We have studied propagation along magnetic flux tubes in the active-region corona of large-amplitude torsional Alfvén wave packets (TAWP’s) coming up from a subphotospheric convection zone. TAWP’s can serve to transfer magnetic energy from the high-$\beta (\beta = P_{\mathrm{g}}/P_{\mathrm{m}})$ subphotospheric region to the low-$\beta$ coronal region. They dump part (or all) of their energy in the low-$\beta$ coronal region, which may result in very high temperature-plasma observed in X-rays (and in high energy particles). The supply of TAWPs from the photosphere, considered to be inefficient because the Alfvén velocity in the photosphere is small, turns out to be sufficiently effective for large-amplitude TAWP’s. This is due to the magnetic buoyancy acting on the magnetic twist packet and to the non-linear effect of squeezing out the gas from the twisted part of loops when it comes up near the photosphere. Both of these effects enhance the speed of emergence of the twist. We propose that loop flares may be due to the transport of energy and mass by torsional Alfvén waves. They may be the result of energy conversion of the magnetic twists and the kinetic energy of the accelerated hypersonic flows into thermal energy when two such TAWP’s collide high in a coronal loop. In order for such a collision of TAWP’s to occur, a TAWP is injected from one footpoint of a loop whilst another TAWP, from the other footpoint, is still propagating along the loop. The collision of these two TAWP’s at a high part of the loop explains the creation of a hyperhot region. The acceleration of high-energy particles is also explained as being due to the Fermi-I process between the approaching two hypersonic magnetic shocks.