As evidence, the researchers point to propagating rifts on the top of the ice shelf and basal crevasses beneath it, both of which are visible in the satellite image above, the rifts as diagonal lines and the crevasses as nearly vertical ones. The crevasses arise from basal melting produced by active volcanoes underneath West Antarctica combined with so-called circumpolar deep water warmed by climate change.
However, as Easterbrook explained in response to a 2014 scare about the adjacent Pine Island glacier, this reasoning is badly flawed since a glacier is not restrained by ice at its terminus. Rather, the terminus is established by a balance between ice gains from snow accumulation and losses from melting and iceberg calving. The removal of ice beyond the terminus will not cause unstoppable collapse of either the glacier or the ice sheet behind it.
Other factors are important too, one of which is the source area of Antarctic glaciers. Ice draining into the Thwaites Glacier is shown in the right figure above in dark green, while ice draining into the Pine Island glacier is shown in light green; light and dark blue represent ice draining into the Ross Sea to the south of the two glaciers. The two glaciers between them drain only a relatively small portion of the West Antarctic ice sheet, and the total width of the Thwaites and Pine Island glaciers constitutes only about 170 kilometers (100 miles) of the 4,000 kilometers (2,500) miles of West Antarctic coastline.
Of more importance are possible grounding lines for the glacier terminus. The retreat of the present grounding line doesn’t mean an impending calamity because, as Easterbrook points out, multiple other grounding lines exist. Although the base of much of the West Antarctic ice sheet, including the Thwaites glacier, lies below sea level, there are at least six potential grounding lines above sea level, as depicted in the following figure showing the ice sheet profile. A receding glacier could stabilize at any of these lines, contrary to the claims of the recent research study.
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