Science for All | What are seamounts?

The Hindu’s weekly Science for All newsletter explains all things Science, without the jargon.

Updated - April 27, 2023 05:59 pm IST

Published - April 26, 2023 04:26 pm IST

Seamounts are either active or dormant volcanoes that rise dramatically from the bottom of the ocean and never reach the surface.

Seamounts are either active or dormant volcanoes that rise dramatically from the bottom of the ocean and never reach the surface.

(This article forms a part of the Science for All newsletter that takes the jargon out of science and puts the fun in! Subscribe now!)

In an astonishing discovery, scientists have reported finding 19,325 new seamounts after poring through new high-resolution data. A 2011 census had already mapped 24,000 seamounts across the world’s oceans. In this week’s edition of Science For All, let’s scale these underwater marvels.

A seamount is an underwater mountain. They are formed through volcanic activity and scientists recognise them as hotspots for marine life. Like volcanoes on land, seamounts can be active, extinct or dormant volcanoes.

Most seamounts are formed near mid-ocean ridges, where the earth’s tectonic plates are moving apart, allowing molten rock to rise to the seafloor. The planet’s two most-studied mid-ocean ridges are the Mid-Atlantic Ridge and the East Pacific Rise.

Some seamounts have also been found near intraplate hotspots – regions of heavy volcanic activity within a plate – and oceanic island chains with volcanic and seismic activity called island arcs.

Because seamounts are formed when molten rock comes up from below the tectonic plates, they provide information about the mantle’s composition and about how tectonic plates evolve.

Oceanographers also study seamounts to understand their influence on how water circulates and absorbs heat and carbon dioxide.

Seamounts are home to diverse biological communities. They are good places for life because they can cause localised ocean upwelling – the process by which nutrient-rich water from deep within the ocean moves up to the surface.

Surveyors map seamounts using one of two modes – echo sounders or multibeam sonar on ships for topographic mapping or using satellite altimetry for gravity-field mapping. Research vessels with multibeam sonar mapping produce hi-res maps but these maps are often incomplete: the places where the vessels don’t go become blindspots. In satellite altimetry, a satellite uses radar to gauge the shape of the seafloor by measuring the time taken for each pulse to bounce off the ground and return. The resulting maps are low-res but have much better coverage.

Since the 2011 seamount survey, altimetry has improved in two key ways. First: European Space Agency launched the CryoSat-2 and Envisat, and NASA and French space agency jointly launched the Jason-1 geodetic missions. They were notable because they helped achieve improved spatial coverage.

In the recent study, scientists from Scripps Institution of Oceanography, U.S.; Chungnam National University, South Korea; and University of Hawaii at Manoa, U.S. reported discovering the new 19,000+ seamounts in data collected by advancements in altimetry for gravity-field mapping.

SARAL, a satellite that India and France developed together for oceanographic studies, made a significant contribution by further reducing radar noise and enabling the expansion of the seamount catalogue.

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