Monitoring Active Geologic Processes on the Alaska Margin

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Monitoring Active Geologic Processes on the
Alaska Margin

• What we know about the margin
• What we can add to our knowledge
• A starting point for monitoring

Margo Edwards, University of Hawaii (with L
Polyak, JL Engels, M Jakobsson, BJ Coakley)
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Broad Perspective

• Atlantic-type margin
• 75 km wide shelf
• shelf depth 0-50 m
• lt5º seaward dip of shelf
• down-to-the-north normal faults found near the
  shelf break
• bounded to the north by a steep, heavily
  canyoned continental slope that drops to 1000 mwd
  in the Canada Basin over 13 km

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SCICEX shows the devils in the details
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Iceberg Scours
Textures first, as seen on the Chukchi Cap
Water Depth lt 350 m
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Flutes
Water Depth 350 - 400 m
Chaotic Scours
Flutes 5 km field (N-S)
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Grounding Lines
Water Depth 350 - 400 m
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Seeps
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Glacigenic Features on Chukchi Margin
TWO sets of flutes on Chukchi Margin
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What about along the Alaska/Beaufort margin?
Figure courtesy of Okkonen and Weingartner
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SCICEX sidescan overview
Alaska/Beaufort Margin
N
H
G
A
B
C
D
E
F
Red boxes show areas with glacial
bedforms Iceberg scours Sub-glacial flutes
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Note pattern of bedforms
Glacial bedforms Bathymetric bench Gullies
N
A
5km
Area A Iceberg Scours/ Grooves
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Area C
Area C Iceberg Scours Glacial
bedforms Bathymetric bench Gullies
N
5km
C
13
Area E
N
Area E Flutes
5km
E
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Area G
Glacial bedforms Bathymetric bench Gullies
N
5km
Area G Flutes
G
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Fourier analysis of hi-res bathy
Gridded vs. full resolution bathymetry
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FFA results
Spacing and Severity of Seafloor Excavation
Scours/Grooves BROAD
Lineations NARROW
dB
A
H
H
H
H
H
H
H
H
H
H
H
G
G
E
c
b
b
b
A
West
East
WAVELENGTHS MAJORITY OF SEAFLOOR TOPOGRAPHY
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Bathymetric Bench profile
Bathymetric Bench sample profile
bench slope 1.6 surface roughness 25 m
IBCAO (m)
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Bathymetric Bench per IBCAO
Bathymetric Bench ABM generalization
IBCAO seafloor area in cumulative
percent (Jakobsson, 2003)
IBCAO (m)
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Gullies
Gullies Initiate at 500-700 mwd Dendritic
catchment areas gt10 km across Coalesce into
broad trunk channels Channel networks gt40 km
long Antarctic Norwegian- Greenland Sea
analogs Ice-marginal turbidites
N
10km
E
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MANY gullies
59 gullies/430 km Initiate at shelf
break Bench surface Slope 1.6 500-600
mwd Slope 10 600-700 mwd Slope 13
N
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What we can learn Recent mapping of ABM slope

• Larry Mayer UNH/NOAA
• SeaBeam 2112 data
• collected from USCG Healy
• October 2004

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SBI and other u/w HEALY data
Shelf-Basin Interaction (SBI) underway data
(HEALY Palmer)
Includes SB2112 multibeam plus Knudsen
Bathy2000 subbottom data for 5-6 field programs
from 2002-04. Also have HEALY data from ALTEX and
03 trip thru NW passage.
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So what are we looking for?

• Sediment transport
• Earthquakes
• Mass wasting and tsunami
• Seep-related deformation

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Gullies are preferred sediment pathways
Gullies Initiate at 500-700 mwd Dendritic
catchment areas gt10 km across Coalesce into
broad trunk channels Channel networks gt40 km
long Antarctic Norwegian- Greenland Sea
analogs Ice-marginal turbidites
N
10km
E
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Alaska also has earthquakes
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Other regions to monitor for earthquakes
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SCICEX survey of Lomonosov Ridge
showed evidence of mass wasting events
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Mass wasting on the Lomonosov
50 m contours
12 km
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A potential starting point - RUMBLEOMETER

• Bottom Pressure Recorder
• Short-Baseline Tilt Monitor
• Seismometer
• Electromagnetic Current Monitor
• Temperature Sensor