Why does surface area of a reactant influence the rate of the reaction?

A larger surface area increases rate of reaction. This is because when you break up a lump of a substance (either into smaller lumps or a powder) more of the particles are exposed to the reactant particles. This means that collisions are occur more frequently which increases the chances of successful collisions occurring.

That result from subduction of oceanic plates beneath lighter continental plates. most of the earth's volcanoes are located around the pacific ring of fire because that the location of most of the earth's subduction zones.