The New Scientist publish an article about some geologists predicting that as the planet warms there will be more eruptions.
My take on that is that it logically follows. If you think globally the rocks in the crust are analogous to toffee. As it warms, it is more pliable. And 1.5° C may seem miniscule but on what scale? Globally.

More pliable, more movement, more magma coming to the surface. If you think the increase is immeasurable - watch this space.