Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawai
ʻi in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately 18,000 cubic miles (75,000 km3), although its peak is about 120 feet (37 m) lower than that of its neighbor, Mauna Kea
Mauna Loa has probably been erupting for at least 700,000 years, and may have emerged above sea level about 400,000 years ago. The oldest-known dated rocks are not older than 200,000 years.
Mauna Loa's most recent eruption occurred from March 24, 1984, through April 15, 1984. No recent eruptions of the volcano have caused fatalities, but eruptions in 1926 and 1950 destroyed villages, and the city of Hilo
is partly built on lava flows from the late 19th century.
Mauna Loa is the world's largest shield volcano in terms of area covered. Mauna Loa is shaped like a shield, because its lava is extremely fluid (it has low viscosity), and its slopes are not steep. Eruptions are rarely violent, and the most common form is in the Hawaiian style, which involves lava fountains feeding lava flows.
A summit shelter was built with some of the stones from Wilkes' camp site and mortar in 1934. In 1916 Mokuʻāweoweo was included in Hawaii Volcanoes National Park
, and a new trail was built directly from park headquarters at Kīlauea
, an even more direct route than the one taken by Wilkes. This trail, arriving at the summit from the east via Red Hill
, became the preferred route due to its easier access and gentler slope. After falling into disuse, the historic ʻAinapō Trail was reopened in the 1990s. A third modern route to the summit is from the Saddle Road, up to the Mauna Loa Observatory
which is located at the elevation of 11,135 feet (3,394 m) a few miles north of Mokuʻāweoweo, and the North Pit trail.
The location of Mauna Loa has made it an important location for atmospheric monitoring by the Global Atmosphere Watch and other scientific observations. The Mauna Loa Solar Observatory
(MLSO), located at 11,155 feet (3,400 m) on the northern slope of the mountain, has long been prominent in observations of the Sun. The NOAA Mauna Loa Observatory (MLO) is located close by. From its location well above local human-generated influences, the MLO monitors the global atmosphere, including the greenhouse gas carbon dioxide. Measurements are adjusted to account for local outgassing of CO2 from the volcano.
The Hawaiian Volcano Observatory maintains seismic sensors and a web cam on Mokuʻāweoweo.