A shorter route to Mauna Loa's summit is via the Observatory Trail. The Observatory trail ascends 1,975 feet in 3.8 miles from the Mauna Loa Weather Observatory to the rim of Moku'aweoweo Caldera (North Pit). Here the trail splits. Take the trail to the right another 2.6 miles to the true summit. Take the trail to the left another 2.1 miles along the rim to the Mauna Loa cabin. Not as interesting geologically as the Mauna Loa trail, this route does offer good views of Mauna Kea.
It is possible to hike to the summit of Mauna Loa and back in one day via the Observatory Trail Be sure you are well prepared. The trail is rough and remote - few folks come here. If you plan to stay overnight at the Mauna Loa Cabin, you must register with the Park Service before beginning your hike.
Accessible by a one-lane paved road. No public telephones or public transportation. It takes about two hours to drive to the Observatory trailhead via Saddle Road. The Saddle Road (Hwy 200) begins in Hilo, is not in the national park, and although it has been recently paved, most car rental companies still prohibit driving on it.
From downtown Hilo, drive up the Saddle Road 29 miles to Pu`u Huluhulu, turn left, and continue 18 miles to the Mauna Loa Weather Observatory. The road has very little traffic, so the chances for hitchhiking up or down are slim. Park in the parking lot for hikers. To begin the hike to the North Pit, head west along the jeep trail past the parking lot.
There is no drinking water at the Mauna Loa Observatory trailhead so plan accordingly. The trail begins where the MLO road ends. It is like walking on a scree field. Follow this road for about a half mile, where you will pick up the Observatory Trail on your left. The turnoff is well marked with a sign. The trail itself is just a series of cairns (ahu), one after the other. It is recommended that don’t loose sight of the ahu behind you until you find the one ahead of you as it is easy to become disoriented on the broad face of the mountain or in the frequent fog. After a mile or so you will reach a large broken lava tube marked by two large ahu. A lava rock wall has been built around it creating a nice shelter. The trail then continues over mixed ‘a‘hoehoe lava fields.
Continuing up the mountain the trail crosses the same 4-wheel drive road and after a short distance, again meets up with the road but this time the trail makes a sharp left and follows the road until it reaches a locked gate. The trail then cuts to the right off the road and there is a sign that you are entering Hawai’i Volcanoes National Park. For about a half mile the trail is on well defined loose volcanic cinder. There is one more crossing of the road and then you cross a less steep section of smooth hoehoe lava right up to the trail junction of the Mauna Loa, Summit, and Mauna Loa Cabin Trails. There is a well marked good pit toilet a hundred or so yards before this large train junction which precariously straddles a rift in the lava.
Just about 25 feet north of the trail junction with the Summit Trail is a nice recessed sheltered pit which is out of the wind and offers a slight bit of shade after hours in the sun.
|MAUNA LOA WEATHER OBSERVATORY TO NORTH PIT|
|0.0||11055||Sign: "OBSERVATORY TRAIL, CABIN/SUMMIT TRAIL JCT 3.5, MAUNA LOA CABIN 5.6, MAUNA LOA SUMMIT 6.0." Add 0.3 mi to these distances to account for the jeep trail length. Begin in Koko`olau Quadrangle.|
|0.3||11182||Sign: "OBSERVATORY TRAIL, MAUNA LOA CABIN 5.6, MAUNA LOA SUMMIT 6.0." The trail goes up and south from here. Follow ahu and a slightly worn trail on prehistoric lava. This trail was once marked with yellow spots painted on the rocks; you will probably see these spots chipped out of the lava.|
|0.9||11545||The brown `a`a flow at the left is prehistoric.|
|1.2||11684||The trail crosses the jeep trail here. This road was built in 1951 to 13450 feet where the first weather observatory was located. After negotiating this miserable road for a few years, the weather observatory was moved to its present location in 1956.|
|1.3||11768||BM 1978 HVO22.|
|1.5||11805||A spacious lava tube is marked by two large ahu. Turn around and take a last look at the Weather Observatory. The trail continues to the right following the small ahu (ignore the one at the left).|
|1.6||11933||BM 1978 HVO21.|
|1.6||12000||The trail crosses a prehistoric `a`a flow.|
|1.7||12045||To the left (east) is a prehistoric patter cone that lies on the north flank of Mauna Loa.|
|2.2||12377||Sign: "TRAIL." The old trail continued straight from here, but in 1983, it was rerouted to an easier route. Dog-leg to the left. The rusty brown spots in the grey pahoehoe are weathered olivine crystals.|
|2.4||12425||Sign: "TRAIL." The trail continues along the jeep trail to the east-southeast. The olivine crystals in the lava here are plentiful.|
|2.6||12475||Passing another jeep trail to the left.|
|2.7||12500||Sign: "TRAIL." Just ahead of this point is a locked gate across the road. The jeep trail above here is for use only by HVO and Park Service personnel. The trail turns right (south), following a fissure that produced the flow that the Mauna Loa Observatory lies on.|
|3.1||12780||The 1942 shiny black pahoehoe flow lies to the right.|
|3.2||12795||The trail crosses onto the 1942 lava.|
|3.3||12862||Sign: "TRAIL." Cross the jeep trail straight ahead.|
|3.5||12970||Leave Koko`olau Quadrangle and enter Mauna Loa Quad.|
|3.6||12973||The trail crosses the 1942 fissure.|
|3.7||12989||To the right, placed over a crack, is a primitive toilet.|
|3.8||13018||Sign to the left: "CABIN TRAIL, MAUNA LOA TRAIL .1, MAUNA LOA CABIN 2.1." Sign to the right: "SUMMIT TRAIL, MAUNA LOA SUMMIT 2.5." Sign behind pointing back down to the Weather Observatory: "OBSERVATORY TRAIL, MAUNA LOA OBSERVATORY 3.5." (The distance to the Observatory is really 3.8 miles.)|
Overnight backcountry users must register and obtain a free permit at the Kilauea Visitor Center (7:45 a.m. to 4:45 p.m. daily). Permits are issued on a first-come basis no earlier than the day before your hike. Stays are limited to 3 nights per site; group size is limited to 12 people. A total of 16 hikers are allowed per night at the Mauna Loa summit cabin (there are only 12 bunks at the cabin).
Backpackers to Mauna Loa should be adequately equipped, experienced in wilderness/high altitude trekking, and physically fit.