american samoa - University of Hawaii at Manoa

I. INTRODUCTION
The Geography
Samoa is a volcanic archipelago situated in the
south I'acitic Ocean at a latitude of 13 - 15" south
and a longitude of 168 - 173" west, and runs in a
west-northwest direction east of Fiji, north of Tonga,
south of Tokelau, and west of Niue and the Cook
Islands (Fig. 1). It comprises nine inhabited
volcanic islands and two distant atolls, and has a
total area of ca. 3 100 km2. The archipelago is
divided politically into Western Samoa, which is an
independent country, and American Samoa, which is
an unincorporated territory of the United States.
American Samoa, which comprises the east end
of the archipelago, consists of five main volcanic
islands (Tutuila, 'Aunu'u, Ofu, Olosega, and Ta'u)
and two atolls (Rose and Swains). Tutuila, on which
this unit of the new proposed park is located (other
units are on Ofu and Ta'u), is the westernmost and
by far the largest of the islands of American Samoa.
It has an area of approximately 142 km2 and a
maximum elevation of 653 m on top of Matafao
(Amerson et a/. 1982).
The proposed Tutuila unit of the National Park of
American Samoa is located on the north central part
of the island, between the villages of Fagasa on the
west and Afono on the east (Fig. 2 & 3). The village
of Vatia is situated in the center of the park, and the
boundaries around it begin at about the 200 ft
elevational line. The northern boundary is the
I'acific Ocean, and the southern boundary is the
slope leading from Pago Pago Harbor up to Alava
Ridge. The highest elevation in the Tutuila unit of
the park is Mt. Alava at 490 m (1610 ft), where a
TV tower is located, and the total area of the park is
2,770 acres (National Park Service 1988). The Ofu
unit is discussed in Appendix D.
The CIimate
Since American Samoa comprises small islands
situated between the Tropic of Capricorn and the
Equator, its climate is maritime and tropical. It
belongs to Koeppen's "tropical climate zone"
characterized by average monthly temperatures of
more than 1 8"C, no winter season, and abundant
annual rainfall that exceeds annual evaporation. The
mean daily temperature for Tutuila is 26.7"C (80°F),
with an average maximum daily of 29.7"C (85.4"F)
and an average minimum daily of 23.6"C (74.6"F).
There is not much seasonal variation, with the
warmest month being March (27.2"C, 80.9OF) and
the coolest being August (25.9"C, 78.7"F)
(Nakamura 1984).
The rainfall at the airport at Tafuna on the
south-central coast of Tutuila averages about 3200
mm (124 in) per year (Nakamura 1984). The
monthly average there from October to May is 300
mm (12 in), while in the dry season from June to
September it is 180 mm (7 in). This variation is
strongly affected by the tradewinds, which blow
regularly from the southeast from about April to
December. The months when they are absent are
characterized by storms coming in from other
directions.
Topographic features strongly effect these totals
in some places. For example, Pago Pago, which lies
just to the west of "Rainmaker" (Matafao) mountain,
averages nearly 5000 mm (200 in) a year. There is
probably not too much of a rainshadow effect, since
the island is not very high in elevation, but more
rain would be expected to fall on the south and east
coasts than on the north and west coasts, as in
Western Samoa (Wright 1963).
The relative humidity is constantly high, ranging
between 82 and 86% (at 5 p.m.) throughout the year
(Amerson et al. 1982). Droughts of varying duration
occasionally occur, but these do not have much
permanent effect on the vegetation. Hurricanes, the
most recent of which were in 1987 (known as Tusi),
1990 (Ofa), and 1991 (Val), periodically hit the
islands, but the occurrence of three strong hurricanes
in such close proximity is unusual.
The Geology
Samoa is a volcanic archipelago that is "oceanic"
in origin, i.e., it was formed from basalt rising from
a "hot spot" on the ocean floor of the Pacific plate
beyond the continental islands to the west. The
archipelago was born in isolation, and has never had
a connection to any other land area. The islands
originated in the Pliocene Epoch (over two million
years ago), and were formed generally in a westerly
direction, with the youngest on the west end of the
chain (Savai'i in Western Samoa) and the oldest on
the east end (Rose Atoll). The most recent volcanic
activity in American Samoa was a submarine
eruption between Ta'u and Olosega in 1866. The
only signs of geologically recent volcanism on
Tutuila are the Tafuna Plain, and several adjacent