For several reasons:
- Rugged, Young Mountains
The island of New Guinea lies in an active margin setting, and a chain of rugged, young mountains,
many more than 2000 m (6562 ft) in elevation, extend along the axis of the island. The Fly River
drains this region.
- High Rainfall Rates
Over the mountains of New Guinea annual rainfall rates are more than 10 m/year (33 ft/year).
As a comparison, New York City receives approximately 47 inches annually or 3.9 ft/year (1.2 m/year).
- Large Sediment Supply Signal to Ocean
Factors listed in #1 and #2 along with the humid climate and
earthquake activity are responsible for a tremendous discharge of sediment
and dissolved material from New Guinea to the coastal ocean. In total,
it is estimated that the island contributes 1.7 billion metric tonnes
(3.7 trillion lbs.) of sediment to the ocean annually, approximately 1.5
times the sediment discharge of the Amazon River (Milliman). Furthermore,
New Guinea and five islands of the Indo-Pacific region are estimated to
contribute 20-25% of the total sediment discharge to the ocean, emphasizing
the critical importance of the area to the ocean.
- Wide Continental Shelf
The Fly River discharges its large sediment load onto a relatively wide continental shelf. Therefore,
the primary marine depocenter (i.e., the location where most sediments deposit) is immediately seaward
of the river mouth, and this is likely an excellent record of past sediment discharge.
- An Undisturbed System
Unlike most large rivers around the world, the Fly River drainage basin has been relatively undisturbed by humans.
Two mines are found along the river system, but otherwise, urban development is essentially absent in the 75,000
- Existing Data
Because Ok Tedi mine is located on the Fly River system, the river has been well studied and a considerable amount
of data (e.g., river gauge measurements) exists for this relatively remote river. Also, a significant amount of
preliminary sedimentological and geochemical research has been conducted on the shelf seaward of the mouth of the
Fly River. Consequently, the basic mechanics of sediment dispersal and accumulation throughout the system are believed
to be understood.