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

Scientific Investigations Map 2932-E
By:  and 



Mauna Loa, the largest active volcano on Earth, has erupted 34 times since written descriptions became available in A.D. 1832. The most recent eruption of Mauna Loa occurred on November 27, 2022, after a 38 year hiatus; it lasted for 12 days. Some eruptions began with only brief seismic unrest, whereas others followed several months to a year of increased seismicity. Once underway, Mauna Loa’s eruptions can produce lava flows that may reach the sea in less than 24 hours, severing roads and utilities. For example, lava flows that erupted from the Southwest Rift Zone in 1950 advanced at an average rate of 9.3 kilometers per hour (5.8 miles per hour); all three lobes reached the ocean within ~24 hours. Near the eruptive vents, the flows likely traveled even faster. 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 can be anticipated, and risk substantially mitigated, by documenting its 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.

The map of the north and west flanks of Mauna Loa shows the distribution and relation of volcanic and surficial sedimentary deposits. It incorporates previously reported work published as generalized small-scale maps and a more detailed map.

Within the mapped area, lava has flowed from three different source regions: the Northeast Rift Zone (22 percent), the summit (64 percent), and radial vents (14 percent). All three have different points of origin which, in turn, affect the flow characteristics and periodicity of activity.

The map area includes the uppermost part of the NERZ and extends from the highest elevation––13,040 feet at the south end of the Kokoolau quadrangle, just below the summit caldera––to the sea northwest and west of the summit. Lava that erupts from the north and west flanks typically flows to the west, northwest, or north, depending on the vent location. Both morphologic lava flow types—‘a‘ā and pāhoehoe—are present. Pāhoehoe units tend to spread out or widen in low-slope regions, such as in the saddle regions between Mauna Loa and Mauna Kea or between Mauna Loa and Hualālai. In comparison, ʻaʻā flows generally produce narrower flow lobes that have higher relief.

This map is the fifth in a series of five maps that will cover Mauna Loa volcano.

NOTE: Map sheet 1 contains lines and type with overprint. This feature may be turned on or off in the Adobe Acrobat page display preferences.

Suggested Citation

Trusdell, F.A., and Lockwood, J.P., 2024, Geologic map of the northwest flank of Mauna Loa volcano, Island of Hawai‘i, Hawaii: U.S. Geological Survey Scientific Investigations Map 2932–E, 2 sheets, scale 1:50,000, pamphlet 37 p.,

ISSN: 2329-132X (online)

ISSN: 2329-1311 (print)

Study Area

Table of Contents

  • Mauna Loa
  • Physiography
  • Mapping Project
  • Map of the Northwest Flank of Mauna Loa
  • Mapping Methods
  • Database
  • Acknowledgments
  • Geology
  • Volcanic Deposits
  • Radiocarbon Data
  • Fault Systems
  • Map Unit Labels and Flow Identification Number (FIDFID)
  • Description of Map Units
  • References Cited
  • Appendix 1. Rejected Radiocarbon Ages
  • Appendix 2. Geochemical Analyses of the Major Units for the Geologic Map of the Northwest Flank of Mauna Loa Volcano
Publication type Report
Publication Subtype USGS Numbered Series
Title Geologic map of the northwest flank of Mauna Loa volcano, Island of Hawai‘i, Hawaii
Series title Scientific Investigations Map
Series number 2932
Chapter E
DOI 10.3133/sim2932E
Year Published 2024
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Volcano Science Center
Description Pamphlet: iv, 37 p.; 2 Sheets: 59.43 × 68.58 inches and 50.12 × 52.06 inches; 2 Appendices; Read Me; Metadata; Spatial Data
Country United States
State Hawaii
Other Geospatial Mauna Loa Volcano
Online Only (Y/N) N
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details