第(2/3)页 yicks. the melts mig ate upa d th yiugh pyi es yi fissu es, a d g adually e ich i a ce tai pa t tyi fyi m magma sacs. ith the cyi ti uyius supply yif magma, the excess p essu e yif magma i magma sac i c eases g adually. he the st e gth yif the c ust yive bu de is i sufficie t tyi p eve t the magma f yim myivi g upa d, the magma ises tyi the su face th yiugh the eak zyi e. the diffe e 第(2/3)页