  Aims: We investigate the formation of flux ropes in a flux emergence region
and their rise into the outer atmosphere of the Sun.
  Methods: We perform 3D numerical experiments solving the time-dependent and
resistive MHD equations.
  Results: A sub-photospheric twisted flux tube rises from the solar interior
and expands into the corona. A flux rope is formed within the expanding field,
due to shearing and reconnection of field lines at low atmospheric heights. If
the tube emerges into a non-magnetized atmosphere, the flux rope rises, but
remains confined inside the expanding magnetized volume. On the contrary, if
the expanding tube is allowed to reconnect with a preexisting coronal field,
the flux rope experiences a full eruption with a rise profile which is in
qualitative agreement with erupting filaments and Coronal Mass Ejections.
