  We consider front tracking approximate solutions to the p-system of
isentropic gas dynamics. At interaction times, the outgoing wave fronts have
the same strength as in the exact solution of the Riemann problem, but some
error is allowed in their speed. For large BV initial data, we construct
examples showing that the total variation of these approximate solutions can
become arbitrarily large, or even blow up in finite time. This happens even if
the density of the gas remains uniformly positive.
