall mountains (seamounts), deep valleys, soft muddy areas and hard rugged areas. We need to be careful and make sure that the submarine cable runs on a flat sea bed as much as possible while passing around sunken ships and other obstacles. That's why the preliminary exploration we conduct to decide the route of the submarine cable is very important. We spend a lot of time on the preliminary exploration and carefully decide on the route. But, while exploring these deep parts of the ocean is important, we need to pay attention to shallow sea areas as well.

Shallow sea areas? What are you careful about?

When deciding on the route, we try to avoid precious fish beds and coral reefs in consideration of the environment. Also, if the cable gets caught in the dragnet of a fishing boat or the anchor of a ship, it is dangerous. So, in shallow sea areas, we bury the submarine cable under the sea bed, instead of laying it down on its surface. As another precaution, the diameter of submarine cable used in shallow sea areas are larger than those used in deep sea areas so that the cable won't break if it comes into contact with an obstacle.

That's surprising. I thought cables were larger in deep sea areas because of the pressure of water.