Mauna Kea is the tallest peak in the Hawaiian Islands when measured from its ocean-floor base.
Mauna Kea rises 4,207 metres above sea level, but its volcanic structure extends roughly 6,000 metres below the Pacific Ocean. From its submarine base to its summit, it stands about 10,000 metres tall, making it taller than Mount Everest by that measurement.
The volcano is dormant, with its last known eruption occurring roughly 4,500 years ago. Its summit is exceptionally valuable for astronomy because of its high elevation, dry atmosphere, and limited light pollution. Several major observatories operate there.
Mauna Kea is often confused with Mauna Loa, which is larger by volume and area. Mauna Loa is the world’s largest active shield volcano above sea level, while Mauna Kea is taller from base to summit.