the last eruption of mauna kea was about 4,600 years ago (about 2600 bc); because of this inactivity, mauna kea is assigned a united states geological survey hazard listing of 7 for its summit and 8 for its lower flanks, out of the lowest possible hazard rating of 9 (which is given to the extinct volcano kohala). since 8000 bc lava flows have covered 20% of the volcano's summit and virtually none of its flanks.