Geologic Map of the Southern Flank of Mauna Loa Volcano, Island of Hawai‘i, Hawaii

Scientific Investigations Map 2932-C
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On the Island of Hawaiʻi, Mauna Loa, the largest volcano on Earth, has erupted 33 times since written descriptions became available in 1832. Some eruptions began with only brief seismic unrest, whereas others followed several months to a year of increased seismicity. Once underway, its eruptions can produce lava flows that may reach the sea in less than 24 hours, severing roads and utilities. In terms of eruption frequency, pre-eruption warning, and rapid flow emplacement, Mauna Loa has great volcanic-hazard potential for the Island of Hawai‘i. Volcanic hazards on Mauna Loa may be anticipated, and risk substantially mitigated, by documenting the past activity to refine our knowledge of the hazards and by alerting the public and local government officials of our findings and their implications for hazards assessments and risk.

Although most Mauna Loa eruptions begin in the summit area at 12,000 feet (ft) elevation, the Southwest Rift Zone (SWRZ) was the source of at least 10 flank eruptions since 1843. The SWRZ extends from the summit towards Kalae (South Point) at sea level. The lowermost part of this rift zone, marked by Pu‘uʻoke‘oke‘o to the north at 6,874 ft elevation and extending to the sea, makes up the lower SWRZ. The community of Hawaiian Ocean View Estates, with a population of about 2,500, is the largest in the region. The subdivision is built entirely on flows erupted from southern Mauna Loa, and some source vents are located within the subdivision. Approximately 25 percent of the subdivision is within Hazard Zone 1.

From east to west, the map covers the area from Punalu‘u to Miloli‘i and, from north to south, extends from north of Pu‘uʻoke‘oke‘o to Kalae (South Point). The map encompasses 1,163 square kilometers of the southwest flank of Mauna Loa, from 7,325 ft elevation to sea level. It shows the distribution of eruptive units (flows), which are separated into 16 age groups, ranging from more than 100,000 years before present to A.D. 1950.

Lava erupted from the SWRZ typically flows to the west, east, or south (depending upon vent location relative to the rift crest) and generally produces narrow flow lobes. Both morphologic lava flow types—‘a‘ā and pāhoehoe—are present. In general, the northern part of the mapped area is dominated by flows from the middle SWRZ, whereas the southern part contains flows from the lower SWRZ and includes areas adjacent to, and downslope of, the rift zone. The exceptions are flows that originated from the upper SWRZ in the northeastern part of the Punaluu quadrangle.

Suggested Citation

Trusdell, F.A., and Lockwood, J.P., 2020, Geologic map of the southern flank of Mauna Loa Volcano, Island of Hawai‘i, Hawaii: U.S. Geological Survey Scientific Investigations Map 2932–C, pamphlet 28 p., 2 sheets, scale 1:50,000,

ISSN: 2329-132X (online)

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Geologic map of the southern flank of Mauna Loa Volcano, Island of Hawai‘i, Hawaii
Series title Scientific Investigations Map
Series number 2932
Chapter C
DOI 10.3133/sim2932C
Year Published 2020
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Volcano Science Center
Description Pamphlet: iv, 28 p.; 2 Sheets: 51.88 x 39.18 inches and 38.20 x 38.05 inches; Read Me; Metadata; Database; 1 Appendix
Country United States
State Hawaii
Other Geospatial Southern flank of Mauna Loa Volcano
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details