Overview and Background

Mauna Kea is a dormant volcano on the island of Hawaii. Standing 4,207 m (13,802 ft) above sea level, its peak is the highest point in the state of Hawaii. Much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over 10,000 m (33,000 ft) tall, making it the world's tallest mountain from base to summit, surpassing Mount Everest.

https://en.wikipedia.org/wiki/Mauna_Kea

Lesson Plan and Activity

Mauna Kea: Tallest Mountain

Mauna Kea has an altitude of 4,205 meters (13,796 feet) - much lower than Mount Everest. However, Mauna Kea is an island, and if the distance from the bottom of the nearby Pacific Ocean floor to the peak of the island is measured, then Mauna Kea is "taller" than Mount Everest.

Mauna Kea is over 10,000 meters tall compared to 8,850 meters for Mount Everest - making it the "world's tallest mountain."

http://geology.com/records/highest-mountain-in-the-world.shtml