  Laser filamentation is responsible for the deposition of a significant part
of the laser pulse energy in the propagation medium. We found that using
terawatt laser pulses and relatively tight focusing conditions in air,
resulting in a bundle of co-propagating multifilaments, more than 60 % of the
pulses energy is transferred to the medium, eventually degrading into heat.
This results in a strong hydrodynamic reaction of air with the generation of
shock waves and associated underdense channels for each short-scale filament.
In the focal zone, where filaments are close to each other, these discrete
channels eventually merge to form a single cylindrical low-density tube over a
$\sim 1 \mu\mathrm{s}$ timescale. We measured the maximum lineic deposited
energy to be more than 1 J/m.
