View
215
Download
2
Tags:
Embed Size (px)
Citation preview
The MARGINS Program“To understand the complex interplay of processes that govern the evolution of
continental margins”
MARGINS has four themes:Rupturing Continental Lithosphere,Seismogenic Zone,Subduction Factory, and
SOURCE TO SINK
Writing Earth history with continental-margin sedimentary processes
WRITING EARTH HISTORY WITH CONTINENTAL-MARGIN
SEDIMENTARY PROCESSES
Jantang, Sumatra
Courtesy of H. Higman
Photo: Brian AtwaterCourtesy of Brian Atwater
41o00’
40o50’
40o40’
124o40’ 124o30’
700
600
500
400
350
300
250 20
015
0 100
9080
7060
5040
302 0
10
Eel River Drainage BasinEel River Drainage Basin
Eel River Drainage Basin~9000 km2
Study Area
0 m
350
1400
Elevation
CaliforniaEel margin
Courtesy of Jeff Borgeld
Wheatcroft and Borgeld, 2000
Fingerprint of Flood Sedimentation on the Eel Shelf
(Sommerfield et al., 1999)
Sommerfield et al., 2007
41 º 00 '
40 º 50 '
40 º 40 '
40 º 30 '1 24 º 40 ' 1 24 º 30 ' 1 24 º 20 ' 1 24 º 10 '
700
50 20 1 0
S tudy area
Ee l C a ny on
H umb oldtB ay
Eel R iv er
M adR iv er
2
4
68
S 60
TRIPOD
MOORING
Location of observations in Eel Canyon
Eel Canyon Morphology
Complex channel shape makes placement of sediment cores difficult
Sedimentary fingerprints indicates that flood sediments are entering
submarine canyon
Southeast Alaska Coast
Sediment supplied from glacier-fed rivers
Courtesy of John Jaeger
Surge events from Bering Glacier recorded on adjacent shelf
Courtesy of John Jaeger
Courtesy of Peter Harris
Modern Coastal Rivers
Courtesy of Bill Dietrich
Obo
From Lui et al. (2003)
NORTHERN ADRIATIC SEA
Po River
ITALY
CROATIA
Ancona Promontory
Gargano Peninsula
Apennine Mountains
Venice Lagoon
abandonment of Po di Primaro 1152 AD a major natural avulsion northward shifting of distributary channels Venice Republic is threatened by the
potential infilling of the lagoon
1604 AD digging of a diversionary canal (Taglio di porto Viro)
The artificial form of the modern delta
NORTHERN ADRIATIC SEA
Po River
ITALY
CROATIA
Ancona Promontory
Gargano Peninsula
Apennine Mountains
Venice Lagoon
History of Apennine sediment discharge
Excess 210Pb Activity (dpm/g)
0
50
100
150
200
250
1.0 10.0
Supported = 0.7
0.1
11.2 mm/yR2 = 0.72
15.0 mm/yR2 = 0.97
7.80 mm/yR2 = 0.89
Tronto River
9.7 mm/y
3.2 mm/y
Eel RiverSangro River
0
50
100
150
200
2501.0 10.0
Excess 210Pb Activity (dpm/g)
0.1
10.2 mm/yR2 = 0.68
15.4 mm/yR2 = 0.96
6.58 mm/yR2 = 0.97
(KS02-30) (KS02-355)
Dams reduce sediment accumulation in Adriatic Sea
Clearcutting increases sediment load
Dams reduce sediment load
DAMS WIN
Sediment source for
southern WA coast
beaches
Dams placed on Columbia River during 20th century likely trapped much sediment
Greatest impact reached the coast in ~1980, after lower river was flushed
Ocean waves andcurrents transport sediment northward, distributing it along beach and continental shelf
Coast of Washington State
Southwest Washington Erosion Study
Changes in Wave Climate
(Allan and Komar, 2001)
Coastal erosion has caused loss of structures and roads
And has led to hardening of the shoreline in some places
Mississippi Delta
Historically has provided coastal protection to New Orleans
Bird-foot delta
Sedimentation extends to shelf break
List of some things we did
Dammed river – reduced sediment supply, 400 million t/y to 200 t/y
Built artificial levees – reduced nourishment of flood plain
Prevented lobe switching – reduced sediment supply to other parts of delta plain (30% to Atchafalaya)
Constrained flow to modern delta – caused delta to build to shelf break, and lose sediment to continental slope
Removed water and natural gas – accelerated consolidation of deltaic sediment and subsidence of land surface
Dredged channels – created depressions that act as sediment traps and water conduits
Writing Earth history with continental-margin sedimentary processes
IF WE DON’T LEARN FROM HISTORY, WE’RE DOOMED TO
RELIVE IT
% Sand Comparison
% Sand 2005
0 20 40 60 80 100
% S
and
1975
/197
6
0
20
40
60
80
100
Trees are ripped out of hills to an elevation of >30 m by thetsunami in Sumatra (just south of Lho Nga)
Courtesy of H. Higman
Tsunami transported bridge at Jantang, Aceh (Sumatra)
2/27/99