"The runaway occurs because of two weakening mechanisms, thermal weakening
and strain rate weakening. Because of this weakening the stresses are
dramatically reduced (by orders of magnitude) compared with what they would
be without this physics. Because the deformational heating is proportional
to the stress times the strain rate and the stresses are so strongly
reduced,
the heating is not nearly so extreme. The technical details
are spelled out in my papers and these effects are included in my numerical
calculations. They are there for anyone with the technical background to
examine and verify."
Jim