Beneath the Pacific waves lie massive, flat-topped volcanic mountains known as guyots.

Nature · Published 3 October 2026 Swipe more like this →

In short: Far below the ocean surface, isolated volcanic peaks with strangely flat summits rise from the deep-sea floor. These submerged giants, called guyots, were once islands that breached the surface before sinking into the abyss. Their existence provides a vital record of how tectonic plates drift across the Earth's mantle.

A guyot is defined as an isolated submarine volcanic mountain featuring a flat summit located more than 200 metres below sea level. These structures, also known as tablemounts, can have diameters exceeding 10 kilometres. While they are most abundant in the Pacific Ocean, they have been identified in every ocean except the Arctic. Their sides typically rise gently from the seafloor before steepening to an angle of about 20 degrees near their summits.

The origin of these features is linked to volcanic activity at mid-oceanic ridges. Initially, these mountains form as volcanic islands. During their time at the surface, wave erosion truncates the peaks, creating their characteristic flat tops. Some guyots in the western Pacific are capped by drowned coral reefs that date back to the Late Cretaceous period, between 100 million and 65.5 million years ago. These fossils, along with rounded volcanic boulders, confirm that these mountains were once at shallow depths.

As the seafloor spreads, it moves laterally away from ridge crests and gradually cools, causing the lithosphere to become denser and sink through isostasy. This subsidence carries the former islands deeper into the ocean. While coral growth can sometimes keep pace with this sinking, eventually the reefs dip too deep to survive. Scientists debate why some Cretaceous reefs died; theories include the northward drift of the Pacific Plate into cooler waters or sudden, oxygen-depleted conditions caused by intense seafloor volcanism.

The study of guyots has been instrumental in understanding plate tectonics. By tracing the chains of these seamounts, geologists can map the direction of lithospheric plate movement over fixed heat sources in the asthenosphere. The name itself honours Arnold Henry Guyot, a Swiss American geologist. While the term is also used in viticulture for a specific vine-training method developed by Dr. Jules Guyot, in geology, it represents a permanent, submerged monument to the shifting nature of the Earth's crust.

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