Mauna Kea is the highest island mountain in the world. It is actually a dormant volcano.
Millions of years ago, volcanic eruptions on the sea floor started the process of creating a volcanic mountain. This underwater mountain grew taller and taller, till it rose above the surface of the ocean. As the eruptions continued, the mountain continued to grow, until it reached its present height.
Standing 4,207 metre above sea level, its peak is the highest point in the state of Hawaii. It is actually much taller than Mount Everest, but since water much of Mauna Kea is under water, Mount Everest is still considered to be the world’s tallest mountain. Mauna Kea is over a million years old, and has been dormant now for around 6000 years.