Limiting volcanism to certain points on an exomoon

I have an exomoon that orbits close enough to its planet that it has notable geological activity. I would like to limit active volcanoes/geysers/lava lakes/etc. to at most, a couple dozen areas on the surface rather than having them be spread all over the moon like Io's volcanos or exist all over tectonic boundaries.

How could I achieve this?

A couple of theories off the top of my head:

• The crust hasn't fully differentiated yet, so there are different concentrations of elements and minerals in different areas, creating weak spots in the crust through which the pressure can be released.
• The moon has large tectonic plates that grind against each other, but large portions of boundaries are buffered by ice, limiting volcanic activity to areas not buffered by ice.

posted over 8 years ago

emo bob‭

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