Morphological Interpretation of Seamounts in American Samoa: Inferring Genesis Mechanisms through Shape and Distribution Analysis Morphological Interpretation

Morphological Interpretation of

Seamounts in American Samoa:

Inferring Genesis Mechanisms through Shape and Distribution Analysis

Morphological Interpretation of

Seamounts in American Samoa:

Inferring Genesis Mechanisms through Shape and Distribution Analysis

Jed RobertsMaster’s Candidate in Geography

Department of Geosciences

Oregon State University

AAG San Francisco - April 19, 2007

Jed RobertsMaster’s Candidate in Geography

Department of Geosciences

Oregon State University

AAG San Francisco - April 19, 2007

Presentation OverviewPresentation Overview

Study Area

Research Questions

Data Description

Shape Statistics

Distribution Analysis

Morphological Interpretation

Future Work

Acknowledgements

Image produced by the U.S. National Park Service

Study AreaStudy Area

Study AreaStudy Area

Eastern Volcanic Province(American Samoa)

Western Volcanic Province(Samoa)

Image produced by the U.S. National Park Service

Why This Study Area?Why This Study Area?

Data availability

Intrigue of controversy regarding volcanic regime

No previous comprehensive investigation of

geomorphology in the eastern volcanic province

Tectonic SettingTectonic Setting

Image modified from Sandwell and Smith

ControversyControversy

Artwork by Jayne Doucette, Woods Hole

Oceanographic Institution

Artwork by Naoto Hirano, Scripps Institution of Oceanography

Hart et al. suggest primary

volcanic mechanism is a mantle plume

(hotspot)

Natland suggests lithospheric flexure at plate boundary results in shallow magma upwelling

Research QuestionsResearch Questions

Will shape and distribution analyses reveal new clues about seamount

origin in the absence of corresponding geochemical data?

Will the findings support one volcanic regime, both, or neither?

How will predicted seamount distributions compare with previous

studies?

Data DescriptionData Description

Multiple datasets collected during separate research cruises (1999-2005)

Cruises operated by Scripps Institution of Oceanography, HURL, Oregon State

University, and University of South Florida

Data collected by various shipboard multibeam sonar systems with differing

quality

Data has been merged at a resolution of 210m with depths of up to 6 km below sea level covering an area of 27,181 square km

Multibeam DataMultibeam DataMerged with Sandwell and Smith 1km resolution predicted bathymetry

Image created using FledermausData source: The Seamount Catalog

www.earthref.org

Multibeam DataMultibeam DataWith 210m resolution swaths isolated

Image created using FledermausData source: The Seamount Catalog

www.earthref.org

Methods | Identifying Seamounts


Create slope surface for multibeam data

Candidate seamounts are visually circumscribed by slope

Avoid island and large seamount flanks, select seamounts near or on abyssal plain

100 meters or more in height, due to resolution constraints

Completeness of data

Map created in FledermausData source: The Seamount Catalog

www.earthref.org


Methods | Identifying SeamountsSlope Surface


www.earthref.org


Methods | Identifying Seamounts51 Seamounts Selected

Assume an elliptical base and summit

Approximate seamount shape as a conical frustum

Methods | Characterizing Seamounts


Images created in Fledermaus



Cross-sectional View

Plan View

Slope Left

Base Width

Slope Right

Summit Width

Height

Images created in Fledermaus



Base Depth

Azimuth Angle

Base and Summit Areas

Height

Slope

Base Depth

Flatness (ratio of summit to base area)

Elongation (ratio of base minor axis to base major axis)

Volume

Methods | Seamount Statistics

Methods | Seamount Statistics

Results | Seamount Statistics

Results | Seamount Statistics

-------------------------

MeanSt. Dev.

Min. Max. Total

Base Area (km2) 6.7633 5.58001.7064

36.5213344.9299

Summit Area (km2)

0.0891 0.28280.0044

2.0487 4.5453

Height (m) 323 152 105 850 N/A

Slope (%) 13.3 3.3 5.9 19.7 N/A

Base Depth (mbsl)

-4245 738 -2640 -5380 N/A

Flatness 0.0118 0.01610.0014

0.1021 N/A

Elongation 1.28 0.24 1.00 2.10 N/A

Volume (km3) 1.01 1.58 0.09 10.76 51.73

Results | Relational Statistics
















Methods | Distribution Analysis


Negative Exponential Distribution

(from Smith and Jordan [1988])

Distribution of seamounts is modeled as:

v(H) = v0exp(-ßH)Where v(H) is the # of seamounts per unit area with a height greater than H, v0 is the total # of seamounts

per unit area, and ß is the negative of the slope of the line fitting ln(v(H)) against H

The characteristic height of the seamount sample is equal to negative

reciprocal of ß

Define appropriate sample

100 meter height bins containing at least three seamounts were included

48 seamounts in all, within 100-600 meter height range

Define appropriate areal value

Total area of data set is 27,181 km2

Reduced to 22,745 km2 by including only depths below -2640 m

This area approximates only the near-lithosphere abyssal plain





100-600 m range100-600 m range

Define appropriate sample

100 meter height bins containing at least three seamounts were included

48 seamounts in all, within 100-600 meter height range

Define appropriate areal value

Total area of data set is 27,181 km2

Reduced to 22,745 km2 by including only depths below -2640 m

This area approximates only the near-lithosphere abyssal plain




www.earthref.org

Calculation of Area by -2640 m Cutoff

Total area before depth cutoff: 27,181 km2

Total area before depth cutoff: 27,181 km2



Total area after depth cutoff: 22,745 km2

Results | Distribution Analysis


νν00 = 2.6 ± 0.2 = 2.6 ± 0.2 (per 1000 (per 1000

kmkm22))

ßß-1 -1 = 138 m= 138 m

νν00 = 2.6 ± 0.2 = 2.6 ± 0.2 (per 1000 (per 1000

kmkm22))

ßß-1 -1 = 138 m= 138 m


Results | Distribution AnalysisComparison with previous studies

Study Region (Latitude)

Height Range (m)

Seamount Density (per 103 km2) [v0]

Characteristic Height (m) [ß-1]

This Study ASSC (13º-15ºS) 100 – 600 2.6 ± 0.2 138

Jaroslow et al. (2000) MAR (25º-27ºN) 70 – 350 58.3 ± 1.6 92

Rappaport et al. (1997) ESC (27º-29ºS) 200 – 1000 2.7 ± 1.5 308

Schierer et al. (1996) Southern EPR (15º-19ºS)

200 – 1200 4.8 ± 0.2 421

Magde and Smith (1995) Northern MAR (57º-62ºN)

50 – 250 310 ± 20 68

Schierer and MacDonald (1995)

Northern EPR (8º-18ºS) 200 – 800 1.9 ± 0.2 240

Kleinrock and Brooks (1994)

Galapagos (2ºN, 95ºW) 50 – 350 370 ± 30 29

Bemis and Smith (1993) Southern Pacific (9º-22ºS)

300 – 700 13 ± 2 233

Smith and Cann (1990, 1992)

MAR (24º-30ºS) 50 – 210 195 ± 9 58

Abers et al. (1988) Southern Pacific (7º-22ºS)

100 – 1000 12.6 ± 0.8 174

Smith and Jordan (1987), and Smith (1988)

Eastern Pacific 400 – 2500 5.4 ± 0.7 285

ASSC is the American Samoa Seamount Chain, MAR is the Mid-Atlantic Ridge, ESC is the Easter Seamount Chain, EPR is the East Pacific RiseASSC is the American Samoa Seamount Chain, MAR is the Mid-Atlantic Ridge, ESC is the Easter Seamount Chain, EPR is the East Pacific Rise

Results | InterpretationResults | Interpretation

Relational shape statistics are in agreement with those observed in

previous studies

Elongation and azimuth reveal slight directional trends that may support

lithospheric flexure

Distribution analysis demonstrates seamount population densities typical

of southern Pacific

Small seamount chains trend northeast-southwest, while large

seamounts and islands trend east-west


www.earthref.org

Directional Trends

Results | InterpretationResults | Interpretation

SignificanceSignificance

Lithospheric flexure is not ruled out as volcanic mechanism for production of

small seamounts

Initial identification of seamounts

Volume and other shape statistics never before calculated

Locations and distribution of seamounts important for biological

studies and habitat protection

Future WorkFuture Work

Re-grid dataset at slightly higher resolution

Add data collected by NOAA in 2006 to regional dataset compilation

Examine shape statistics and distributions based on natural

geographic partitions

Submit seamount locations and morphologies to the Seamount Catalog

Compare findings with forthcoming geochronological data

AcknowledgementsAcknowledgementsDr. Dawn Wright, Oregon State

UniversityGraduate Advisor

Dr. Anthony Koppers, Oregon State University

Seamount Catalog Webmaster

Scripps Institution of Oceanography, Hawaii Undersea Research Lab, Oregon

State University, and University of South FloridaData Sources

Dr. Deborah Smith, Woods Hole Oceanographic Institution

Dr. Thomas Jordan, Massachusetts Institute of Technology

Distribution Analysis Methods

You can download this presentation here:http://oregonstate.edu/~robertje/projects/

aag2007

Contact me via e-mail at:[email protected].

edu

ReferencesReferencesAbers, G. A., Parsons, B., and Weissel, J. K. 1988. Seamount abundances and distributions in

the southeast Pacific. Earth and Planetary Science Letters. 87: 137-51.

Bemis, K. G., and Smith, D. K. 1993. Production of small volcanoes in the Superswell region of

the South Pacific. Earth and Planetary Science Letters. 118: 251-62.

Hart, S. R., Staudigel, H., Koppers, A. A. P., Blusztajn, J., Baker, E. T., Workman, R., Jackson, M.,

Hauri, E., Kurz, M., Sims, K., Fornari, D., Saal, A., and Lyons, S. 2000. Vailulu'u undersea volcano: The New Samoa. Geochemistry Geophysics Geosystems. 1(12): 2000GC000108.

Hart, S. R., Coetzee, M., Workman, R. K., Blusztajn, J., Johnson, K. T. M., Sinton, J. M., Steinberger, B., and Hawkins, J. W. 2004. Genesis of the Western Samoa seamount province: age, geochemical fingerprint and tectonics. Earth and Planetary Science Letters. 227: 37-56.

Hirano, N., Takahashi, E., Yamamoto, J., Abe, N., Ingle, S.P., Kaneoka, I., Hirata, T., Kimura, J.,

Ishii, T., Ogawa, Y., Machida, S., and Suyehiro, K. 2006. Volcanism in Response to Plate Flexure. Science. 313: 1426-28.

Jaroslow, G. E., Smith, D. K., and Tucholke, B. E. 2000. Record of seamount production and

off-axis evolution in the western North Atlantic Ocean, 25º25'-27º10'N. Journal of Geophysical Research. 105(B2): 2721-36.

Kleinrock, M. C., and Brooks, B. A. 1994. Construction and destruction of volcanic knobs at

the Cocos-Nazca spreading system near 95ºW. Geophysical Research Letters. 21(21): 2307-10.

Magde, L. S., and Smith, D. K. 1995. Seamount volcanism at the Reykjanes Ridge: Relationship to the Iceland hot spot. Journal of Geophyical Research. 100(B5):

8449-68.

ReferencesReferencesNatland, J. H. 1980. The progression of volcanism in the Samoan linear volcanic chain. American Journal of Science. 280-A: 709-35.

Natland, J. H. 2004. The Samoan Chain: A Shallow Lithospheric Fracture System. www.mantleplumes.org (last accessed March 11, 2006).

Rappaport, Y., Naar, D. F., Barton, C. C., Liu, Z. J., and Hey, R. N. 1997. Mophology and distrubution of seamounts surrounding Easter Island. Journal of Geophysical

Research. 102(B11): 24,713-28.

Scheirer, D. S., and Macdonald, K. C. 1995. Near-axis seamounts on the flanks of the East Pacific Rise, 8ºN to 17ºN. Journal of Geophysical Research. 100(B2): 2239-59.

Scheirer, D. S., MacDonald, K. C., Forsyth, D. W., and Shen, Y. 1996. Abundant Seamounts of

the Rano Rahi Seamount Field Near the Southern East Pacific Rise , 15º S to 19º S. Marine Geophysical Researches. 18: 13-52.

Smith, D. K. 1988. Shape analysis of Pacific seamounts. Earth and Planetary Science Letters.

90: 457-66.

Smith, D. K., and Jordan, T. H. 1988. Seamount Statistics in the Pacific Ocean. Journal of Geophysical Research. 93(B4): 2899-918.

Smith, D. K., and Cann, J. R. 1990. Hundreds of small volcanoes on the median valley floor of

the Mid-Atlantic Ridge at 24º-30º N. Nature. 348: 152-5.

Smith, D. K., and Cann, J. R. 1992. The Role of Seamount Volcanism in Crustal Construction at

the Mid-Atlantic Ridge (24º-30ºN). Journal of Geophyical Research. 97(B2): 1645-58.

ReferencesReferencesWalker, G. P. L., and Eyre, P. R. 1995. Dike complexes in American Samoa. Journal of

Volcanology and Geothermal Research. 69: 241-54.

Workman, R. K., Hart, S. R., Jackson, M., Regelous, M., Farley, K. A., Blusztajn, J., Kurz, M., and Staudigel, H. 2004. Recycles metasomatized lithosphere as the origin of the Enriched Mantle II (EM2) end-member: Evidence from the Samoan Volcanic Chain. Geochemistry Geophysics Geosystems. 5(4): 2003GC000623.

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Morphological Interpretation of Seamounts in American Samoa: Inferring Genesis Mechanisms through Shape and Distribution Analysis Morphological Interpretation