The Geology of the Manu'a Islands, Samoa

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1968-10

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University of Hawai'i Press

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The Manu'a Islands are a group of three islands-Ta'u, Ofu, and Olosega-that were built by volcanic activity along the crest of the easternmost portion of the Samoan Ridge. Ta'u Island represents the largest volcanic center, where aa and pahoehoe flows of non-porphyritic basalt, olivine basalt, pierite basalt, and feldspar-phyric basalts constructed a volcanic shield more than 3,000 feet above sea level. The present-day total thickness of this volcanic material is over 12,000 feet, as measured from the ocean floor to the summit of Ta'u, Lata Mountain (3,056 feet). Dips of the lava flows frequently exceed 30°, but average 20-25°. Summit collapse formed a caldera that became partially filled with ponded lavas and pyroclastic deposits which accumulated to a thickness of over 1,000 feet. From the summit area, two rift zones radiate to the northeast and northwest, the latter coinciding with the trend of the Samoan Ridge. Two smaller shields are located along these rift zones. Following a period of extensive erosion, the northeast corner of the island was built out by dunite-bearing lava flows, upon which the village of Fitiiuta now stands. A tuff complex containing large dunite xenoliths and coral blocks extended the northwest corner of the island near the village of Faleasao, burying a former sea cliff.

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Stice GD, McCoy FW Jr. 1968. The geology of the Manu'a Islands, Samoa. Pac Sci 22(4): 427-457.

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