Mauna Kea on Hawaii s Big Island is a 10000m high volcano, from base to summit, including 6000 metres under the sea making it a taller mountain than Everest-its just that its summit is not at such a high altitude ( 4205m,131796 feet).It is famous for its astronomical observatories which sit like giant golf balls on the top of the snow capped volcano.
The Geology Bit
Mauna Kea is now dormant and only burst into life 400,000 years ago. its last eruption was around 2460 BC. It is thought to have moved away from the Hawaiin hot spot and activity has passed on to its neighbours Mauna Loa and Kilauea.
What to see and How to see it?
At mile 28 off the Kona/Hilo saddle road a road come track, suitable for 4WD only, heads up to the summit of Mauna Kea. The Ellison Onizuka Visitor centre at 2835m may be accessible by normal 2WD but beyond this it is strictly 4WD only. At the visitor centre you can ask about observatory tours.From the Visitor centre it is possible to complete an 14 km( 8 mile) hike to the summit around trip of 8 hours. The summit area does not provided any facilities for hikers and is dedicated to the observatories, so take all your own provisions. There is a short trail to Lake Waiau a blue lake in a crater.
Alternatively trips to the summit can be booked with local companies which gets round the car problem.USGS:Mauna Kea
MaunaKea.com: trips to the summit of mauna Kea
Adventurein hawaii.com : Big Island:Mauna Kea summit
Online Aerial tour of Mauna Kea summit area
Global Volcanism project