We study ponderomotive effects induced by the electromagnetic ion cyclotron (EMIC) waves in the Pc1 frequency band (0.2 to 5.0 Hz) in a two-ion (H+ and one heavy ion, e.g., He+) plasma. Near the dayside boundary of the magnetosphere, the ponderomotive forces lead to a noticeable accumulation of cold plasma along the field line in two regions of minimum magnetic field intensity located symmetrically around the equator. In the inner magnetosphere, one maximum of cold plasma at the equator is found. At frequencies less than the heavy ion gyrofrequency, the accumulation of cold plasma increases with increasing heavy ion concentration. At frequencies above the heavy ion gyrofrequency, the ponderomotive forces due to EMIC waves are enhanced because of a resonance at the stop band frequencies. We investigate the stop band structure of EMIC waves in a nondipolar magnetosphere and discuss the properties of wave propagation along the field line for different heavy ion plasma concentrations. ¿ 1998 American Geophysical Union