The breakup of ice shelves has been widely regarded as an indicator of
climate change(1), with observations around the Antarctic Peninsula h
aving shown a pattern of gradual retreat, associated with regional atm
ospheric warming-and increased summer melt and fracturing processes(2-
9). The rapid collapse of the northernmost section of tile Larsen Ice
Shelf (Larsen A), over a few days in January 1995, indicated that, aft
er retreat beyond a critical limit, ice shelves may disintegrate rapid
ly. Here we use a finite-element numerical model that treats ice as a
continuum without fracture(10) to examine the breakup history(2) betwe
en 1986 and 1997 of the two northern sections of Larsen Ice Shelf (Lar
sen A and Larsen B), from which we establish stability criteria for ic
e shelves. Analysis of various ice-shelf configurations reveals charac
teristic patterns in the strain rates near the ice front which we use
to describe the stability of the ice shelf. On Larsen A, only the init
ial and final ice-front configurations show a stable pattern. Larsen B
at present exhibits a stable pattern, hut if the ice front were to re
treat by a further Few kilometres, it too is Likely to enter an irreve
rsible retreat phase.