A'asu Valley Project

Geography of Samoa and the A’asu Valley

The Samoan archipelago is located between 168º and 173º West Longitude, and 14º35' and 13º20' South Latitude, in the South Pacific. It is considered part of the "Polynesian Triangle" of islands that stretch from Rapa Nui (Easter Island) in the east, to New Zealand in the west, and as far north as the Hawaiian Islands. The nearest major islands to the Samoan archipelago are Tonga, located approximately 750 miles to the south-southwest, and Fiji, approximately 780 miles to the southwest. The Samoan islands are almost completely volcanic in origin. Historically, the intra-island cultures of the Samoan archipelago have many affinities, were close traders, and were sometimes combatants. Since 1900 the Samoan islands have been divided politically between the U.S. territory of American Samoa to the east, and the now independent nation of Samoa to the west.

American Samoa consists of four large volcanic islands and a number of smaller ones. From west to east the larger islands are Tutuila, Ofu, Olosega, and Ta’u, Islands. Further to the east is an atoll, Rose Island. Like the rest of the Samoan archipelago, they are the result of submarine volcanic activity that built up to form mountains that emerged on an east-trending plate, sometime during the late Pliocene (Stearns 1944).

Tutuila is the largest island, and the seat of government. Tutuila itself was formed by the coalescence of five volcanoes on at least two separate submarine rifts. The bulk of the island's mountains are basalt, basaltic tufts, and lava. Other volcanic rocks make up a fraction of the remaining geology, and coral sands contribute strongly to its shoreline. Stearns reports that Tutuila has experienced at least 6.1 m (20’ ft) of emergence relative to the contemporary sea level since the Pleistocene. Some of the principle evidence for this uplift is visible from Massacre Bay at A’asu. Sea caves exist on the western side of the bay, the roof of which is about 15.2 m (50 ft) above modern sea level. A similar cave lies on the west side of Afono Bay, suggesting to Stearns that Tutuila has emerged on the order of 7.6 m (25 ft) since the Pleistocene (Stearns 1944:1309). Coral remnants are also found in some locations within the bay, about 1.5 m (5 ft) above the contemporary sea level (Stearns 1944:1308). This compares well with paleo-indicators of sea level noted by others around the island which also indicate about 1.5 m of sea level change, thought to have occurred during the mid to late Holocene (Nunn 1998).

The A’asu valley is a lush canyon on the northern shores of western Tutuila. It lies approximately 2.5 miles west of Fagasa Bay, and 4 miles northwest of Pago Pago, at 170º45’30” West Longitude by 14º17’51” South Latitude. The valley floor extends about 0.5 km (0.3 mi) inland, comprising about 0.10 km2 (about 25 acres) of relatively flat terrain. A small adjacent valley adds only 0.03 km2 (about 7.5 acres). A considerable stream of fresh water divides the A’asu Valley bottom. A’asu Stream, derives from runoff and two springs high in the mountains. The springs possibly provided a perennial source of fresh water throughout the Holocene that might have made this valley particularly attractive to prehistoric inhabitants. The entire basin drains only about 2.7 km2 (about 1.03 mi2), with an average discharge of about 6.09 cubic ft/sec (Wong 1999:37). Its variability in flow is among the lowest on the island, and even in the driest years of record it discharged more fresh water than any stream monitored by the USGS (Wong 1999). A village at the mouth of the basin was inhabited when the first Europeans made contact with the Tutuilans. Indeed, the moniker of “Massacre Bay” refers to the first untoward action by Samoans towards a European expedition (see below). The valley has been in continuous utilization since that time, but over the past forty years there has been a slow migration out of the valley and into the mountains to the upland settlement of A’asufou (“New A’asu”).