Lonely Planet review
This is the easiest way to summit 'Long Mountain' because you drive up to 11,150ft on the 19-mile Mauna Loa Observatory Rd and then pick up the 6.4-mile trail for the remaining 2527ft to the top. Still, it's a steep, all-day adventure, but one that allows the average hiker to conquer a 13,000ft mountain; it also means you can summit Mauna Loa one day and Mauna Kea the next for a double peak extravaganza.
The drive-hike combination means you have to acclimatize properly, but even that is no guarantee against altitude sickness. The faster and/or higher you go increases your risk. The only remedy is to descend. Sleeping in your car near the observatory or camping along one of the 4WD roads en route might help. You only need a permit from the Kilauea Visitor Center if you want to stay overnight at Mauna Loa cabin .
Begin early. You don't want to be on the mountain when the customary afternoon clouds roll in. Heavy fog is a real danger here, since it obscures the cairns marking the trail. If fog rolls in, find shelter and wait it out, even if this means spending the night. The trail crisscrosses a series of ʻaʻa (rough, jagged lava) and pahoehoe (smooth-flowing lava), most dating from 1942. After about 4 miles and 2000ft in elevation gain, there's a pit toilet and then the trail connects to the Mauna Loa Summit Trail . From the trail junction, it's just over 2.5 miles around the caldera's western side to Mauna Loa summit (13,677ft), or about 2 miles along the caldera's eastern side to Mauna Loa cabin (13,250ft). Perched on the awesome Mokuʻaweoweo Caldera , the cabin offers respite, but if you're on a day trip, push straight on to the summit. It will take half as long to descend. All told, plan on a 10-hour day.