Tufts Submarine Fan: 

Turbidity-Current Gateway to Escanaba Trough

By Jane A. Reid and William R. Normark

Bulletin 2216

U.S. Department of the Interior

U.S. Geological Survey
ii 

U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2003

U.S. Geological Survey Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

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Published in the Western Region, Menlo Park, California

Manuscript approved for publication, September 26, 2003

Text edited by Peter H. Stauffer

Production and design by Susan Mayfield
iii

Contents

Abstract 1

Introduction 1

Data 2

Cascadia Channel and Tufts Submarine Fan 2

Cascadia Channel 2

Tufts Fan 3

Discussion 5

Age of Tufts Fan 5

Tufts Fan Elements and Tufts Abyssal Plain 6

Conclusions 6

References 7

Tables

1. Key turbidite beds in Escanaba Trough and water depth (top of flow) at the time of 

deposition of each bed 9

2. Locations of cores with evidence for glacial Lake Missoula deposits 9

Figures

1. Schematic map showing path of late Pleistocene glacial flood sediment from the 

Columbia River mouth to the Tufts fan, Escanaba Trough, and Tufts Abyssal Plain 10

2. Map and acoustic backscatter mosaic of the study area 11

3. Deep-tow 4.5-kHz high-resolution reflection profile showing the characteristic spacing 

of the turbidite reflector sequence (A to I) in Escanaba Trough at ODP Hole 1037B 13

4. Single-channel, airgun seismic-reflection profiles crossing Cascadia Channel 14

5. Seismic-reflection profiles across the upper Tufts fan 15

6. Seismic-reflection profiles in overflow areas adjacent to the Cascadia Channel and 

upper Tufts fan, showing extensive ponding of sediment from turbidity currents 16

7. Seismic-reflection profiles across the middle and lower fan areas of Tufts fan 17

8. High-resolution 3.5-kHz reflection profiles with evidence of flow stripping adjacent to 

the Tufts fan 18

9. GLORIA sidescan-sonar backscatter image of the upper, middle, and lower Tufts fan 

and of the Tufts fan channel 19

10. GLORIA sidescan-sonar backscatter image of the sea floor immediately north of the 

Mendocino Fracture Zone along the pathway of turbidity currents that flowed into 

Escanaba Trough 20

11. Single-channel, airgun seismic-reflection profiles showing extensive ponding of sediment from turbidity currents in the area north of Mendocino Fracture Zone (MFZ) 21

12. Seismic-reflection profiles across the southern end of Escanaba Trough (parallel to the 

Mendocino Fracture Zone, [MFZ]) 22

13. Acoustic-facies interpretation of the Tufts fan and areas with flow-stripped and 

trapped turbidite sediment 23
Abstract

Turbidity-current overflow from Cascadia Channel 

near its western exit from the Blanco Fracture Zone has 

formed the Tufts submarine fan, which extends more than 

350 km south on the Pacific Plate to the Mendocino Fracture Zone. For this study, available 3.5-kHz high-resolution 

and airgun seismic-reflection data, long-range side-scan 

sonar images, and sediment core data are used to define the 

growth pattern of the fan. Tufts fan deposits have smoothed 

and filled in the linear ridge-and-valley relief over an 

area exceeding 23,000 km2 on the west flank of the Gorda 

Ridge. The southernmost part of the fan is represented by 

a thick (as much as 500 m) sequence of turbidite deposits 

ponded along more than 100 km of the northern flank of 

the Mendocino Fracture Zone. Growth of the Tufts fan now 

permits turbidity-current overflow from Cascadia Channel 

to reach the Escanaba Trough, a deep rift valley along the 

southern axis of the Gorda Ridge. 

Scientific drilling during both the Deep Sea Drilling 

Project (DSDP) and the Ocean Drilling Program (ODP) 

provided evidence that the 500-m-thick sediment fill of 

Escanaba Trough is dominantly sandy turbidites. Radiocarbon dating of the sediment at ODP Site 1037 showed that 

deposition of most of the upper 120 m of fill was coincident 

with Lake Missoula floods and that the provenance of the 

fill is from the eastern Columbia River drainage basin. The 

Lake Missoula flood discharge with its entrained sediment 

continued flowing downslope upon reaching the ocean as 

hyperpycnally generated turbidity currents. These huge turbidity currents followed the Cascadia Channel to reach the 

Pacific Plate, where overbank flow provided a significant 

volume of sediment on Tufts fan and in Escanaba Trough. 

Tufts fan and Tufts Abyssal Plain to the west probably 

received turbidite sediment from the Cascadia margin during much of the Pleistocene.

Introduction

Most modern submarine fans receive sediment as a result of 

a direct connection to an adjacent submarine canyon or large 

river delta and thus are found immediately adjacent to continental areas (for example, Bouma and others, 1985). The Tufts 

fan, in contrast, has formed on the Pacific Plate some 400 km 

off the Oregon and northern California coast and is separated 

from the North American continent by the Gorda Ridge, a 

high-relief, oceanic spreading center (fig. 1). The Tufts fan 

receives sediment from the Cascadia deep-sea channel, which 

itself is atypical of submarine turbidite pathways. The Cascadia Channel reaches the Pacific Plate via a narrow trough in 

the Blanco Fracture Zone and continues west for more than 

1,000 km (figs. 1, 2; see Hurley, 1964; Griggs and Kulm, 

1970a; Embley, 1985; DeCharon, 1986).

 The character of the sediment transported through and 

deposited in Cascadia Channel is generally known from 

samples obtained mostly on the eastern side of the oceanic 

ridge system (Duncan and others, 1970; Duncan and Kulm, 

1970; Griggs and Kulm, 1970b, 1973). One study (Griggs and 

others, 1970) specifically suggested, however, that sediment 

from the late Pleistocene floods from glacial Lake Missoula 

reached the Pacific Plate through Cascadia Channel. 

Escanaba Trough, the turbidite-covered southernmost 

segment of the Gorda Ridge axial valley, lies 300 km to the 

south of Cascadia Channel and just north of the Mendocino 

Fracture Zone (fig. 1). Sediment recovered at Deep Sea 

Drilling Program (DSDP) Site 35 within Escanaba Trough 

indicated that the upper few hundred meters of this sediment 

fill probably came from the Columbia River drainage area 

(Shipboard Scientific Party, 1970; Vallier, 1970; Vallier and 

others, 1973; Zuffa and others, 1997). Later drilling during 

Ocean Drilling Program (ODP) Leg 169 provided a continuously cored section to basaltic basement at more than 500 m 

subbottom (Shipboard Scientific Party, 1998). Zuffa and others 

(2000) determined that the bulk of the fill of Escanaba Trough 

recovered at ODP Site 1037 is from the Columbia River and 

not the adjacent California margin (fig. 1). Zuffa and others 

(2000) suggested that the Lake Missoula floods generated 

turbidity currents as a result of hyperpycnal flow upon reaching the ocean because of the tremendous amount of sediment 

carried in the floods (see Mulder and Syvitski, 1995). These 

Tufts Submarine Fan: 

Turbidity-Current Gateway to Escanaba Trough

1

Santa Cruz, California

2

Menlo Park, California

By Jane A. Reid1 and William R. Normark2
2 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

workers further suggested that the sediment must have reached 

Escanaba Trough from the Pacific Plate because an enormous 

submarine slide that occurred about 110 ka, the Heceta slide, 

blocked southward transport of sediment along the base of the 

continental slope south of central Oregon (fig. 1; Goldfinger 

and others, 2000).

Evidence for the latest Pleistocene (that is, glacial Lake 

Missoula) catastrophic floods in the northwestern United 

States and southwestern Canada is abundant (see, for example, 

Bretz and others, 1956; Atwater, 1986; Baker, 1973; Baker and 

Bunker, 1985; Shaw and others, 1999; Waitt, 1980, 1985). On 

the other hand, the fate of these flood discharges after reaching 

the mouth of the Columbia River has remained largely undefined. The purpose of this study is to review the development 

of the informally named Tufts fan and evaluate the role of that 

fan in providing a Pacific Plate pathway for the glacial Lake 

Missoula flood deposits that reached Escanaba Trough.

Data

The Tufts fan study is primarily based on archive data 

obtained during the 1980s as part of the U.S. Geological 

Survey (USGS) sea-floor hydrothermal mineral project and 

surveys of the U.S. Exclusive Economic Zone (EEZ). Much 

of the fan area was surveyed to the limit of the 200-nauticalmile (370 km) EEZ during the GLORIA (Geological Long 

Range Inclined ASDIC) surveys of 1984 (EEZSCAN 84 

Scientific Staff, 1986). In addition to the GLORIA side-looking sonar image of the sea floor, the surveys also obtained 

airgun seismic-reflection profiles and high-resolution 3.5-kHz 

profiles along regularly spaced, east-west tracklines (fig. 2A). 

A multichannel seismic-reflection survey of the southern Juan 

de Fuca and southern Gorda Ridges also obtained 3.5-kHz 

seismic-reflection profiles. Vessel transits to and from the 

southern Juan de Fuca Ridge in support of the USGS hydrothermal mineral program obtained only 3.5 kHz profiles. 

These tracklines form a narrow fan-shaped spread with the 

apex just north of the study area for this paper (fig. 2A); the 

higher speed during these transit legs resulted in large vertical 

exaggeration in these profiles.

More than 4,000 line kilometers of seismic-reflection 

data from nine expeditions conducted between 1980 and 

1985 were available for this study, with position control for 

all cruises based on transit satellite data. A limited number of 

sediment-core samples from around the area of Tufts fan were 

obtained during earlier studies by Oregon State University 

researchers, and these confirm widespread deposition of terrigenous sediment of latest Pleistocene age on the west flank of 

the Gorda Ridge (fig. 2A). The significance for understanding 

the development of Tufts fan is provided by USGS-collected, 

unpublished deep-tow 4.5-kHz profiles acquired in support 

of ODP Leg 169 and subsequent drilling at Site 1037 in the 

Escanaba Trough (Shipboard Scientific Party, 1998). The 

continuously cored sequence obtained at this site was used 

to provide ground truth for interpretation of the high-resolution seismic-reflection data (Zuffa and others, 2000). A key 

sequence of 11 turbidite beds sampled in the upper 63 m of 

the hole is found throughout Escanaba Trough in water depths 

greater than 3100 m (figs. 1,3; table 1; Zuffa and others, 2000; 

Normark and Serra, 2001). 

Escanaba Trough is a dead end for all turbidity currents 

that flow into it; as a result, all of the sediment in suspension 

within the turbidity-current flows is deposited, resulting in 

thick beds that show the same relative spacing of reflectors 

throughout the Trough. The thickness of any given turbidite 

bed in Escanaba Trough is a function of the water depth at 

the time of deposition (Normark and others, 1997; Normark 

and Serra, 2001). This relationship reflects the decreasing 

volume of suspended sediment with increasing height above 

the base of the flow. Except where the turbidity currents 

are trapped in closed basins such as Escanaba Trough, their 

appearance on high-resolution seismic-reflection records (the 

acoustic facies) is common to modern deep-sea fans everywhere. The difference in acoustic character between deposits 

resulting from trapped flow and those left during the passage 

of a turbidity current can be used to understand the growth 

pattern of Tufts fan.

Cascadia Channel and Tufts 

Submarine Fan

Tufts submarine fan is a relatively small deposit that has 

formed as a consequence of the transport of a tremendous volume of sediment to the Pacific Plate via the Cascadia Channel. 

Hurley (1960) recognized the importance of Cascadia Channel, but surprisingly little has been done since his pioneering 

work to map the extensive terrigenous deposits in the northeast 

Pacific Ocean (see review of Stevenson and Embley, 1987). 

The relation between Cascadia Channel, Tufts fan, and the 

glacial Lake Missoula floods is examined in this section.

Cascadia Channel

Cascadia Channel extends from offshore of the Willapa 

Canyon near the mouth of the Columbia River (fig. 1). Hurley 

(1964) showed that the channel extends about 2,300 km from 

the base of the continental slope. Later work, however, has 

generally been limited to the proximal 700 km of the channel, that is, to the area upstream from where the channel exits 

the Blanco Fracture Zone (BFZ) (Griggs and Kulm, 1970a, 

b; 1973; Embley, 1985). As Cascadia Channel bends to the 

south toward its interception with the BFZ, the channel forms 

the western margin of the Astoria Fan, acting as a drainage 

channel for flows that move across the fan (fig. 1). Cascadia 

Channel is deeply eroded where it approaches the BFZ (fig. 

4A). Available crossings of the channel show that it is 200–300 

m deep throughout the study area, except in the BFZ, where 

it is only slightly less deep (Embley, 1985; fig. 4B). Embley 

(1985) obtained multibeam sounding data that showed that the 
Cascadia Channel and Tufts Submarine Fan 3

Cascadia Channel makes abrupt, nearly 90° bends not only 

where it enters and exits the BFZ, but also where it steps from 

the northern to the southern side of the fracture-zone trough 

(figs. 1, 2).

The seismic-reflection profiles of figure 4 show that both 

north and south of the BFZ, the Cascadia Channel is eroded 

into stratified, generally flat-lying deposits that have an acoustic character typical of turbidite deposition. The right-hand 

margin of the channel is higher than the left on all crossings; 

however, distinct levee relief is exhibited in only a few places, 

for example in figs 4B, D. Elsewhere, overflow near the channel has been of sufficient volume to smooth the underlying 

relief of the sea floor, ponding between volcanic hills and 

ridges (fig. 4A, west side). All of the available seismic-reflection profiles show that the upper part of the stratified sediment 

along the margins on both sides of the Cascadia Channel has 

smoothed pre-existing topography, whether of autocyclic origin or pre-existing basement topography (figs 4, 5A, B, 6A, C).

Where Cascadia Channel has sharp bends, the upper 

part of a turbidity current that exceeds the channel depth will 

continue to flow uninhibited by the bend. This process is 

known as flow stripping, because the upper part of the turbidity current is separated from the flow remaining in the channel 

(Piper and Normark, 1983), and is a special case of overbank 

deposition around turbidite channels. Tufts fan receives flowstripped sediment in the area immediately south of the sharp, 

westward bend in the channel that is downstream from its exit 

from BFZ. In this area, there is a low, convex-upward profile 

of the fan surface (figs 5A, B). Slightly farther west, deposits 

of normal overbank flow that also feeds Tufts fan have generally smooth, flat-lying appearance (see, for example, fig. 4C). 

Upstream from Tufts fan, where the Cascadia Channel 

turns south to exit the BFZ, westward-directed flow stripping 

removed substantial volumes of sediment from the flows, 

even though the channel has nearly 300 m of relief along its 

right-hand margin. In total, this westward-directed flow-stripping action deposited as much as 500 m of turbidites in a 

deep, 100-km-long trough on the southwest side of the BFZ 

(fig. 6A) and filled other smaller basins in the rugged topography between the channel and BFZ. Both the airgun and 

3.5-kHz high-resolution profiles across these basins filled by 

flow-stripped deposits show that sea-floor relief produced by 

tectonic deformation has been nearly eliminated by the ponded 

deposits (figs 6A, B). The present sea-floor water depths of 

these overbank turbidite deposits north and west of Cascadia 

Channel generally are between 3,150 and 3,275 m. The upper 

surfaces of the larger turbidity currents, where recorded in 

Escanaba Trough, are generally between 3,125 and 3,194 m 

water depth (table 1); thus, the ponded turbidites north of the 

channel appear well within the depth range of the flows that 

reached Escanaba Trough.

To understand the extent of deposition from the turbidity 

currents that were generated by the larger floods from glacial 

Lake Missoula, the figures presenting reflection profiles show 

the range in depths to the tops of the turbidity currents that 

reached Escanaba Trough (for example, fig. 4; table 1). North 

of the BFZ, the turbidity currents from the floods probably 

flowed across much of Astoria Fan and overflowed Cascadia 

Channel to smooth the sea floor west of the channel (fig. 4A). 

Once the currents descended into the BFZ, however, the flows 

became confined until reaching the area of Tufts fan and the 

elongate basins adjacent to the main trend of the BFZ. 

Deposition within Cascadia Channel is typical of many 

modern turbidite systems, showing a change to more clayrich sediment during the Holocene (Griggs and Kulm, 1970b, 

1973). Nelson and others (1988) were able to use the presence 

of Mazama ash, dated at 7.7 ka, in several sandy turbidite beds 

within the sequence in Cascadia Channel to demonstrate that 

the channel was active well into the mid Holocene. There is a 

marked change in sediment grain size, however, between the 

late Pleistocene and Holocene deposits in Cascadia Channel. 

Griggs and others (1970) described coarse-grained (to gravel 

size) sediment from three localities within the proximal 750 

km of Cascadia Channel. One sample, core C3, was from the 

channel on the south side of the BFZ (table 2 and fig. 2A). 

Griggs and others (1970) showed that the lithology of pebbles 

in these gravel beds is consistent with rock types known from 

the drainage basin of the Columbia River and its tributaries. 

Conclusive ages for the gravel layers were not available, but 

the authors speculated that the deposits were brought to the 

ocean by late Pleistocene glacial floods.

Other core samples on the north side of Cascadia Channel document that terrigenous-sediment deposition occurred 

in the same time frame as the Lake Missoula floods. Core C1 

(table 2 and fig. 2A) recovered 9.75 m of inferred late Pleistocene terrigenous sediment at 3,232-m water depth in the area 

of flow-stripped deposition that lies 50 km west of the exit 

of Cascadia Channel from BFZ (Duncan and others, 1970). 

Carbon-14 analyses gave an age of 15.9 ka at 2.3-m depth 

in this core. At 5.8 m depth in the core, the age was 27.2 ka, 

suggesting deposition of terrigenous sediment earlier than the 

the Lake Missoula floods. Core C2 (table 2 and fig. 2A), which 

is from Cascadia Channel on the Pacific Plate about 20 km 

west of the channel-floor core described by Griggs and others 

(1970), shows that turbidite deposition was common until just 

after 9.6 ka; this is consistent with the age of the youngest 

turbidite cored at ODP Site 1037 in Escanaba Trough (Duncan 

and others, 1970; Brunner and others, 1999).

 Tufts Fan

Tufts fan is defined herein as the turbidite system that 

extends southwards from Cascadia Channel immediately 

downstream of its exit from the BFZ (fig. 2). Its name is taken 

from the adjacent Tufts Abyssal Plain, a name which has been 

used to cover all of the terrigenous-sediment-covered area 

west of the Gorda Ridge (Hurley, 1960).

The Tufts fan is fed by overbank flow where the Cascadia Channel turns abruptly west after reaching the Pacific 

Plate (figs. 2, 5). The southern wall of the Cascadia Channel 

is about 150 m above its thalweg at this bend (fig. 4C), with 

the water depth along this southern overbank area at between 
4 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

3,260 and 3,300 m. Thus, as shown by the depth to the tops of 

the turbidity currents that reached Escanaba Trough (table 1), 

the larger turbidity currents moving through Cascadia Channel 

could overflow along a 40-km-long reach of the channel. 

The elongate shape of Tufts fan is a result of allocyclic 

control by bedrock topography on the flow of turbidity currents building the system. The linear ridge-and-valley topography of the flank of Gorda Ridge is clearly shown where the 

tops of the ridges have not yet been buried by fan sediment 

(fig. 2B). Tufts fan does not exhibit a simple apex because it 

does not have a point source, such as a submarine canyon, for 

sediment building the fan. Rather, the overflow from Cascadia 

Channel occurs along a reach of as much as 50 km, depending on the thickness of the flow after it exits from the Blanco 

Fracture Zone (figs 1, 2B). Thus, upper Tufts fan is primarily 

an overbank (levee) deposit for Cascadia Channel and shows a 

typical autocyclic morphology indicative of both overbank and 

upper fan elements.

The eastern edge of the fan generally trends north–south 

and is characterized by turbidite deposition onlapping and 

ponding between basement ridges on the flank of the Gorda 

Ridge. The western edge of the fan is bounded by prominent 

north-south-trending ridges, except between about 42° and 

42°45’ N latitude, where bathymetric data are insufficient to 

resolve the fan boundary (fig. 2A).

As noted above, Tufts fan is fed by both flow-stripping 

and normal overbank deposition. As a result, the upper fan 

does not show typical turbidite channel/levee relief that is 

found on submarine fans fed by canyons or deltas. An area of 

convex-upward morphology is the equivalent of an upper fan 

environment for Tufts fan, with the total turbidite sediment 

thickness typically 200 to 300 m in this area (fig. 5A). A broad, 

low-relief, southward-directed feeder channel nearly due 

south of Cascadia Channel’s exit from the BFZ is evident on 

both deep- and shallow-penetrating seismic lines (fig. 5B, C). 

This channel on the upper fan shows well-developed sediment 

waves on the western (right-hand, looking downstream) levee 

that are at a scale typical for overbank deposition on the upper 

part of many submarine fans (Wynn and Stow, 2002; Normark 

and others, 2002). Much of the broad, convex-upward relief on 

the Tufts fan is the result of the formation of the western levee 

of the channel. The eastern levee, in contrast, is narrower and 

its form might in part reflect allocyclic control on deposition. 

The upper fan area east of the channel levee feature is generally flat as a result of ponding in a basin south of a high ridge 

of the BFZ (figs. 2B 6C, D). The western upper fan is gently 

sloping with little local relief (see, for example, fig. 4C). This 

low relief probably reflects the ponding of flows caused by the 

north-south trending ridges that form the western margin of 

the upper fan (fig. 2B).

From the southern edge of the upper fan at about 43° 15’ 

N to the Mendocino Fracture Zone (MFZ), 300 km farther 

south, the turbidite deposits are ponded between the numerous 

basement ridges and hills on the flank of Gorda Ridge (figs. 2, 

7-11). Numerous small channels on the surface of the fan similar to those found on lobe areas of sandy submarine fans (fig. 

7A, B; Piper and Normark, 2001) mark the northern portion of 

the middle fan. These small channel features are limited to the 

area between the smooth convex-upward morphology of the 

upper fan and about 42°45’ N latitude (fig. 9). Several scour 

features or moats are evident around small ridges and hills, 

where acceleration occurs as the flows impinge upon the topographic restriction. Flows were probably confined between 

north-south ridges, which were progressively buried by successive large turbidity currents. The channelized/scoured lobe 

area (middle fan) of Tufts fan shows typical turbidite character 

in 3.5-kHz profiles, with relatively high-amplitude, continuous, and subparallel reflectors (figs. 7A, B, 9). 

The GLORIA sidescan-sonar backscatter image of 

figure 9 shows the transition from the channelized middlefan area to the sloping lower-fan element where low-relief 

lobes are found. The ridges that form the eastern and western 

margins of the fan show as light (high backscatter) returns in 

the GLORIA image. Channel and depositional-lobe elements 

are observed locally but are relatively subtle features in this 

image compared with GLORIA images from the distal Mississippi Fan (see figs. 5-10A in Twichell and others, 1996). 

The backscatter image of Tufts middle fan shows no prominent continuous channels that might serve as major conduits 

for turbidity currents flowing south. This lack of surficial 

channel features is consistent with deposition over the entire 

fan surface from the largest flows resulting from glacial Lake 

Missoula floods. The depth of the upper surface of these 

flows indicates that the entire fan surface shown in figure 9 

was covered by the flows.

More prominent in the backscatter image of figure 9 are 

the deeper, isolated pockets of ponded sediment along the 

eastern margin of Tufts fan that show an acoustic character 

similar to the latest Pleistocene deposits in Escanaba Trough 

(fig. 10). Where the seismic-reflection profiles and 3.5-kHz 

profiles cross an isolated pocket of sediment characterized by 

widely spaced, parallel reflections (fig. 8; compare acoustic 

character with fig. 3), the backscatter image shows the lowest 

strength (black) returns (figs. 2B, 9, 10). In all cases, these 

deeper, local basin-fills are separated from Tufts fan by one or 

more ridges (figs 2B, 8). These local basins most likely filled 

by the deposits stripped from the upper part of flows that have 

overtopped the ridge crests while the main body of the flows 

continued to the south.

The lower-fan and basin-plain elements, which make 

up much of Tufts fan, are broken into north-south-trending 

turbidity-current pathways separated by the partially buried (north-south-trending) ridges on the Gorda Ridge flank 

(figs. 2A, 10). These two fan elements are between 3,275 

and 3,350 m water depth, which is deeper than the observed 

flow-stripped deposits north of the Cascadia Channel. On the 

gently sloping lower fan and basin plain, onlap of the subparallel reflections on the tops of basement ridges is commonly 

observed (fig. 7D). The reflection character of the lower fan 

and of the distal eastern margin of the upper fan approaches 

that of the isolated, local basin fills described above (compare figs. 6D and 7D with fig. 8).
Discussion 5

Where the Tufts fan impinges upon the high relief of the 

MFZ, more than 500 m of mostly turbidite sediment fills a 

trough at the base of the ridge (figs. 10, 11). Thick sediment fill 

between the south end of the high ridges on the west flank of 

the Gorda Ridge and the MFZ continues eastward to the edge 

of Escanaba Trough (fig. 12A). Turbidity currents can enter 

Escanaba Trough only through a fairly narrow gap between the 

Gorda Ridge and MFZ (fig. 2), where the sill is currently at 

about 3,250-m water depth. Onlap of reflectors from the west 

indicates that this sill originally acted as a dam for currents 

moving from Tufts fan to the east along the MFZ (fig. 12A). 

Thus, the turbidite fill of Escanaba Trough is essentially flowstripped sediment from the thicker Cascadia-channel flows that 

reached the MFZ. North of the MFZ, pockets of low backscatter 

confirm ponding in the valleys between prominent ridges on the 

flank of the Gorda Ridge (figs. 10, 11A, B). The profile in figure 

11C crosses from the southern end of a prominent ridge southward to the base of the MFZ and shows there is no channel acting as a conduit for sediment flowing toward Escanaba Trough. 

The uppermost 50-100 m of sediment is flat-lying and smoothes 

underlying topographic relief along much of the crossing, 

except over a buried high in the middle of the profile. East of 

figure 11C, the buried ridge crops out, forming a bedrock island 

surrounded by sediment-smoothed sea floor (fig. 10). Figure 

10 also shows, north of this island, gently arcuate backscatter 

returns that might result from sediment waves formed as the 

turbidity currents flowed eastward around the island toward 

Escanaba Trough. These waveforms are subparallel to the probable flow direction and might be analogous with those common 

to sediment drifts (see review in Wynn and Stow, 2002). The 

ponded turbidite sequences along the MFZ and between ridges 

on the western flank of Gorda Ridge are part of the ponded 

basin-plain element for Tufts fan.

The upper 120 m of turbidites in Escanaba Trough that 

are the result of the glacial Lake Missoula floods formed 

from the largest flood events that have been recorded on 

land—those that produced turbidity currents thick enough 

to maintain flow across the ponded basin-plain element 

described above. Zuffa and others (2000) argued that the 

turbidite fill of Escanaba Trough could not have come from 

the east. Their argument was based on a study by Goldfinger 

and others(2000), who showed that the Astoria Channel, 

which extends from Astoria Canyon near the mouth of the 

Columbia River southward along the base of the continental 

slope, was blocked along the southern Oregon margin by the 

immense Heceta landslide about 110 ka. In addition, Wolf 

and others (1999) showed that the Astoria Channel south 

of the Heceta slide is filled with muddy sediment and has 

not been an active sediment-transport conduit. Using the 

thickness of sediment fill in Astoria Channel off northern 

California (approximately 15 m, Wolf and others, 1999), the 

evidence from the nearby Ocean Drilling Program (ODP) 

Site 1020 (Shipboard Scientific Party, 1997) shows that the 

channel probably has been inactive for more than 100 ka. 

An airgun profile across the mouth of Escanaba Trough 

(fig. 12A) shows that the turbidite fill of Escanaba Trough 

pinches out to the east on the southern end of one of the high 

mountains of Gorda Ridge. Available 3.5-kHz profiles also 

show that the latest Pleistocene sediment of Escanaba Trough 

onlaps and pinches out along the eastern margin of the 

trough (figs. 12B, C). Thus, the latest Pleistocene deposits 

in Escanaba Trough were deposited from the tops of southward-flowing turbidity currents that crossed Tufts fan, were 

deflected by the relief of the MFZ, and then flowed eastward 

until intercepted by the deep rift valley of Escanaba Trough.

Only a few sediment cores are known from the general 

area of Tufts fan. Core C4 (table 2 and fig. 2A) is from near 

the northeast corner of the fan in water depths of 3,180 m. 

It recovered nearly 3 m of late Pleistocene sediment with 

a terrigenous component (Duncan, 1968). In the lower fan 

area, core C6 (table 1 and fig. 2A) has a near-surface layer 

that dates to about 15.5 ka (if we correct the raw age from 

Dowsett and Poore, 1999, by making a reservoir correction 

for the mixture of benthic and planktic forams that they used 

for the carbon-14 age).

Adjacent to the lower fan, two cores recovered sediment 

with silty terrigenous components. At 3,136-m water depth, 

core C7 (table 1 and fig. 2A) recovered terrigenous silty clay; 

carbon-14 dates at depths of 5-6 cm and 12-13 cm in the core 

were 15.38 ka and 15.82 ka, respectively (Ortiz and others, 

1997). Farther west, core C8 (table 1 and fig. 2A) in 3,330-m 

water depth recovered sediment that was dated at 14.9 and 

15.0 ka at depths of 14-15 cm and 20-21 cm, respectively 

(Ortiz and others, 1997). These dated intervals overlie terrigenous sediment in the interval between depths of 172 and 257 

cm in the core.

These cores confirm that terrigenous sediment has been 

deposited on the western flank of Gorda Ridge (both within the 

fan area and to the west) between the lobe area of the fan and 

the thick, ponded sequence at the base of the MFZ. The age of 

the upper parts of these cores roughly coincides with the time of 

the Lake Missoula floods and other latest Pleistocene events in 

the northwestern United States and southwestern Canada.

Discussion

Age of Tufts Fan

There is no equivalent of an ODP sediment core that can 

be used to provide ground truth for estimating the age, periodicity of deposition, or character of sediment deposited on the Tufts 

fan. The available core data (table 2) support the conclusion that 

the last turbidites deposited on the fan are from the Lake Missoula floods. The deep erosion of Cascadia Channel into thick 

presumed turbidite deposits and the thicknesses of deposits 

(about 500 m) on the upper fan and in the area just north of the 

MFZ might indicate that turbidity currents have been active on 

the Pacific Plate during much of the Pleistocene.

The turbidity currents that were generated by glacial Lake 

Missoula and other latest Pleistocene flood events were able 

to reach the Escanaba Trough only because a pathway existed 
6 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

on the Pacific Plate as a result of previous, and fairly extensive, turbidite deposition. Creation of the Tufts fan involved 

substantially more sediment than the amount left by the latest 

Pleistocene flood pulses. Based on extrapolation of available 

age data on sediment from ODP Site 1037, it is unlikely that 

much, if any, of the sediment fill in Escanaba Trough can be 

older than 60 ka (using data from Brunner and others, 1999). 

The oldest date at Site 1037 is 32.2 ka at 317-m subbottom 

depth from a muddy interval that is underlain by about 185 

m of turbidite sand and mud. Using the slowest rate provided 

by Brunner and others (1999)—7.6 m/k.y. for the relatively 

muddy interval between 262.25 and 316.90 m subbottom—

gives an age of 56.5 ka for the basal turbidites. Sand beds 

are more common in the lower part of the hole, so the actual 

sedimentation rate would probably be greater. Thus, deposition of the turbidite section currently preserved in Escanaba 

Trough from flows moving across Tufts fan probably began 

only about 50 ka. It is possible that there are older turbidite 

deposits buried by volcanic flows and now uplifted as part of 

the terraces flanking the trough axis. Tilted and deformed sediment is common on the western side of the Escanaba Trough 

(fig. 12A), suggesting that active tectonism and uplift might 

have prevented earlier flows from reaching the axis from Tufts 

fan. Normark and Reid (in press) estimated that deposits on 

Tufts fan equivalent in age to the Lake Missoula deposits in 

Escanaba Trough account for less than 10 percent of the total 

volume of turbidites in the fan. Thus, as a minimum, the fan 

may have been forming throughout the late Pleistocene. 

Tufts fan could have begun to form shortly after Cascadia Channel established the connection with the Pacific Plate 

through the BFZ. An upper limit on the age of the fan might 

be given by the time that Pleistocene catastrophic floods in 

the Pacific Northwest began. McDonald and Busacca (1988) 

reported evidence for flood-cut unconformities in loess in 

the Channeled Scabland; the youngest pre-Wisconsin flood 

episode was about 36 ka. These authors further suggest that 

this event was one of at least five episodes of flooding in the 

scabland before the Lake Missoula jökulhlaups. The earliest 

of these episodes might be as old as 790 ka (McDonald and 

Busacca, 1988). Recent work has suggested that cataclysmic 

flooding in the Pacific Northwest might have been common 

throughout much or all of the Pleistocene, beginning between 

2.5 and 1.5 Ma (Bjornstad and others, 2001; Pluhar and others, 

2002). The Heceta submarine slide (about 110 ka) blocked 

the Astoria Channel along the base of the continental slope, 

effectively blocking an eastern pathway to Escanaba Trough 

and the Pacific Plate (Goldfinger and others, 2000; Wolf and 

others, 1999). The Heceta slide, however, is only the youngest 

of three catastrophic failures of similar size recognized along 

the Oregon continental margin. Goldfinger and others (2000) 

estimate that the Coos Basin slide, which is immediately south 

of the Heceta slide, occurred about 460 ka; this slide deposit 

would also have acted to deflect southward-directed sediment 

transport to the west through the Blanco Fracture Zone. An 

even older large-scale failure, the Blanco slide, occurred 1.2 Ma 

(Goldfinger and others, 2000). Thus, it is probable that turbidite sediment has been moving through the Blanco Fracture 

Zone throughout the late Pleistocene, and the initial deposition 

on the Tufts fan may record the beginning of such turbidite 

deposition on the Pacific Plate.

Tufts Fan Elements and Tufts Abyssal Plain

The Tufts fan is more than 350 km in length between the 

Cascadia Channel and the MFZ and is generally 60-70 km 

wide in the upper and middle fan areas and narrows to about 

40 km in the south; it has a total area of about 23,600 km2 

(fig. 13). The airgun seismic-reflection profiles show thick 

sections of sediment with the acoustic character of classic turbidite deposits over the eastern part of the study area (figs. 2A, 

13). The growth of the fan, however, did not result in a prominent feeding channel or distributary system such as found on 

most modern turbidite fans. This, in part, probably results from 

the confinement of the turbidity currents to the valleys between 

the numerous elongate ridges on the western flank of Gorda 

Ridge. Where turbidity currents cannot spread laterally (and 

form a fan-shaped deposit) because of confinement to a narrow 

basin, the walls of the basin act as channel margins, keeping 

the flow thick enough to keep moving (see fig. 9 in Normark 

and Piper, 1991). The upper-fan and channeled-lobe areas of 

Tufts fan are thick enough to have buried many of the hills on 

the flank of Gorda Ridge. Farther south, there is sufficient relief 

of the elongate ridges to keep the turbidity currents confined 

as they flow south toward the MFZ. The result is that the Tufts 

fan has poorly defined channel and lobe features on the middle 

fan element but has extensive lower fan and basin elements that 

show little surface relief because of ponding (fig. 13).

The Tufts fan is a very small (in area) turbidite deposit 

compared to the Tufts Abyssal Plain (see fig. 12 in Normark and Reid, in press). The relief of the Cascadia Channel 

throughout the area of overbank flow, which is the source of 

the Tufts fan, is 150-200 m. The deposits of Tufts fan represent 

only the uppermost, flow-stripped portions of the tremendous 

turbidity currents that flowed through the BFZ. Significant 

volumes of the flows confined within the Cascadia Channel 

likely continued westward some 1,500 km or more (Hurley, 

1964; Normark and Reid, in press) towards the end of the 

channel within Tufts Abyssal Plain (fig. 1). Accordingly, 

substantially more sediment was probably deposited on the 

abyssal plain than in the Tufts fan. Volumetric calculations of 

the amounts of terrigenous sediment on the Pacific Plate suggest that the total volume of Tufts fan turbidite deposits is less 

than 10 percent of that on the Tufts Abyssal Plain (Normark 

and Reid, in press).

Conclusions

The Tufts submarine fan formed as a result of late Pleistocene, and perhaps earlier, deposition from turbidity currents that 

were able to cross to the west of the Gorda Ridge spreading axis 
References 7

through the Blanco Fracture Zone and deposit on the Pacific 

Plate. Catastrophic floods from glacial Lake Missoula and 

earlier late Pleistocene outbursts carried enormous amounts of 

sediment from the Pacific Northwest to the ocean. These floods 

continued to transport sediment downslope as hyperpycnally 

generated turbidity currents following the Cascadia Channel to 

the Pacific Plate, eventually building the 350-km-long Tufts fan 

as a result of both flow stripping and normal overbank loss of 

sediment from Cascadia Channel. The Tufts fan buried ridgeand-valley topography on the western flank of Gorda Ridge and 

eventually became a sedimented pathway to the Mendocino 

Fracture Zone and Escanaba Trough. By the latest Pleistocene, 

that is, after about 60 ka, Tufts fan had sufficiently aggraded to 

allow the largest of the glacial lake outbursts to reach Escanaba 

Trough, where the flows were trapped and have provided a welldocumented record of some of these flood events at ODP Site 

1037 (Zuffa and others, 2000). 

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8 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

on the Pacific Plate from late Pleistocene North-American 

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United States: Journal of Geology, v. 108, p. 253-274.
Figures 9

Table 1. Key turbidite beds in Escanaba 

Trough and water depth (top of flow) at the 

time of deposition of each bed (adapted from 

Normark and Reid, in press).

Table 2. Locations of cores with evidence for glacial Lake Missoula deposits (adapted from Normark and Reid, in press).

Bed Water depth to top of 

turbidity current (m)

H 3,126

D 3,136

G 3,144

F 3,165

B 3,173

E 3,188

C 3,194

Label on 

(fig. 2A)

Original core numberWater

depth (m)

Depth in core 

(m) Age (ka) Reference

C1 6509-21A 3,232 2.3

5.8

15.9

27.2

Duncan and others, 1970

C2 6509-25A 3,334 2.55-2.9 9.67 Duncan and others, 1970

C3 6604-1 3,329 gravel late Pleistocene Griggs and others, 1970

C4 6604-3 3,180 3 meters total late Pleistocene Duncan, 1968

C5 6609-13 3,266 1.8-2.25 13.15 Duncan and others, 1970

C6 W8809A-29GC 3,288 (near surface) 15.5 Dowsett and Poore, 1999

C7 W8809A-31GC 3,136 0.05-0.06

0.12-0.13

15.38

15.82

Ortiz and others, 1997

C8 W8809A-57GC 3,330 0.14-0.15

0.20-0.21

14.9

15.0

Ortiz and others, 1997
10 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

Figure 1 is a map encompassing the area between about 40° and 47° north latitude and from the coastline of Washington, 

Oregon, and northern California out to 132.4° west longitude. Features shown include Juan de Fuca and Gorda Ridges, Blanco 

and Mendocino Fracture Zones, Astoria Fan at the base of the slope to the west and south of the Columbia River mouth, Heceta 

Slide at the base of the slope at about 43.8° north latitude, Cascadia Channel, which heads off the Columbia River mouth and 

extends west and south, through Blanco Fracture Zone, continuing westward to the Tufts Abyssal Plain, Escanaba Trough at 

the southernmost end of the Gorda Ridge, and the subject of this study, Tufts fan west of Gorda Ridge, between Blanco Fracture 

Zone and Mendocino Fracture Zone. A rectangle in the middle of the figure denotes the location of Figure 2. An expanded map of 

Escanaba Trough gives the locations of Ocean Drilling Program Site 1037, Deep Sea Drilling Program Site 35, and the high-resolution seismic profile shown in figure 3. Caption follows.

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Figure 1. Schematic map showing path of late Pleistocene glacial flood sediment from the Columbia River mouth to the 

Tufts fan, Escanaba Trough, and Tufts Abyssal Plain (Normark and Reid, in press). Rectangle with thick lines shows location 

of figure 2; enlargement gives the location of Deep Sea Drilling Program (DSDP) and Ocean Drilling Program (ODP) drill sites 

and the high-resolution 4.5 kHz profile (fig. 3).
Figures 11

Figure 2 includes a map (A) encompassing the study area, between about 40° and 45° north latitude and 126° and 131° west longitude, 

and (B) GLORIA side-scan sonar backscatter imagery of the central part of this area. On the map, the west-northwest trending Blanco 

Fracture Zone connects the Juan de Fuca Ridge at the upper left corner to the Gorda Ridge along the right margin. The Mendocino Fracture Zone extends along the southern limit of the figure. Cutting through Blanco Fracture Zone is Cascadia Channel. Tufts fan extends 

southward from Cascadia Channel where it crosses Blanco Fracture Zone, down to Mendocino Fracture Zone, where it curls eastward 

around the south end of Gorda Ridge to Escanaba Trough. Core locations are as follows: core C1 in a trough within the western Blanco 

Fracture Zone, cores C2 and C3 along its margin south of Blanco Fracture Zone, core C4 just to the south of the middle portion of Blanco 

Fracture Zone, core C5 in an isolated basin within Gorda Ridge, core C6 within the southern half of Tufts fan, and cores C7 and C8 west 

of the Tufts fan margin in the lower left quarter of the figure. Caption follows.

Figure 2. Map and acoustic backscatter mosaic of the study area. A, Map shows physiographic features and data used in 

this study. In addition, the locations of GLORIA imagery used in figures 2B, 9, and 10 are noted by black rectangles. Locations of 

seismic-reflection profiles in figures 4 and 12, and core locations (table 2) are also shown. B, GLORIA sidescan-sonar backscatter imagery (full resolution of data used in EEZ-SCAN Scientific Staff, 1986) showing location of figures 5-8.

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12 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

Figure 2 includes a map (A) encompassing the study area, between about 40° and 45° north latitude and 126° and 131° west longitude, 

and (B) GLORIA side-scan sonar backscatter imagery of the central part of this area. On the map, the west-northwest trending Blanco 

Fracture Zone connects the Juan de Fuca Ridge at the upper left corner to the Gorda Ridge along the right margin. The Mendocino Fracture Zone extends along the southern limit of the figure. Cutting through Blanco Fracture Zone is Cascadia Channel. Tufts fan extends 

southward from Cascadia Channel where it crosses Blanco Fracture Zone, down to Mendocino Fracture Zone, where it curls eastward 

around the south end of Gorda Ridge to Escanaba Trough. Core locations are as follows: core C1 in a trough within the western Blanco 

Fracture Zone, cores C2 and C3 along its margin south of Blanco Fracture Zone, core C4 just to the south of the middle portion of Blanco 

Fracture Zone, core C5 in an isolated basin within Gorda Ridge, core C6 within the southern half of Tufts fan, and cores C7 and C8 west 

of the Tufts fan margin in the lower left quarter of the figure. Caption follows.

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Figure 2. Continued. Map and acoustic backscatter mosaic of the study area. A, Map shows physiographic features and 

data used in this study. In addition, the locations of GLORIA imagery used in figures 2B, 9, and 10 are noted by black rectangles. 

Locations of seismic-reflection profiles in Figures 4 and 12, and core locations (table 2) are also shown. B, GLORIA sidescansonar backscatter imagery (full resolution of data used in EEZ-SCAN Scientific Staff, 1986) showing location of figures 5-8.
Figures 13

Figure 3 contains a schematic sediment section of ODP site 1037B, to about 85 meters subbottom depth, and a high-resolution 

deep-tow 4.5 kHz profile trending northeast–southwest near the ODP site. The sediment section contains prominent silty-sand 

layers that generally become thinner upsection and are separated by thin mud intervals. Nine of these sandy and silty parts 

of the core are correlated with hard returns within the high-resolution profile. Radiocarbon age dates included are 15,750 ± 70 

years at about 56 m subbottom, 10,882 ± 85 years at about 25 m, and 8,762 ± 95 years at about 2 m. Caption follows.

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Figure 3. Deep-tow 4.5-kHz high-resolution reflection profile showing the characteristic spacing of the 

turbidite reflector sequence (A to I) in Escanaba Trough at ODP Hole 1037B; the correlation with the sediment 

log is given (modified from Zuffa and others, 2000). Locations of ODP Hole 1037B and 4.5-kHz profile are shown 

in figure 1 (enlarged map).
14 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

Figure 4 contains four seismic-reflection profiles crossing Cascadia Channel, showing progressive change of the channel from a deep 

“V” shape in the middle of a thick packet of probable turbiditic sediment, to a broader, flat-bottomed channel, and finally back to a deep, 

open ‘V’ shape at the eastern edge of the Tufts Abyssal Plain. Included on the three down-channel profiles are two horizontal bands in 

the water column that represent the range of the uppermost parts of the latest-Pleistocene turbidity currents that made it to Escanaba 

Trough. Caption follows.

Figure 4. Single-channel, airgun seismic-reflection profiles crossing Cascadia Channel. The profiles are oriented such that the view is 

down the channel axis to emphasize that the right-hand overbank area is shallower than the left margin on all profiles. Profile locations noted in figure 2A. A, Profile on the Juan de Fuca Plate. B, Profile just north of the exit point in the Blanco Fracture Zone. C, Profile 

immediately south of the Blanco Fracture Zone near the apex of the Tufts fan. D, Profile from the easternmost part of Tufts Abyssal Plain. 

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Figures 15

Figure 5 contains three acoustic profiles of the upper Tufts fan, south of Cascadia Channel, with two horizontal bands that represent the 

range of the tops of the turbidite flows that made it to Escanaba Trough. Caption follows.

Figure 5. Seismic-reflection profiles across the upper Tufts fan. Locations of profiles are noted on figure 2B. A, Single-channel airgun 

profile near the point of overflow of turbidity currents from Cascadia Channel, showing a generally convex upward cross section without a distinct channel. B, Single-channel airgun profile farther south crossing the broad, shallow, leveed Tufts fan channel. C, Highresolution 3.5-kHz profile highlights Tufts fan channel and adjacent right-hand levee (facing down channel axis) with sediment waves.

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16 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

Figure 6 contains four seismic-reflection profiles from areas near Cascadia Channel. Included on the profiles are two horizontal bands in 

the water column that represent the range of the uppermost parts of the latest-Pleistocene turbidity currents that made it to Escanaba 

Trough. Caption follows.

Figure 6. Seismic-reflection profiles in overflow areas adjacent to the Cascadia Channel and upper Tufts fan, showing extensive 

ponding of sediment from turbidity currents. Profile locations are noted in figure 2B. A, Single-channel airgun seismic-reflection profile 

crossing thick, flat-lying deposits ponded in a trough within the southern margin of Blanco Fracture Zone (BFZ), west of Cascadia Channel. B, High-resolution 3.5-kHz profile, showing a growth fold within the trough. C, Single-channel airgun reflection profile, showing 

thick, flat-lying deposits east of Cascadia Channel, south of BFZ. D, High-resolution 3.5-kHz profile of the eastern part of the profile in 

C, demonstrating that the most recent deposits have smoothed any underlying relief. The acoustic character of the upper part of this 

sediment fill mimics that seen in Escanaba Trough (figure 3). 

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Figures 17

Figure 7 contains four seismic-reflection profiles across the middle and lower fan elements of Tufts fan. Included on the profiles are 

two horizontal bands in the water column that represent the range of the uppermost parts of the latest-Pleistocene turbidity currents 

that made it to Escanaba Trough. Caption follows.

Figure 7. Seismic-reflection profiles across the middle and lower fan areas of Tufts fan. Profile locations in figure 2B. See figure 6 for 

explanations of yellow/green colors and arrows. A, B, Single-channel airgun seismic-reflection profile (A) and high-resolution 3.5-kHz 

profile (B) cross the middle fan area, showing small channels and scour depressions. C, Single-channel airgun seismic-reflection profile, showing ponded turbidites on the lower fan as well as flow-stripped deposits trapped between ridges on the flank of Gorda Ridge. 

The crest of the ridge, marked ‘R’, is near 3,100-m water depth; even the thickest flows that reached Escanaba Trough could not overtop 

the ridge at the location of this profile. D, High-resolution 3.5-kHz profile across the ponded lower fan. 

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18 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

Figure 8 contains three high-resolution 3.5-kHz profiles across bathymetrically isolated areas adjacent to and east of Tufts fan. Profile A illustrates the difference between the closely spaced, rhythmically bedded lower Tufts fan deposits and, in an isolated pocket 70 m deeper to the 

east, much thicker beds, similar in character to Escanaba Trough turbidites. Caption follows.

Figure 8. High-resolution 3.5-kHz reflection profiles with evidence of flow stripping adjacent to the Tufts fan. Profile locations in figure 

2B. A, This profile from the lower Tufts fan shows the typical character of sandy turbidites on the fan (left segment of profile) and an 

acoustic character similar to that found in Escanaba Trough in an isolated pocket (east end of profile; see text for details). B, C, Profiles 

showing ponded turbidites with a character similar to that of the Escanaba Trough fill (see fig. 3). The flat-lying deposits resulted from 

thicker, presumably flow-stripped turbidity currents reaching these isolated basins. 

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Figures 19

Figure 9 is GLORIA side-scan sonar backscatter imagery between about 42° and 44.2° north latitude and 127.5° and 130° west longitude and covers the same area as figure 2B. This figure illustrates the locations of the fan elements and associated areas of turbidite 

deposition. Caption follows.

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Figure 9. GLORIA sidescan-sonar backscatter image of the upper, middle, and lower Tufts fan and of the 

Tufts fan channel (dark red; see also fig. 5). Image location is the same as figure 2B and is shown in figure 2A. 

Outlined areas north of Cascadia Channel are the northern overbank deposits between abyssal hills (within 

brown line) and flow-stripped deposits within troughs of the Blanco Fracture Zone (within thick blue line; see 

fig. 6A, B). The dark orange polygon encompasses the upper fan and adjacent overbank deposits (figs. 5 and 

6C, D). Light orange line encompasses the middle fan with small channels and scours around abyssal hills (fig. 

7A, B). Yellow delineates the northeast corner of the lower fan (fig. 7C, D). Turbidity-current deposits that were 

trapped in small basins show as very low amplitude backscatter (black shading) along the eastern margin of 

the Tufts fan (see along longitude 128°30’ W) and are outlined in thin blue lines (see also fig. 8).
20 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

Figure 10 is GLORIA side-scan sonar backscatter imagery between about 41.1° and 40.2° north latitude and 129.1° and 127.4° west longitude. 

Caption follows.

Figure 10. GLORIA sidescan-sonar backscatter image of the sea floor immediately north of the Mendocino Fracture Zone along the 

pathway of turbidity currents that flowed into Escanaba Trough. Image location noted in figure 2A. Much of the sediment-smoothed 

area (darker gray to black shading) is underlain by several hundred meters of ponded turbidite sediment (fig. 11). Locally, the ponded sediment (outlined in thin dashed blue line) shows as very low amplitude (black) backscatter in areas between the ridges of the 

southern terminus of Gorda Ridge (see fig. 11B). Much of the area within Escanaba Trough is also low backscatter (also outlined in thin 

dashed blue), which is consistent with the ponding of the turbidity currents after being trapped in the spreading-center axis. Orange 

dashed lines show direction of possible flow paths; red dashed lines show possible directions of flow stripping over low hills within 

the western Gorda Ridge flank. Solid yellow circles indicate locations of ODP and DSDP core sites. Location of seismic-reflection and 

3.5-kHz profiles of figures 11 and 12A are shown. 

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Figures 21

Figure 11 contains three single-channel airgun profiles north of Mendocino Fracture Zone. Included on the profiles are two horizontal bands in 

the water column that represent the range of the uppermost parts of the latest-Pleistocene turbidity currents that made it to Escanaba Trough. 

Caption follows.

Figure 11. Single-channel, airgun seismic-reflection profiles showing extensive ponding of sediment from turbidity currents in the area 

north of Mendocino Fracture Zone (MFZ). Image locations noted in figure 10. A, North-south profile showing the smoothed sea floor and 

deep packet of ponded sediments. B, East-west profile that crosses the ridges on the west flank of Gorda Ridge, showing ponding in the 

valleys. C, Airgun profile showing the extensive ponding and lack of a well-defined channel leading to Escanaba Trough, north of the 

Mendocino Fracture Zone. 

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22 Tufts Submarine Fan: Turbidity-Current Gateway to Escanaba Trough 

Figure 12 contains three seismic-reflection profiles across the mouth of Escanaba Trough, north of Mendocino Fracture Zone. Included on 

the profiles are two horizontal bands in the water column that represent the range of the uppermost parts of the latest-Pleistocene turbidity 

currents that made it to Escanaba Trough. Caption follows.

Figure 12. Seismic-reflection profiles across the southern end of Escanaba Trough (parallel to the Mendocino Fracture Zone) showing 

the eastward onlap of the turbidite deposits that are contiguous with Escanaba Trough fill. Image locations noted in fig. 2A. See figure 11 

for explanation of yellow/green colors and arrows. A, Airgun seismic-reflection profile. B, C, 3.5-kHz high-resolution profiles. 

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Figures 23

Figure 13 is a map encompassing the same area as figure 2A and showing Tufts fan in relation to Juan de Fuca and Gorda Ridges, Blanco 

and Mendocino Fracture Zones, and Cascadia Channel. It illustrates the geographical extent of the Tufts fan, with fan elements differentiated (upper fan, middle fan, and lower fan and basin plain combined). Arrows suggest paths for turbidity-current flows to Escanaba 

Trough and possible flow directions for sediment stripped off the currents moving from Tufts fan to the isolated basins to the east. Caption 

follows.

Figure 13. Acoustic-facies interpretation of the Tufts fan and areas with flow-stripped and trapped turbidite sediment. Outside of the 

GLORIA map area (see fig. 2), the western limit of Tufts fan is poorly constrained but is assumed to be formed by north-south-trending 

ridges on the flank of Gorda Ridge similar to the fan boundary north of 43° N latitude. Available data suggest that the flow pathway(s) 

from Tufts fan to Escanaba Trough are now marked by areas with thick ponded deposits and, as such, are probably part of the basinplain element for this system. See text for details. Area shown is same as for figure 2.

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