Figure 2 . Development of two rifts that led to the 2017 calving
event. a . Long and transverse fractures formed between Kenyon
Peninsula and Gipps Ice Rise, delineated from the 1963 DISP imagery.b . The locations of R1 and R2 on the 1988 Landsat imagery. The
cyan line corresponds to L2 in panel a . c . The
locations of R1 and R2 on the 2010 PALSAR imagery, showing the widening
of R2 and the propagation of R1 (from points A’ to A and B’ to B).d . The propagation of R1 from 2010 to 2017. e . The
widening of R2 between 1988 and 2017 following the 1986 calving event
that occurred at the southern ice front.
4.3 Temporal variability of flow velocity during 1963–2020
The earliest flow velocities were derived from the 1963 DISP imagery and
the Landsat imagery acquired in 1986 and 1988. Since the available
images for 1986 cannot fully cover Larsen C, we used the 1988 imagery to
fill the data gaps. We also derived the 1986–1988 flow velocities for
the area where both 1986 and 1988 images are available. Due to the
limited resolution of the DISP imagery and the long-time span with the
Landsat data, the flow velocities for this period (1963–1986/1988) are
relatively sparse, and are distributed over the areas with large visible
surface features (Figure 3a). Nevertheless, these velocity measurements
still provide important baseline information for examining the long-term
changes in ice flow. Figure 3b shows the temporal variability of flow
velocity over five areas, including the upstream ice shelf (Area 1), the
northern downstream portion (Area 2), the ice front near Bawden Ice Rise
(Area 3), the central ice shelf (Area 4), and the southern downstream
portion (Area 5). Before 1990, there was no significant velocity change
across Larsen C. On average, the flow velocities after 2000 were higher
compared to the velocities before 1990. Area 1 shows a gradual velocity
increase between 2000 and 2016. Both Area 3 and Area 5 exhibit a step
change in velocity (~50 m/year) between the 2000–2002
and 2008–2010 periods. The acceleration of Area 3 was related to the
northern calving near Bawden Ice Rise in 2004/2005. The acceleration of
Area 5 was concurrent with the rift propagation of R1 during 2006–2010.
The 2017 calving event did not trigger an immediate flow speedup across
the ice shelf.