Mauna Kea is a dormant volcano on the island of Hawaii. Its peak is 4,207.3 m (13,803 ft) above sea level, making it the highest point in the state of Hawaii. Most of the volcano is underwater, and when measured from its underwater base, Mauna Kea is the tallest mountain in the world, measuring over 10,000 m (33,000 ft) in height. Mauna Kea is about a million years old, and has thus passed the most active shield stage of life hundreds of thousands of years ago. In its current post-shield state, its lava is more viscous, resulting in a steeper profile. Late volcanism has also given it a much rougher appearance than its neighboring volcanoes due to construction of cinder cones, decentralization of its rift zones, glaciation on its peak, and weathering by the prevailing trade winds. Mauna Kea last erupted 6,000 to 4,000 years ago and is now considered dormant. The peak is about 38 m (125 ft) higher than Mauna Loa, its more massive neighbor.