(BIVN) – The geologic history of Mauna Loa’s southeast flank, revealed in a new map, is the topic of this week’s Volcano Watch article written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

The recently published “Geologic map of the central-southeast flank of Mauna Loa volcano” is the culmination of years of field work by the U.S. Geological Survey. This updated map supersedes the “Geologic Map of the Island of Hawaiʻi” (1996) and the “Geologic Map of the State of Hawai‘i” for the Mauna Loa region.



The new map encompasses 195 square miles (506 sq km) of the southeast flank of Mauna Loa – an area equivalent to the islands of Kaho‘olawe and Lānaʻi combined! – and ranges from an elevation of 10,350 feet (3155 m) to sea level.



It includes areas adjacent to and downslope of Mauna Loa’s Northeast Rift Zone, as well as regions east and directly downslope of Moku‘āweoweo, the volcano’s summit caldera. From high on Mauna Loa’s east flank, the mapped area extends toward Hawaiʻi Volcanoes National Park and the community of Volcano (population of approximately 2,000 residents) in the northeast. At the southern boundary of the mapped area is Punalu‘u Bay.

Lava flows from the middle and upper reaches of the Northeast Rift Zone dominate the northern part of the map, comprising about 40 percent of the total area. The map’s southern portion contains flows from the upper Southwest Rift Zone that make up about 2 percent of the total area. Lava from the upper reaches of both rift zones generally forms narrow flow lobes.



The remaining 58 percent of the map (center area) consists of lava flows from the summit of Mauna Loa. In contrast to flows from the rift zones, lava flows derived from the summit caldera form voluminous, broad expansive sheets of pāhoehoe that cover large areas. ‘A‘ā flows occur in this area but are inconsequential when compared to the pāhoehoe flows.



Mauna Loa, the largest active volcano on Earth, is known to have erupted 33 times since written descriptions became available in 1832. Some eruptions were preceded by only brief seismic unrest, while others followed several months to a year of increased seismicity.

Most Mauna Loa eruptions begin in its summit area at or above the 12,000-ft (3658-m) elevation. The central-southeast flank has not been the source of any volcanic activity, although two historical eruptions that began along the Northeast Rift Zone sent flows into the mapped region in 1880 and 1984.