The greatest recorded thickness of ice is 4,780 m (15,682 ft; 2.97 miles), as measured by radio echo soundings from a US Antarctic research aircraft at 69ø56’17. In addition, on 4 January 1975, a team of seismologists measured the depth of ice in Wilkes Land, in eastern Antarctica, to be 4,776 m (15,669 ft; 2.96 miles) deep.