The extensive mid-Atlantic ridge is colour-coded in this image for topography. Warm colours (yellow to red) are at higher elevations than the cooler colours (green to blue). The ridge crest increases in elevation toward Iceland, which is thought to be a hotspot underlain by a plume of hot mantle. The hot mantle thus powers abundant volcanism at Iceland and provides thermal bouyancy for the northern ridge segment (courtesy of NOAA). The crest of the mid-oceanic ridge of the south Pacific is apparent in this false-color image dipicting topography. The warm colors (yellow to red) are at higher elevations than the cool colors (blue). The ridge is offset by numerous fracture zones, the most obvious of which occur near the center of the image (courtesy of NOAA).