 Also, the timing of volcanism corresponds to shifts of plate motion and changes in the locus of volcanism along the Pemberton and Garibaldi volcanic belts.This brief interval of plate motion adjustment at about 3.5 million years ago may have triggered the generation of basaltic magma along the descending plate edge.Because the Alert Bay Volcanic Belt has not been active for at least 3.5 million years, volcanism in the Alert Bay Volcanic Belt is probably extinct.