  Based on our high resolution, two-dimensional hydrodynamical simulations, we
propose that large cavities may be formed by the nonlinear development of the
combined thermal and gravitational instabilities, without need for stellar
energy injection in a galaxy modeling the Large Magellanic Clouds (LMC). Our
numerical model of the star formation allows us to follow the evolution of the
blastwaves due to supernovae in the inhomogeous, multi-phase, and
turbulent-like media self-consistently. Formation of kpc-scale inhomogeneity,
such as cavities, observed HI map of the LMC, is suppressed by frequent
supernovae (average supernova rate for the whole disk is ~0.001/yr). However
the supernova explosions are necessary for the hot component (T_g > 10^{6-7}
K). Position-velocity maps show that kpc-scale shells/arcs formed through the
nonlinear evolution in a model without stellar energy feedback has similar
kinematics to explosional phenomena, such as supernovae. We also find that
dense clumps and filamentary structure are formed due to a natural consequence
of the non-linear evolution of the multi-phage ISM. Although the ISM in a small
scale looks turbulent-like and transient, the global structure of the ISM is
quasi-stable. We compare the observations of HI and molecular gas of the LMC
with the numerically obtained HI and CO map. The morphology and statistical
properties of the numerical HI and CO maps are discussed.
