The tongue was there to begin with because Thwaites Glacier is a fast moving one, as glaciers go. That means if you built a cabin on the glacier nine miles inland, in five years it would be ocean front property. This huge mass of ice just flows out on to the continental shelf. The inland part probably floats, but by the time the iceberg tongue got to its mapped position, its northern part at least was aground. That is well over your boots.
Nobody really knows, although lots of people have opinions.
That's part of what the Nathaniel B. Palmer is down here to find out. Where the Thwaites Iceberg Tongue used to be, there is now an area of fast ice. We are following the western edge of this multi year ice north, taking cores, doing CTDs, counting seals, and studying snow as we go. It's fast meaning stuck, not fast zoom zoom. They are probably grounded where Thwaites Iceberg Tongue used to be.