The seafloor remains among the most inaccessible regions of our planet. Even though at least 70% of Earth's surface is composed of oceanic crustal rocks, only a small portion of the global seafloor has been mapped in detail.

However, details of the seafloor bathymetry (depth), structure, and geology began to emerge following World War II as geologists developed a variety of instruments to measure geophysical properties of the Earth. Even today, geophysical measurements at sea provide marine geologists with the best information about geologic processes and phenomena occurring many kilometers beneath the waves.

One interesting feature of the seafloor discovered using geophysical data was the occurrence of long chains of seamounts, especially throughout the Pacific Ocean basin. The image below shows the longest of these chains composed of the Hawai'ian archipelago and a chain of submerged mountains known as the Emperor Seamounts.

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The image was derived from a digital elevation model of a portion of the North Pacific Ocean and rendered using Geographic Information System (GIS) software. The view is looking northward across the central North Pacific Ocean basin. The line of mountains extending from the right-hand corner to the left top of the image is the chain.

The image below is another virtual view of the Hawai'i - Emperor Seamounts, with prominent seamounts labeled. This view looks northwestward along the axis of the Hawai'ian Seamount chain. Hawai'i and the Hawai'ian Islands are located near the bottom of the image. Midway Island and several of the Emperor Seamounts are also labeled.

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Each of these seamounts is a shield volcano formed as the Pacific Plate moved first northward then northwestward over the Hawai'ian Hotspot, a plume of asthenosphere rising from deep within Earth's mantle.

Geophysical observations such as those used to document these seamounts were crucial in developing and confirming the Theory of Plate Tectonics.