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The Geology of the Manu'a Islands, Samoa

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Title:The Geology of the Manu'a Islands, Samoa
Authors:Stice, Gary D.
McCoy, Floyd W Jr.
Date Issued:Oct 1968
Publisher:University of Hawai'i Press
Citation:Stice GD, McCoy FW Jr. 1968. The geology of the Manu'a Islands, Samoa. Pac Sci 22(4): 427-457.
Abstract: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.
Appears in Collections: Pacific Science Volume 22, Number 4, 1968

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