The Marine Geomorphology of American Samoa:
Shapes and Distributions of Deep Sea Volcanics

Master of Science, Geography, Oregon State University, Fall 2007
Emphases in Geographic Information Science and Physical Geography

Graduate committee: D. Wright, A. Koppers, R. Keller, G. Klinkhammer

Jed Roberts
Dept of Geosciences, Oregon State Univ
Corvallis, OR 97331-5506
jed.roberts-at-dogami.state.or.us

Abstract.
The geologic processes at work in American Samoa have long been a point
of scientific debate. Of its numerous volcanic formations, few breach sea
level, leaving an enormous proportion of their mass unavailable to
traditional observation. This study aims to describe the deep sea
geomorphology of American Samoa through compilation, quantitative analysis,
and qualitative interpretation of multibeam bathymetry datasets in an effort
to contribute a new perspective on volcanic origins. Compilation of multibeam
bathymetry datasets collected by various primary sources over the last two
and half decades is accomplished using the multibeam processing software
package MB-System by Caress and Chayes (1996). The high-resolution product
is then employed to measure shape parameters of small seamounts (less than
1000 m). Methods of quantitative analysis established by Jordan et al. (1983)
and Smith (1988) are then used to assess the geomorphologic implications of
shape parameter relationships. These relationships suggest that morphologies
of small seamounts in American Samoa are typical of Pacific seamounts, though
infrequent departures show forms indicative mid-ocean ridge type magmas. A
distribution analysis of small seamounts follows, calculating areal density
with the exponential distribution model conceived by Jordan et al. (1983) and
modified by Smith and Jordan (1988). Distribution analysis yields a predicted
density of 2.8 seamounts per 1,000 km2 and a characteristic height of 139 m,
both within expectations for seamounts in the Pacific. Finally, a qualitative
interpretation of the entire study area is undertaken that includes mapping
of major volcanic features, morphologic descriptions of large seamounts, and
considerations of age-progression based on arrangements of volcanic lineaments.

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Thesis Defense

Publication of portions of M.S. thesis in a peer-reviewed book and in Geochemistry, Geophysics, Geosystems:

Wright, D.J., Roberts, J., Fenner, D., Smith, J.R., Koppers, A.A.P., Naar, D., Hirsch, E.R., Clift, L.W., and Hogrefe, K.R., Seamounts, ridges, and reef habitats of American Samoa, in Harris, P.T. and Baker, E.K. (eds.), Seafloor Geomorphology as Benthic Habitat: GeoHab Atlas of Seafloor Geomorphic Features and Benthic Habitats, Elsevier, Amsterdam, 791-806, 2012.

Koppers, A.A.P., Russell, J.A., Roberts, J., Jackson, M.G., Konter, J., Wright, D.J., Staudigel, H., and Hart, S.R., Age systematics of two en echelon Samoan volcanic trails, Geochemistry, Geophysics, Geosystems, 12, Q07025, doi:10.1029/2010GC003438, 2012.

Wright, D.J. and Roberts, J.T., Exploring the deeper reefs and volcanic provinces of American Samoa, ArcNews, 33(2): 18-19, 2011.

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