  The singularitiy inside a spherical charged black hole, coupled to a
spherical, massless scalar field is studied numerically. The profile of the
characteristic scalar field was taken to be a power of advanced time with an
exponent $\alpha>0$. A critical exponent $\alpha_{\rm crit}$ exists. For
exponents below the critical one ($\alpha<\alpha_{\rm crit}$) the singularity
is a union of spacelike and null sectors, as is also the case for data with
compact support. For exponents greater than the critical one
($\alpha>\alpha_{\rm crit}$) an all-encompassing, spacelike singularity
evolves, which completely blocks the ``tunnel'' inside the black hole,
preventing the use of the black hole as a portal for hyperspace travel.
