Why do guyots have flat summits?
A guyot is a seamount with a distinctly flattened top. Many are explained as former volcanic islands eroded by waves and later submerged. Not all seamounts have flat summits.
From volcanic island to submerged mountain
An ocean-floor volcano can grow into an island. Waves eroding its upper part near sea level can create a broad, flatter surface. Cooling and subsidence of oceanic crust, or changes in relative sea level, may then carry that surface below effective wave erosion. The old platform can thus survive underwater. Later sedimentation and biological accumulation may further modify its appearance.
Reconstructing the past
A flat summit suggests former proximity to sea level, but rock samples and dating are needed to establish its history. Bathymetric maps reveal height, side slopes and neighbouring structures. A guyot is an isolated oceanic elevation, not a trench or continental shelf. Its interaction with currents can influence local habitats, although identical biological richness should not be assumed for all guyots.