Waiting for the Big One: a new class of soft gamma-ray repeater outbursts?

It is suggested that magnetars eventually become unstable to a dynamic overturning instability that destroys most of their dipole moment in a single event. It is further suggested that such an instability would produce a supergiant version of the largest soft gamma-ray bursts that have thus far been observed, and that they could be observed out to tens or even 10(2) Mpc. Persistent emission and afterglows from the fireball might confirm positive identification with nearby galaxies and perhaps provide other distinguishing features as well.