  The rupture of the thin film at the top of a bubble floating at a liquid-gas
interface leads to the axisymmetric collapse of the bubble cavity. We present
scaling laws for such a cavity collapse, established from experiments conducted
with bubbles spanning a wide range of Bond (${10^{-3}<Bo\leq1}$) and Ohnesorge
numbers (${10^{-3}<Oh<10^{-1}}$), defined with the bubble radius $R$. The
cavity collapse is a capillary-driven process, with a dependency on viscosity
and gravity affecting, respectively, precursory capillary waves on the cavity
boundary, and the static bubble shape. The collapse is characterised by
tangential and normal velocities of the kink, formed by the intersection of the
concave cavity opening after the top thin film rupture, with the convex bubble
cavity boundary. The tangential velocity $U_t$ is constant during the collapse
and is shown to be $U_t=4.5~U_c{\mathcal{W}}_R$, where $U_c$ is the capillary
velocity and ${\mathcal{W}}_R(Oh,Bo)={(1-\sqrt{Oh {\mathscr{L}}} )^{-1/2}}$ is
the wave resistance factor due to the precursory capillary waves, with
$\mathscr{L}(Bo)$ being the path correction of the kink motion. The movement of
the kink in the normal direction is part of the inward shrinkage of the whole
cavity due to the sudden reduction of gas pressure inside the bubble cavity
after the thin film rupture. This normal velocity is shown to scale as $U_c$ in
the equatorial plane, while at the bottom of the cavity
$\overline{U}_{nb}=U_c(Z_c/R)({\mathcal{W}_R}/ {\mathscr{L}})$, where $Z_c(Bo)$
is the static cavity depth. The total volume flux of cavity-filling, which is
entirely contributed by this shrinking, scales as ${Q_T\simeq 2\pi R Z_c U_c}$;
remains a constant throughout the collapse.
