MORPHOLOGY AND DISTRIBUTION OF SEAMOUNTS SURROUNDING EASTER ISLAND

We investigate the morphology and distribution of a seamount populatio n on a section of seafloor influenced by both superfast seafloor sprea ding and hotspot volcanism. The population under investigation is part of a broad chain of seamounts extending eastward from the East Pacifi c Rise, near Easter Island. In order to define the morphological varia bility of the seamounts, basal shape, cross-sectional area, volume, fl atness, and flank slope are plotted against height for 383 seamounts w ith heights greater than 200! m, based on bathymetry data collected by GLORI-B and SeaBeam 2000, during three cruises onboard the R/V Melvil le in the spring of 1993. Nearly complete swath mapping coverage of th e seamounts is available for the analysis of size and shape distributi on. We quantitatively describe the seamount population of this active region, in which seamounts cover similar to 27% of the seafloor, and a ccount for similar to 4.2% of the total crustal volume. Over 50% of th e total volume (61,000 km(3)) of seamounts used in this study is made up by the 14 largest seamounts, and the remaining volume is made up by the 369 smaller seamounts (>200 m in height). Our analysis indicates there are at least two seamount populations in the Easter Island-Salas y Gomez Island (25 degrees-29 degrees S, 113 degrees-104 degrees W) s tudy area. One population of seamounts is composed of short seamounts (<1200 m in height) with variable flatness from pointy cones to flatte ned domes (flatness from 0.01 to 0.57) and predominantly steep flanks (slopes from 5 degrees to 32 degrees). A second population is of massi ve (>1200 m), shield-like, pointy cones (flatness <0.2) and gentle slo pes (from 5 degrees to 15 degrees). An exponential maximum likelihood distribution is fit to the binned raw frequency of height and gives a characteristic height of the seamount population of 308+/-12 m and an expected number of seamounts per 1000 km(2) of 2.7+/-0.15. Many seamou nts that have different slope and flatness relationships with height a re formed next to each other. We speculate that the larger volcanoes ( >similar to 1200 m) originate exclusively from a hotspot source, but o nly a pot-tron of the smaller volcanoes (<similar to 1200 m) are forme d from a hotspot source. The remainder would be presumably formed by a normal mantle or mixed source.