It's not accurate to say that the greatest mountain ranges are under the ocean. While the Mid-Ocean Ridge is the longest mountain range on Earth, stretching for over 40,000 miles, its peaks are submerged. However, the Himalayas, located on land, boast the highest peaks on Earth, including Mount Everest.

Here's why the Mid-Ocean Ridge is underwater:

* Plate Tectonics: The Mid-Ocean Ridge is formed by divergent plate boundaries, where tectonic plates move apart. Magma rises from the Earth's mantle, cools, and solidifies, creating new oceanic crust. This process leads to the formation of a continuous underwater mountain range.

* Seafloor Spreading: The new crust formed at the Mid-Ocean Ridge pushes older crust away, causing the seafloor to spread. This process is responsible for the ocean's vastness.

* Submergence: The Mid-Ocean Ridge is situated on the ocean floor, making it naturally submerged. Its peaks are generally lower than those of the Himalayas, which are formed by the collision of continental plates.

Therefore, the reason the Mid-Ocean Ridge is underwater is due to its formation process and location at the bottom of the ocean. While it's the longest mountain range, the Himalayas still hold the title of having the highest peaks.