Old ice up to 3 m or more thick that has survived at least two summers' melt. Hummocks are even smoother than in second-year ice and attain a look of mounds and hills. The surface of multiyear ice fields in places not subject to deformations is also hillocky due to non-uniform multiple melting. The ice is almost salt-free. Its color, where bare, is usually blue. As a result of melting, round puddles appear at its surface in summer and a well-developed drainage system is formed.
On behalf of the IHO Member States, the International Hydrographic Bureau would like to thank Korea Hydrographic and
Oceanographic Agency(KHOA) of the Republic of Korea for giving active support in the development of the S-100 GI Registry