ʻĀinapō Trail, Historic hiking trail on Mauna Loa, Hawaii, United States

The ʻĀinapō Trail is a 35-mile (55 km) route that climbs the southeast flank of Mauna Loa from Kapapala, near present-day Pahala, at about 2,000 feet (610 m) to the rim of Mokuʻāweoweo caldera above 13,200 feet (4,000 m). Mid-elevation sections lie under heavy cloud, while higher up the ground is dry, barren lava rock. The surviving historic stretch, about 11 miles (18 km) above 11,650 feet (3,550 m), ends near Mauna Loa Cabin in Hawaiʻi Volcanoes National Park.

The route was first explored in 1794 by an expedition led by Archibald Menzies, who used barometric instruments to measure the mountain's elevation. This early scientific investigation helped establish the summit as an important location for further geographic and meteorological study.

The name ʻāina pō means 'darkened land' in Hawaiian, referencing the thick cloud cover that blankets the middle elevation sections. This name reflects what hikers experience as they move through the misty and moisture-laden portions of the ascent.

The historic section survives only above 11,650 feet (3,550 m), about 11 miles (18 km) of the route; the lower slopes through Kapapala are private ranch land. A modern shelter stands at a historic campsite at 7,750 feet (2,360 m). Modern trails start from a trailhead on Ainapo Road north of Hawaii Belt Road, cross the Kapapala State Forest Reserve and join the historic path to the summit.

A section of roughly 11 miles above 11,650 feet has remained unchanged since prehistoric times, displaying a stark lava landscape that sits above the cloud layer. This high terrain offers a rare view of the mountain's geological and climatic extremes.