map earth 43k global relief topography gebco model bathymetry 3d plus elevation textures gray ref data visualization grid gdal noaa
topographic ridge mid noaa seafloor tectonic spreading irminger occurs jeffrey hutchings faroe greenland iceland
atlantic ocean floor map tharp marie week but professor bruce heezen columbia technician earth geology
atlantic map north bathymetry ridge mid atlantis 1300 elevation ocean usgs noaa thunderbolts picture forty trillion watts four info faults