Have you ever wondered how internet traffic flies around the world? 99% of it travels through cables under the sea. That’s your internet telephone conversation, your instant messages, your email and your website visits, all making their way beneath the world’s oceans.

The reason is simple: in recent years, data has travelled through fibre optic cables. These are much faster and cheaper than trying to bounce messages off satellites and through the airwaves. But we can’t lay them all across our increasingly congested ground, nor can we realistically build telegraph cables to stretch over the Atlantic Ocean.

The miles and miles of cables, which are roughly the size of a garden hose, carry internet traffic at the speed of light. They can carry so much traffic that fewer than 300 cable systems transport almost all internet traffic around the world.

Where are the cables?

This fascinating, interactive map shows the history behind each cable, and shows all the connections between countries. You can have a browse here.

Image: Surfacing

Some notable examples include what is currently the world’s highest-capacity undersea internet cable: a 5600-mile link between the US and Japan. Aptly named “FASTER”, the cable connects Oregon in the USA with Japan and Taiwan. It’s owned by Google and a consortium of other communications companies. “FASTER is one of just a few hundred submarine cables connecting various parts of the world, which collectively form an important backbone that helps run the Internet,” said Urs Hölze, a Google Executive.

Image: Surfacing

This map shows the cables in one glance.

Image: Submarine Cable Map

The amount of internet traffic

The demand for internet capacity is only going to increase. In the future there will be millions of devices connected to the internet, known as the Internet of Things. Cisco estimates that consumer internet traffic will increase by 26% by 2020.

How do you lay the cables in the first place?

This photograph shows how Google laid its FASTER cable. Installing the cable under the sea requires specially designed ships which can lay anywhere from 100-150km of cable per day. The fibre optic cables are very fragile, so they are surrounded with layers of tubing and steel to prevent damage.

Image: Urs Hölzle / Google

A number of things can damage cables. This shark was filmed attempting to take a bite out of the cable. It’s thought it was attracted to the electromagnetic pulses given off by the cable, as sharks also find prey that way.

There are also more ordinary threats to cables, such as construction projects that damage the cables by accident, or even anchors dropped from boats.

Some worry about more sinister attacks. “Russian submarines and spy ships are aggressively operating near the vital undersea cables that carry almost all global internet communications, raising concerns among some American military and intelligence officials that the Russians might be planning to attack those lines in times of tension or conflict,” explained a recent New York Times piece.

If a cable gets damaged, divers are dispatched to take a look at the damage. The cable is then brought to the surface and fixed.