Most people think of mountain height based on how far their peaks reach into the sky from sea level. This common understanding shapes our perception of the world’s tallest summits. However, a mountain’s true stature can extend far beyond the visible land, stretching deep beneath the ocean’s surface. Investigating these submerged giants reveals a different perspective on what constitutes the tallest mountain on Earth.
The Tallest Ocean Mountain Revealed
When measured from its true geological base to its summit, Mauna Kea stands as the tallest mountain in the ocean. This dormant shield volcano is located on the island of Hawaiʻi in the United States. Its peak rises approximately 4,205 meters (13,796 feet) above sea level, making it the highest point in Hawaii. However, a substantial portion of Mauna Kea lies hidden beneath the Pacific Ocean, extending about 6,000 meters (19,700 feet) to the seafloor. Measured from this deep underwater base to its highest point, Mauna Kea boasts a total height of over 10,205 meters (33,480 feet).
Measuring Mountains From Base to Peak
The traditional method of measuring mountains from sea level provides a limited view of their overall size. Geologists and oceanographers calculate a mountain’s height from its base to its peak. This method accounts for the entire structure, regardless of whether its base begins on land or deep underwater. For mountains originating on the ocean floor, this measurement includes the vast submerged portion that supports the visible peak.
This base-to-peak measurement offers a more complete understanding of a mountain’s geological scale and mass. Like an iceberg, only a small fraction is visible above the waterline, while the majority remains hidden below. Similarly, many ocean mountains are colossal structures with only their uppermost sections breaking the surface. This comprehensive measurement reveals true vertical extent, providing a different perspective on which mountains are truly the largest on our planet.
Mauna Kea Versus Mount Everest
The distinction in measurement methods becomes clear when comparing Mauna Kea to Mount Everest. Mount Everest, located in the Himalayas on the border between Nepal and China, is widely recognized as the highest mountain above sea level, with its summit reaching an elevation of 8,848.86 meters (29,031.7 feet).
In contrast, Mauna Kea’s summit is lower above sea level, at approximately 4,205 meters (13,796 feet). However, its enormous underwater foundation makes it taller overall. Measured from its base on the ocean floor, Mauna Kea’s total height of over 10,205 meters (33,480 feet) surpasses Mount Everest’s height by more than a mile. This comparison highlights that while Everest is the “highest” in terms of elevation above sea level, Mauna Kea is the “tallest” from its foundational base.
How Underwater Mountains Form
Underwater mountains, also known as seamounts, are primarily formed through volcanic activity. Many seamounts are remnants of extinct volcanoes that built up piles of lava on the seafloor. These geological formations often link to the dynamic movements of Earth’s tectonic plates.
One common formation mechanism involves “hotspots,” areas within the Earth’s mantle where plumes of hot rock rise. As a tectonic plate moves over a stationary hotspot, molten rock erupts, creating a series of volcanoes. This process formed the Hawaiian island chain, including Mauna Kea. Seamounts also form along mid-ocean ridges, where tectonic plates spread apart, allowing magma to rise and solidify. Additionally, some seamounts develop at subduction zones, where one oceanic plate slides beneath another, leading to volcanic eruptions as the descending plate melts.