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PACIFIC SCIENCE, Yol. XXII, October 1968 
the largest island in Eastern Samoa, lies about 
60 miles west of the three small Manu’a Islands 
(14-15°S, 169°W), and Rose Atoll, the east- 
ernmost island of Samoa, which is approximately 
100 miles east of the Manu’a Islands. 
The islands of Samoa are located along the 
crest of a submarine ridge which extends over 
300 miles from Savai’i to Rose Atoll and trends 
approximately S 75° E. Apparently this ridge, 
hereafter called the Samoan Ridge, is the topo- 
graphic expression of a regional rift along 
which the various volcanoes in the archipelago 
have erupted. That portion of the ridge between 
Tutuila and the Manu’a Islands is offset to the 
north but has nearly the same trend, S 70° E, 
as the western portion. It seems most likely that 
the ridge at one time was continuous, but it has 
been offset by later left lateral displacements. If 
the Tonga Trench were extended only 100 miles 
north, it would intersect the Samoan Ridge near 
the offset. 
Tutuila is separated by normal oceanic depths 
of greater than 10,000 feet from Upolu to the 
west and the Manu’a Islands to the east. Thus, 
three major volcanic piles are aligned along the 
Samoan Ridge: (1) Savai’i (700 mi 2 above sea 
level) and Upolu (430 mi 2 above sea level), 
which may have been two piles that gradually 
merged; (2) Tutuila (53 mi 2 above sea level) ; 
and (3) Manu’a Islands (19 mi 2 above sea 
level). 
In addition, Rose Atoll (less than 1 mi 2 
above sea level) is the only remaining surface 
expression of a fourth volcanic pile atop the 
Samoan Ridge. In a very general way then, 
volcanic activity moved from east to west, 
whereas in the Hawaiian Islands and the Society 
Islands (Williams, 1933) the volcanic activity 
was from west to east. There have been his- 
toric eruptions on Savai’i and Upolu (Kear and 
Wood, 1959), as well as an historic eruption in 
the Manu’a Islands (Friedlander, 1910). 
Friedlander (1910), the first geologist to 
visit the Manu’a Islands, thought that Ofu and 
Olosega were remnants of a single volcano and 
that the embayments to the north and south rep- 
resented two central craters of collapse that 
nearly coalesced. He pointed out that the lavas 
of Ta’u were relatively recent in age and that 
the scarp on the south side of the island was 
formed by a caldera collapse. He also thought 
that the present sea cliff on the southern shore- 
line of the island was the vestige of further 
collapse. Friedlander was given an eye-witness 
account of a submarine eruption that occurred 
around 1866 between Olosega and Ta’u. 
Daly (1924) spent a few days on a reconnais- j 
sance of the Manu’a Islands, during the course 
of his more complete study of Tutuila, and 
made the following observations: 
(1) The western slope of Ofu and the east- 
ern slope of Olosega largely preserve the con- 
structional profiles of a volcanic cone. 
(2) Cliffs of approximately 300 feet have 
been cut into the islands by the sea, whereas 
