The question of the world’s tallest mountain seems settled, but the answer depends entirely on the reference point used for measurement. Earth’s surface is mostly covered by water, concealing vast topography on the ocean floor that challenges our common understanding of planetary peaks. Hidden beneath the waves is a geological giant that redefines what it means to be the tallest mountain on the planet. This submerged landscape holds the secret to a mountain whose true scale dwarfs even the most famous terrestrial summits. Geologists and oceanographers must use specific metrics to reveal the true magnitude of these hidden structures.
Clarifying the Metric: Elevation vs. Total Height
The height of a mountain can be measured in two fundamentally different ways, which determines the ranking of the world’s tallest peaks. The standard measurement, known as elevation, calculates the vertical distance of a mountain’s summit above mean sea level. This is the metric used to crown Mount Everest as the highest point on Earth, with its summit reaching 29,032 feet (8,848 meters) above the surface of the sea.
A second, more comprehensive method measures the total vertical height, also called base-to-peak height. This technique calculates the full distance from the mountain’s base on the surrounding land or seafloor to its highest point. For mountains whose bases are located deep beneath the ocean, this measurement reveals their complete geological scale, including the massive portion below sea level. The question about the tallest mountain “below sea level” is answered by applying this base-to-peak metric to submerged structures.
This distinction is crucial because mountains formed on continental crust, like Everest, have bases that are already high above the true geological base. Oceanic mountains often rise from flat abyssal plains, giving them a much greater measurable vertical extent. Total vertical height allows for an accurate comparison of the mass and size of mountains, regardless of whether their base is terrestrial or submerged.
The World’s Tallest Mountain (Base-to-Peak Measurement)
When measured from its true base on the ocean floor, the Hawaiian volcano Mauna Kea takes the title of the world’s tallest mountain. This massive dormant shield volcano rises from the bottom of the Pacific Ocean. Its base rests on the deep seafloor, approximately 19,700 feet (6,000 meters) below the surface of the water.
From that submerged base, the mountain rises over 33,500 feet (10,210 meters) to its summit. While its peak stands at an elevation of 13,796 feet (4,205 meters) above sea level, the immense volume of the mountain lies hidden beneath the waves. The total vertical height of Mauna Kea surpasses Mount Everest’s elevation by over a mile.
Mauna Kea’s size is a result of its geological origin as a shield volcano, created by continuous, fluid lava flows over a stationary hotspot in the Earth’s mantle. The dense oceanic crust on which it sits is more capable of supporting the massive weight of this structure than the lighter continental crust supporting the Himalayas. This formation process, which built the mountain from the abyssal plain, allows for its extraordinary base-to-peak dimension.
Distinguishing Seamounts and Ocean Trenches
While Mauna Kea has the largest portion below sea level, the phrase “tallest mountain entirely below sea level” points to other distinct underwater features. Seamounts are mountains that rise from the ocean floor but do not break the surface of the water. They are typically extinct volcanoes, defined as features that rise at least 3,281 feet (1,000 meters) above the surrounding seafloor.
Individual seamounts can be quite large, with the tallest examples rising up to 13,000 feet (4,000 meters) from the seabed. However, even the largest fully submerged seamounts do not approach the vertical height of Mauna Kea’s submerged portion alone, which is about 19,700 feet (6,000 meters). These underwater peaks represent the literal interpretation of a mountain below sea level.
In contrast to mountains, ocean trenches are the deepest depressions in the seafloor. The Mariana Trench in the western Pacific Ocean contains the deepest point on Earth, known as the Challenger Deep. This location plunges to a depth of about 35,876 feet (10,935 meters) below sea level.
Ocean trenches are formed where one tectonic plate is forced beneath another, creating a crescent-shaped scar in the crust. This depth is a staggering contrast to the height of mountains, representing the lowest known point on the planet’s surface. While both seamounts and trenches are significant features of the underwater landscape, Mauna Kea holds the title for the largest mountain structure extending below the sea.