[aerohead]

Volcanic activity can be triggered by earthquake seismicity,which is triggered by a stress relief and tectonic movement following the rupture of asperities within a fault network,all a consequence of plate subduction .
Water migration into a magma chamber can also trigger an explosive volcanic eruption.Magma can just melt a volcanic plug and allow magma to again flow.
The Earth dynamo and magnetosphere is considered a function of convection in the mantle (like a lava lamp).
It looks like the telluric currents occur within the lithosphere,underground and are affected by the magnetosphere,ionisphere and space weather.
They're also be impacted by the heliosphere in which the magnetosphere is embedded,and the galactosphere, and main group,etc..Everything's connected.