  We have performed stability analysis of axisymmetric accretion mounds on
neutron stars in High Mass X-ray Binaries (HMXB) by 2-D MHD simulations with
the PLUTO MHD code. We find that the mounds are stable with respect to
interchange instabilities, but addition of excess mass destabilizes the
equilibria. Our simulations confirm that accretion mounds are unstable with
respect to MHD instabilities beyond a threshold mass. We investigate both
filled and hollow mounds and the for the latter also compute the expected
profile of cyclotron resonance scattering features (CRSF). In comparison to
CRSF from filled mounds reported in our earlier work, hollow mounds display
wider and more complex line profiles.
