  The formation of Mach cones is studied in a full $(3+1)$-dimensional setup of
ultrarelativistic heavy-ion collisions, considering a transverse and
longitudinal expanding medium at Relativistic Heavy-Ion Collider energies. For
smooth initial conditions and central collisions the jet-medium interaction is
investigated using high-energy jets and various values of the ratio of shear
viscosity over entropy density, $\eta/s$. For small viscosities, the formation
of Mach cones is proven, whereas for larger viscosities the characteristic
structures smear out and vanish eventually. The formation of a double-peak
structure both in a single- and in a multiple-jet event is discussed.
