Mauna Kea is taller than Everest from base to summit
Measured from its base on the ocean floor, Mauna Kea rises more than 10,000 meters, taller than Mount Everest's height above sea level.

Why it is true
The comparison uses two different reference points. Everest remains the highest point above mean sea level, while most of Mauna Kea is hidden beneath the Pacific Ocean.
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Open NOAA Ocean Service