Morphology and distribution of seamounts surrounding Easter Island

Abstract

We investigate the morphology and distribution of a seamount population on a section of seafloor influenced by both superfast seafloor spreading and hotspot volcanism. The population under investigation is part of a broad chain of seamounts extending eastward from the East Pacific Rise, near Easter Island. In order to define the morphological variability of the seamounts, basal shape, cross-sectional area, volume, flatness, and flank slope are plotted against height for 383 seamounts with heights greater than 200 m, based on bathymetry data collected by GLORI-B and SeaBeam 2000, during three cruises onboard the R/V Melville in the spring of 1993. Nearly complete swath mapping coverage of the seamounts is available for the analysis of size and shape distribution. We quantitatively describe the seamount population of this active region, in which seamounts cover ∼27% of the seafloor, and account for ∼4.2% of the total crustal volume. Over 50% of the total volume (61,000 km3) 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°-29°S, 113°-104°W) study area. One population of seamounts is composed of short seamounts (<1200 m in height) with variable flatness from pointy cones to flattened domes (flatness from 0.01 to 0.57) and predominantly steep flanks (slopes from 5° to 32°). A second population is of massive (>1200 m), shield-like, pointy cones (flatness < 0.2) and gentle slopes (from 5° to 15°). 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±12m and an expected number of seamounts per 1000 km2 of 2.7±0.15. Many seamounts that have different slope and flatness relationships with height are formed next to each other. We speculate that the larger volcanoes (>∼1200 m) originate exclusively from a hotspot source, but only a portion of the smaller volcanoes (