  We present a fluid dynamics video on cavities created by explosions of
firecrackers at the water free surface. We use three types of firecrackers
containing 1, 1.3 and 5 g of flash powder. The firecrackers are held with their
center at the surface of water in a cubic meter pool. The movies are recorded
from the side with a high-speed video camera. Without confinement the explosion
produces an hemispherical cavity. Right after the explosion this cavity grows
isotropically, the bottom then stops while the sides continue to expand. In the
next phase the bottom of the cavity accelerates backwards to the surface.
During this phase the convergence of the flow creates a central jet that rises
above the free surface. In the last part of the video the explosion is confined
in a vertical open tube made of glass and of centimetric diameter. The
explosion creates a cylindrical cavity that develops towards the free end of
the tube. Depending on the charge, the cavity can either stop inside the tube
or at its exit, but never escapes.
