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Mountains in the Sea

One of the mysteries of the sea are the large number of seamounts that rise up on the seabed and, in a few cases, break surface to form oceanic islands. Volcanic in origin, seamounts are widely scattered throughout the world’s ocean basins, especially in the Pacific. Recent estimates suggest that there maybe as many as 200,000 seamounts with heights above the surrounding seafloor that are in the range 0.1 to 6.7 km. Seamounts are generally circular in shape, have pointed, star-shaped, curved, or flat tops, and are often capped by a coral reef. They are of geological interest because they record the horizontal and vertical motions of the Earth’s tectonic plates, the strength of its hard outermost rock layer, and the magmatic ‘pulse’ of its deep interior. They are also significant as ocean ‘stirring rods’, biodiversity ‘hotspots’, and hazards for earthquakes, landslides, and submarine navigation. 

Unfortunately, there are only a few (<300) sample ages from seamounts and so we do not know how many are like Loihi in the Hawaiian Island chain, which is building up on the seafloor and will eventually form an island or Horizon Guyot in the Mid-Pacific Mountain chain, which was once an island and is now sinking. One problem is sparse ship track coverage that has made seamounts difficult to find. Statistical studies suggest that there maybe as many as 24,000 seamounts higher than 1 km still to be discovered. The charting of these seamounts and the determination of their morphology, structure, and evolution is one of the many challenges facing marine geoscientists in the future. 

Listen to 'Spider Webs and Seamounts' in our series of podcasts to hear Tony Watts explain more about his research into seamounts and their origin.


Tony Watts (University of Oxford)


Tony Watts is Professor of Marine Geology and Geophysics in the Department of Earth Sciences at the University of Oxford. He received his BSc. in Geology and Physics from University College, London and his Ph.D in Marine Geophysics from the University of Durham. After graduating, he joined the Bedford Institute of Oceanography, Dartmouth, Canada and then the Lamont-Doherty Geological Observatory of Columbia University, New York, USA. 

He has participated in some 18 cruises of scientific research ships to each of the world’s ocean basins and has been involved in all aspects of the acquisition, reduction, and interpretation of marine geological and geophysical data. His current research is focussed on the structure and evolution of the Brazilian continental margin, the Canary and Cape Verde Islands, and the Tonga-Kermedec deep-sea trench island arc system.