Mauna Kea is a part of 5 volcanoes that form the Island of Hawai'i.
Mauna Kea began as a preshield volcano driven by the Hawai'ian hotspot about a million years ago, and in it's shield stage it erupted very actively until 500,000 years ago. Right now it is in it's post shield stage, and it is currently dormant. However, it may erupt again and it is under considerable study. The lava that builds this volcano are tholeiitic basalts, consisting of magma and subducted oceanic crust mixed together.
Mauna Kea is located in the Pacific Ocean on the northeast side of the Island of Hawai'i. It is very large compared to the other volcanoes on the island, but smaller than the massive Mauna Loa.