What natural phenomena can affect telluric currents?

Telluric currents are natural currents that occur in the Earth's crust and are primarily influenced by electromagnetic phenomena. Sunspot activity affects telluric currents because it is associated with solar radiation fluctuations that can generate geomagnetic storms and affect the Earth's magnetic field. These geomagnetic effects can induce electric currents in the ground, altering the behavior of telluric currents.

While the other choices may have indirect effects on the environment or geological processes, they do not have the direct electromagnetic influence on telluric currents that sunspot activity does. Earthquakes and volcanic eruptions can cause geological disturbances but do not impact electromagnetic conditions to the same degree. Likewise, ocean currents may affect local electrical properties through thermal effects but are not a primary factor in the generation of telluric currents.