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