  Coronal mass ejections (CMEs) can trigger geomagnetic storms and induce
geoelectric currents that degrade the performance of terrestrial power grid
operations; in particular, CMEs are known for causing large-scale outages in
electrical grids. Submarine internet cables are powered through copper
conductors spanning thousands of kilometers and are vulnerable to damage from
CMEs, raising the possibility of a large-scale and long-lived internet outage.
To better understand the magnitude of these risks, we monitor voltage changes
in the cable power supply of four different transoceanic cables during time
periods of high solar activity. We find a strong correlation between the
strength of the high-frequency geomagnetic field at the landing sites of the
systems and the line voltage change. We also uncover that these two quantities
exhibit a near-linear power law scaling behavior that allows us to estimate the
effects of once-in-a-century CME events. Our findings reveal that long-haul
submarine cables, regardless of their length and orientation, will not be
damaged during a solar superstorm, even one as large as the 1859 Carrington
event.
