morphological interpretation of seamounts in american samoa: inferring genesis mechanisms through...
TRANSCRIPT
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
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 Seamounts
Methods | Identifying SeamountsSlope Surface
Map created in FledermausData source: The Seamount Catalog
www.earthref.org
Methods | Identifying Seamounts
Methods | Identifying Seamounts51 Seamounts Selected
Assume an elliptical base and summit
Approximate seamount shape as a conical frustum
Methods | Characterizing Seamounts
Methods | Characterizing Seamounts
Images created in Fledermaus
Methods | Characterizing Seamounts
Methods | Characterizing Seamounts
Cross-sectional View
Plan View
Slope Left
Base Width
Slope Right
Summit Width
Height
Images created in Fledermaus
Methods | Characterizing Seamounts
Methods | Characterizing Seamounts
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
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Results | Relational Statistics
Methods | Distribution Analysis
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
Methods | Distribution Analysis
Methods | Distribution Analysis
Methods | Distribution Analysis
Methods | Distribution Analysis
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
Methods | Distribution Analysis
Methods | Distribution Analysis
Map created in FledermausData source: The Seamount Catalog
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
Methods | Distribution Analysis
Methods | Distribution Analysis
Total area after depth cutoff: 22,745 km2
Results | Distribution Analysis
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 Analysis
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
Map created in FledermausData source: The Seamount Catalog
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.