The reason why Volcanism Volcanic Activity increases during low solar activity and minimums

High solar activity "mixes" the core of the earth.  When you have a pot overboiling, a great way to stop it is to stir it.  This is similar to how high solar activity reduces volcanic activity.  The magnetic flux from the sun stirs the magma and perhaps plasma around the core of the earth to keep it from boiling over.  When solar activity is low, the boil-over happens and volcanism is the result and earthquakes as well.