Mauna Kea (mou´nə kā´ə), dormant volcano, 13,796 ft (4,205 m) high, in the south central part of the island of Hawaii. It is the loftiest peak in the Hawaiian Islands and the highest island mountain in the world, rising c.32,000 ft (9,750 m) from the Pacific Ocean floor. It has many cinder cones on its flanks and a great crater at the summit. Its fertile lower slopes are used for agriculture, especially the growing of coffee beans; the upper slopes are snow-covered in winter. At the peak of Mauna Kea, where the dry air is ideal for optical and infrared astronomical observations, is the site of the Mauna Kea Observatories. The mountain is surrounded by the Mauna Kea Forest Reserve; the Mauna Kea Ice Age Natural Area Reserve is on the southern slopes.