Submarine cables must be resistant to corrosion and abrasion caused by sea currents and waves. In deep waters, they must withstand extremely high pressures. Marine and plant life, too, can pose a serious threat. For instance, on unburied cables forming free spans above the seabed, vegetation can create a hanging curtain which moves with the currents.
Human attack can come from everything from drag anchors to fishing tackle, and that is why cables are ideally buried below the surface.
Finally, submarine cables must withstand great mechanical strain during laying, and ensure the longest possible life to avoid costly recovery and repair procedures