  During tokamak disruptions the profile of the net parallel current is
observed to flatten on a time scale that is so fast that it must be due to a
fast magnetic reconnection. After a fast magnetic reconnection has broken
magnetic surfaces, a single magnetic field line covers an entire volume and not
just a magnetic surface. The current profile, given by $K\equiv\mu_0j_{||}/B$,
relaxes to a constant within that volume by Alfv\'en waves propagating along
the chaotic magnetic field lines. The time scale for this relaxation determines
the commonly observed disruption phenomena of a current spike and a sudden drop
in the plasma internal inductance. An efficient method for studying this
relaxation is derived, which allows a better understanding of the information
encoded in the current spike and the associated sudden drop in the plasma
internal inductance. Implications for coronal heating are also discussed.
