Icebergs start as land ice—snow that has accumulated on land and, over the course of many years, has been compacted into ice. When this glacial ice flows downstream and reaches the sea, cracks in the ice are widened as warm water and air melt the ice from below and above, respectively. When these cracks become large enough, pieces break off like fingernail clippings and drift into the water as icebergs.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 18.104.22.168.0