Seamounts are underwater mountains that rise from the seafloor but do not break the ocean’s surface. They are formed from extinct volcanoes and possess steep sides, often with conical shapes. They must rise at least 1,000 meters (3,300 feet) above the surrounding seabed to be classified as a seamount. Found in every ocean basin, estimates suggest over 100,000 exist, though only a small fraction have been explored.
How Seamounts Form
Seamounts primarily form through volcanic activity, where molten rock, or magma, rises from Earth’s mantle and erupts onto the seafloor. This accumulation of lava builds up over time, creating the distinct mountain structures. Many seamounts originate at mid-ocean ridges, which are underwater mountain ranges where tectonic plates are pulling apart, allowing magma to emerge and solidify.
Another common formation mechanism involves mantle hotspots, stationary plumes of hot material rising from deep within the Earth. As an overlying tectonic plate moves across a hotspot, a chain of volcanoes forms, with older, extinct volcanoes moving away from the active hotspot. The Hawaiian Emperor Seamount Chain is a notable example, extending thousands of kilometers from the active Hawaiian Islands. Seamounts can also develop in subduction zones, where one oceanic plate slides beneath another, leading to volcanic activity as magma is generated from the melting of the downgoing plate.
Classifying Seamount Structures
Seamounts are classified by their morphology, exhibiting various shapes and sizes. The most common is the conical seamount, characterized by steep, sloped sides and a pointed or rounded summit, reflecting volcanic origins. They may feature craters at their peaks from past eruptions.
Guyots, or tablemounts, are another type. These flat-topped seamounts were once active volcanoes that may have reached the ocean surface, where wave action eroded their summits flat. Over millions of years, as oceanic crust cools and subsides, these structures sink below sea level. Smaller underwater elevations not meeting the 1,000-meter height criterion are called knolls or pinnacles.
Life on Seamounts
Seamounts are recognized as significant marine habitats, often described as “oases of life” in the deep ocean. Their elevated topography interacts with ocean currents, causing water to rise from deeper layers in a process called upwelling. This upwelling brings nutrient-rich water towards the surface, stimulating the growth of phytoplankton, which forms the base of the marine food web.
The hard, rocky surfaces of seamounts, swept clean of sediment by currents, provide stable attachment points for sessile organisms. Deep-sea corals and sponges, including cold-water corals, thrive in these environments, forming complex, three-dimensional structures. These structures create diverse microhabitats that support a wide array of other marine life, including invertebrates like shrimps, crabs, worms, and brittlestars. Seamounts also serve as gathering points and spawning grounds for many fish species, some commercially valuable, such as tuna and orange roughy. Many seamount species are endemic, meaning they are found nowhere else, highlighting the unique ecological conditions these underwater mountains provide.
Uncovering Seamount Secrets
Exploring seamounts relies on advanced technological tools due to their deep, submerged locations. Multibeam sonar mapping from research vessels is a primary method for discovering and charting them, providing detailed topographic images. This helps scientists understand their shape, size, and geological features.
For closer examination, remotely operated vehicles (ROVs) are deployed. These unmanned submersibles are equipped with cameras, lights, and robotic arms, allowing researchers to observe marine life, collect samples, and conduct experiments from the surface. Autonomous underwater vehicles (AUVs) are also used; these pre-programmed robots survey large areas, collecting data with various sensors. Ongoing exploration continues to deepen our understanding of oceanography, marine biology, and Earth’s geological processes, revealing new insights into these unique and largely unexplored deep-sea environments.