Cascadia Channel Research Articles

Extensive Deposits on the Pacific Plate from Late Pleistocene North American Glacial Lake Outbursts

Abstract One of the major unresolved issues of the Late Pleistocene catastrophic‐flood events in the northwestern United States (e.g., from glacial Lake Missoula) has been what happened when the flood discharge reached the ocean. This study compiles available 3.5‐kHz high‐resolution and airgun seismic reflection data, long‐range sidescan sonar images, and sediment core data to define the distribution of flood sediment in deepwater areas of the Pacific Ocean. Upon reaching the ocean at the mouth of the Columbia River near the present‐day upper continental slope, sediment from the catastrophic floods continued flowing downslope as hyperpycnally generated turbidity currents. The turbidity currents resulting from the Lake Missoula and other latest Pleistocene floods followed the Cascadia Channel into and through the Blanco Fracture Zone and then flowed west to the Tufts Abyssal Plain. A small part of the flood sediment, which was stripped off the main flow at a bend in the Cascadia Channel at its exit point f...

Paleoseismicity of the Cascadia Subduction Zone: Evidence from turbidites off the Oregon‐Washington Margin

Cores from Cascadia deep‐sea channel contain sequences of turbidites that can be correlated and dated by the first occurrence of volcanic glass from the Mount Mazama eruption (6845±50 radiocarbon yrBP). Turbidity currents from the tributaries appear to have occurred synchronously to form single deposits in the main channel, there being only 13 turbidite deposits in the lower main channel since the Mazama eruption, instead of the twice as many expected if the tributaries had behaved independently. In addition to the Cascadia Channel, 13 post‐Mazama turbidites have been deposited in the Astoria Canyon and at two sites off Cape Blanco, sample locations that span 580 km of the Oregon‐Washington margin. Pelagic intervals deposited between the turbidites suggest that in each place the turbidity currents occurred fairly regularly, every 590±170 years on average. The best explanation of the spatial and temporal extent of the data is that the turbidity currents were triggered by 13 great earthquakes on the Cascadia subduction zone. The variability of turbidite timing is similar to that for great earthquake cycles. The thickness of the topmost pelagic layer suggests the last event was 300±60 years ago (from three places along the margin), but this number may be a biased underestimate. It is, however, consistent with the youngest sudden‐subsidence event on the Washington coast. The turbidite data demonstrate that the near‐term hazard of a great earthquake on the Cascadia subduction zone is of the order of 2–10% in the next 50 years.

Lateral migration of Cascadia Channel in response to accretionary tectonics

Research Article| February 01, 1989 Lateral migration of Cascadia Channel in response to accretionary tectonics H. A. Karl; H. A. Karl 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar M. A. Hampton; M. A. Hampton 1U.S. Geological Survey, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar N. H. Kenyon N. H. Kenyon 2Institute of Oceanographic Sciences, Wormley, Surrey GU8 5UB, England Search for other works by this author on: GSW Google Scholar Author and Article Information H. A. Karl 1U.S. Geological Survey, Menlo Park, California 94025 M. A. Hampton 1U.S. Geological Survey, Menlo Park, California 94025 N. H. Kenyon 2Institute of Oceanographic Sciences, Wormley, Surrey GU8 5UB, England Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1989) 17 (2): 144–147. https://doi.org/10.1130/0091-7613(1989)017<0144:LMOCCI>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation H. A. Karl, M. A. Hampton, N. H. Kenyon; Lateral migration of Cascadia Channel in response to accretionary tectonics. Geology 1989;; 17 (2): 144–147. doi: https://doi.org/10.1130/0091-7613(1989)017<0144:LMOCCI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract In response to the progradation of the Washington continental slope and uplift of sediment at the eastern edge of Cascadia Basin, Cascadia Channel has altered its course by migrating seaward where the channel leaves the base of the slope and passes through the swale between Nitinat and Astoria submarine fans. Long-range side-scan sonar and acousticreflection data reveal a series of descending terraces, averaging 3 km in width and 10 m in height, between the base of the slope and Cascadia Channel that evince the lateral migration of the channel. Cascadia Channel, in this specific case, has responded as a terrestrial fluvial system does to tectonic tilt. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The nature and evolution of deep‐sea channel systems

Abstract A distinction is drawn between sea‐floor canyons, which are incised into bedrock, and fan valleys and deep‐sea channels, which are cut in unconsolidated sediment. The formation of continental margin canyons/fans and deep‐sea channels is an inevitable consequence of continental margin rifting and sea‐floor subsidence. Such submarine sediment transport systems are amongst the longest‐lived physiographic features on earth, with the Bounty Channel system being more than 50 Myr old. Many deep‐sea channels form the distal part of ocean‐margin sediment transport systems, being incised 100–350 m into ocean‐floor sediments, traversing great distances over the ocean‐basin floor, and generally terminating on an abyssal plain. The course of each deep‐sea channel is, however, unique. Channel locations are controlled primarily by inherited basement relief, and, during their evolution, by rates and patterns of lithospheric subsidence and sedimentation. In the early stages of ocean‐basin formation, deep‐sea channels may issue from the axial parts of marginal rifts, or directly from slope canyon‐fan systems. As an ocean basin widens, margin‐connected channels may become trapped within the strip of oldest (and therefore deepest) oceanic crust at the continent/ocean interface, and will therefore be margin‐parallel features. In some cases, as for the Cascadia Channel, channels may escape from the ocean‐margin deep, bypassing the spreading ridge via a fracture zone. Deep‐sea channels and their associated sediments are influenced also by global sea‐level change, by rate of turbidity current generation from the headward continental margin, by rates of pelagic sediment supply, by differential levee development consequent upon the Coriolis effect, and by the operation of deep‐sea current systems with their associated sediment drifts. The survival of deep‐sea channels as long‐lived features necessitates that rates of long‐term subsidence at the channel terminus exceed sediment accumulation.

A locally formed deep ocean canyon system along the Blanco Transform, Northeast Pacific

A dissected terrain resembling a shelf-edge canyon system with individual canyons up to 100 m in relief, 3 km in width, and 10 km in length is found along the south flank of the Cascadia Channel within the central Blanco Transform zone. The channels apparently formed from a combination of downcutting from turbidity currents off the Blanco Ridge and from backcutting due to mass-wasting. The relationships between the transform tectonics and the formation of the canyon are presented in a model which proposes both a direct link via triggering of slides from earthquakes and an indirect link associated with lowering the local base level of Cascadia Channel, thalweg downcutting, and wall-steepening leading to increased mass-wasting.

Geomorphic Features of Oregon-Washington Project EEZ-SCAN: ABSTRACT

During Leg 4 of Project EEZ-SCAN, long-range side-scan sonographs and seismic-reflection profiles were collected off Oregon and Washington, from the edge of the continental shelf to the boundary of the United States Exclusive Economic Zone (375 km from shore). The survey was extended seaward where necessary to include the Juan de Fuca Ridge. The project utilized the British GLORIA side-scan sonar system. The records were slant-range corrected and anamorphosed, and mosaics were constructed at a scale of 1:375,000. The sonographs display precise geometry of the major geomorphic features of the area: accretionary ridges, submarine canyons, and fan valleys on the continental slope; deep-sea fans and channels in Cascadia basin; and elongate volcanic ridges making up Gorda and Juan de Fuca Ridges. Canyons with gullied walls deeply incise the upper continental slope off Washington. On the lower slope, the regime apparently changes from one of downcutting to one of overbank deposition. Cascadia basin and Cascadia Channel record intricate and complex drainage histories. The channel is not evident as a major feature on Nitinat Fan but becomes more prominent to the south, especially where it crosses Blanco Fracture Zone and enters Tufts Abyssal Plain. Recent tectonic deformation of oceanic crust in the vicinity of Gorda Ridge is evident in the sonographs. For example, long, linear volcanic ridges flanking the spreading center are distorted and rotated westward at the north end where the Gorda Ridge meets the Blanco Fracture Zone. End_of_Article - Last_Page 262------------

Distribution and diversity of holothuroids (Echinodermata) on Cascadia Basin and Tufts Abyssal Plain

The pattern of diversity, species composition, and inter-sample similarity of the holothuroid fauna was examined for 95 beam trawl samples from below 2000 m on the Cascadia Basin and Tufts Abyssal Plain off Oregon, U.S.A. Abundance as inferred from catch size, diversity, species composition, and zonation all showed major change over the sampled area where there was a depth change. Where depth remained relatively constant across the floor of Cascadia Basin, faunal changes were minor in spite of progressive isolation from land. Overall bathymetric patterns of zonation and diversity were basically like those found for other faunal groups in the deep-sea depth. The distribution of minor species indicated that the holothuroid fauna at the base of the continental slope, the apron of Astoria Fan, and near Cascadia Channel might be slightly different from that at similar depths elsewhere in the sampled area. The marked uniformity of the holothuroid fauna across the basin floor appeared to be restricted to epifaunal sediment-feeding species. Infaunal forms were more abundant at the slope base, similar to previous findings for the macro-infauna.

Comparison of the bottom nepheloid layer and late Holocene deposition on Nitinat Fan: Implications for lutite dispersal and deposition

A study of 56 sediment cores and 121 nephelometer profiles from Nitinat deep-sea fan shows variations in late Holocene accumulation rates and sediment texture which parallel variations in thickness and suspended sediment load of the bottom nepheloid layer. Furthermore, accumulation rates, sediment texture, and nepheloid layer variables all show a substantial degree of correlation with fan topography. In general, the nepheloid layer thickens (>100 m) and suspended sediment loads increase (>100 µg/cm 2 ) above Cascadia Channel (the major channel crossing the fan) as well as above the northern flank of the fan. Over levees and the western portion of the fan, the nepheloid layer thins to 2 . Cascadia Channel and the northern flank of the fan have been loci of rapid sedimentation, with accumulation rates ranging from approximately 5 to greater than 12 mg/cm 2 /yr. In contrast, the apex and western reaches of the fan have significantly lower accumulation rates: 1 to 5 mg/cm 2 /yr. Detailed size analysis of bottom sediments shows that areas characterized by rapid sedimentation and a thick, heavily loaded nepheloid layer have more medium to fine silt (5 to 7 ϕ) than the clay-rich (>8 ϕ) sediments from interchannel areas with low accumulation rates and a thin, lightly loaded nepheloid layer. The data suggest that turbid water moves continuously down Cascadia Channel and the northern flank. The transport mechanism is size-selective and topographically controlled, concentrating silt-sized detritus in topographic lows. The data also suggest a positive downward flux of sediment particles within the nepheloid layer, at least when averaged over a significant period of time.

Origin and development of Cascadia deep-sea channel

Cascadia channel formed initially in the north-south oriented topography on the eastern flank of the actively spreading Juan de Fuca ridge. The late Cenozoic volcanic basement was first covered by transparent pelagic and hemipelagic sediments, which were then overlain by horizontally deposited turbidites. Throughout much of its early history Cascadia channel probably existed only as a low-relief leveed transportational-depositional feature. With the onset of late Pleistocene glaciation and the related lowering of sea level, large volumes of sand and gravel from the continent deposited on the upper slope or the outer shelf led to the initiation of erosive turbidity currents, which converted the lower and middle portions of Cascadia channel into an erosional feature. This activity, combined with a change in base level and/or channel gradient, led to the initiation of downcutting. During this period of channel erosion the plain on either side of the channel was apparently being built up by turbidity current flows proceeding southward along the western part of Cascadia abyssal plain and west from Astoria fan. During Holocene time, turbidity currents derived from Columbia River sediments continued to flow the length of Cascadia channel and through the Blanco fracture zone. Within the past 6600 years a downdropped basin in the fracture zone has been ponding the Holocene flows. The upper channel remains a depositional feature, and turbidity currents continue to overflow the channel onto levees. Along portions of the middle channel, perhaps owing to increased gradients and backcutting, the flows remain entirely channelized and are either erosional or nondepositional. Along the deeply incised lower channel, Holocene flows have deposited thick layers of sediment on the channel floor, and no overflow has occurred.

Continuity of Turbidity Current Flow and Systematic Variations in Deep-Sea Channel Morphology

When a turbidity current flow decreases in velocity due to a decrease in bottom slope, the thickness of the flow must correspondingly increase to maintain continuity of discharge. This increase has been offered as a possible explanation for observed systematic increases in the relief of submarine channels along their lengths. A simplified computer model of turbidity current flow along a channel is developed which indicates that without any dilution of the flow by water entrainment, a reasonable decrease in channel-axis slope could more than double the thickness of the flow. With dilution, the thickness could easily increase by a factor four or more. The systematic increases in channel relief might therefore be explained. The approach is applied to Cascadia Channel, located off the coast of the northwest United States, to test whether reasonable amounts of flow dilution could account for the observed increase in channel relief. It is found that continuity of flow could explain much of the increase, but subsequent channel erosion (deepening and widening) has to be called upon to account for the entire increase in channel cross-sectional area.

Heat flow through the floor of Cascadia Basin

Forty-one measurements of heat flow, including three close-spaced groups of measurements, were taken at positions extending from the continental slope off Oregon to the east flank of the Juan de Fuca ridge. Individual values ranged from 1.08 μcal/cm2 sec in 445 meters of water on the continental slope off Oregon to 7.21 μcal/cm2 sec measured in 2740 meters of water near the Juan de Fuca ridge crest. The mean of the 41 heat-flow values is 2.86 μcal/cm2 sec, which is considerably higher than the approximate global mean of 1.5 μcal/cm2 sec. This high average heat flow fits the previously deduced world heat-flow pattern, which includes a high over the eastern Pacific. The distribution of 16 heat-flow measurements taken from near the base of the continental slope off Oregon westward to Cascadia channel has a broad peak between 1.50 and 2.99 μcal/cm2 sec. The distribution of 15 heat-flow measurements taken from west of Cascadia channel to near the Juan de Fuca ridge crest has a relatively sharp peak between 3.50 and 3.99 μcal/cm2 sec. The results of this research, combined with existing heat-flow data for the west flank of the Juan de Fuca ridge, show that the heat-flow profile across this ridge is not symmetrical. Unusually low values predominate on the west-flank, whereas above average values dominate the east flank of the Juan de Fuca ridge.

Deep-Sea Gravel from Cascadia Channel

Layers of coarse Pleistocene gravel have been cored in the Cascadia Deep-Sea Channel up to 750 km along its course. Petrographic study indicates that the pebbles are lithologically similar to a number of rock types exposed along the Columbia River and its tributaries in Oregon and eastern Washington. The catastrophic late Pleistocene glacial floods which scoured this area of the Pacific Northwest transported coarse material derived from these outcrops down the river to the ocean. These catastrophic events are believed to have generated high-velocity and high-density turbidity currents which transported the coarse sediment for many hundreds of kilometers along the sea floor.

Mineralogy, provenance, and dispersal history of late Quaternary deep-sea sands in Cascadia Basin and Blanco fracture zone off Oregon

Abstract The mineralogy of sandy sediments deposited during the late Pleistocene and Holocene in southern Cascadia Basin and the adjoining Blanco Fracture Zone displays systematic regional and temporal trends. The light-mineral constituents of these sands are lithic, arkosic, or volcanic in composition. They are mainly derived from extrusive and intrusive basic igneous rocks. Four deep-sea heavy-mineral provinces (A, B, C, and D) are distinguishable in the area investigated. Province A lies in the Blanco Fracture Zone--Gorda Ridge transition area. Textural and mineralogical compositions of these deposits suggest local submarine volcanism. The volcanism may be associated with sea-floor spreading along the young crestal zone of Gorda Ridge. Province B is restricted to the late Pleistocene sediments of western Cascadia Abyssal Plain and Vancouver Valley; the most probable sediment source is Vancouver Island and vicinity. Sandy sediments from the island no longer reach the deep-sea environments, because they are presently being trapped behind the sills of the glacially-scoured inlets of the island. Province C includes the late Pleistocene and Holocene deposits in southeastern Cascadia Basin and Cascadia Channel; the sediments were derived from the Columbia River drainage. During Holocene time, the supply of coarse-grained detritals from the Columbia River diminished as sea level rose, and locally derived sediments from the metamorphic terrane of the Klamath Mountains were deposited at the base of the continental slope off southern Oregon and northern California (Province D), overriding the influence of the Columbia River sedimentation.

Sedimentation in Cascadia Deep-Sea Channel

Cascadia Channel is the most extensive deep-sea channel known in the Pacific Ocean and extends across Cascadia Basin, through Blanco Fracture Zone, and onto Tufts Abyssal Plain. The channel is believed to be more than 2200 km in length and has a gradually decreasing gradient averaging 1:1000. Maximum channel relief reaches 300 m on the abyssal plain and 1100 m in the mountains of the fracture zone. The right (north and west) bank is consistently about 30 m higher than the left (south and east). Turbidity currents have deposited thick, olive-green silt sequences throughout upper and lower Cascadia Channel during Holocene time. The sediment is derived primarily from the Columbia River and is transported to the channel through Willapa Canyon. A cyclic alternation of the silt sequences and thin layers of hemipelagic gray clay extends at least 650 km along the channel axis. Similar Holocene sequences which are thinner and finer grained, occur on the walls and levees of the upper channel and indicate that turbidity currents have risen high above the channel floor to deposit their characteristic sediments. A thin surficial covering of Holocene sediment along the middle channel demonstrates the erosional or non-depositional nature of the turbidity currents in this area. The Holocene turbidity current deposits are graded texturally and compositionally, and contain Foraminifera from neritic, bathyal, and abyssal depths which have been size-sorted. A sequence of sedimentary structures occurs in the deposits similar to that found by Bouma in turbidites exposed on the continent. There is a sharp break in the textural and compositional properties of each graded bed. The coarser grained, basal zone of each bed represents deposition from the traction load; the finer grained, organic-rich, upper portion of each graded bed represents deposition from the suspension load. Individual turbidity current sequences are thinnest in the upper and thickest in the lower channel. Recurrence intervals between flows range from 400 years in the upper to 1500 years along portions of the lower channel. Evidently each flow recorded near shore did not extend its entire length. Turbidity currents have reached heights of at least 117 m and spread laterally 17 km from the channel axis. Calculated flow velocities range from 5.8 m/sec along the upper channel to 3.3 m/sec along the lower portion. Pleistocene turbidity currents within Cascadia Basin were much more extensive areally than the Holocene flows, and they deposited sediment which was coarser and cleaner. Pronounced levees which border the upper channel are due chiefly to Pleistocene overflow. Coarse gravels and ice-rafted pebbly clays were also deposited along Cascadia Channel during Pleistocene time.

Deep-sea sedimentation and sediment-fauna interaction in Cascadia Channel and on Cascadia Abyssal Plain

The transport of sediments from shallow water by turbidity currents and their deposition within Cascadia Channel in the northeast Pacific Ocean have created a unique environment. Thick organic-rich turbidity current deposits of postglacial age in Cascadia Channel contrast markedly to the thin, less rich, hemipelagic clays overlying clean late Pleistocene sands on the adjacent abyssal plain to either side. The benthic animal population in the channel is four times as abundant as that of the adjacent plain. Burrowing organisms in Cascadia Channel have left many well-preserved burrows of distinct sizes and shapes within the successive turbidity current deposits. A variation in the depth and the frequency of burrowing within these deposits has been recognized and correlated over a distance of 65 km within Cascadia Channel. It is postulated that the turbidity flows create a unique environment in the channel and that the fauna is affected by differences in sediment size and composition and by the increased supply of utilizable organic material.

Influence of Cascadia Channel on Abyssal Sedimentation: ABSTRACT

Cascadia channel is the most prominent and extensive deep-sea channel known in the northeastern Pacific Ocean. Preliminary results from a survey of this channel in the part of Cascadia abyssal plain off the Oregon coast and in the seamount province west of the plain are presented. The bottom of the channel has a depth range of 1,565-1,830 fathoms and a slope of about 1:1,000. Relief ranges from 20 fathoms off northern Oregon to more than 400 fathoms in an abyssal gap in the seamount province. The width of the channel ranges from 1 to 4 nautical miles at the top and from less than ¼ to about 3 miles at the bottom. Piston cores taken along a 6-mile profile extending from the western side (abyssal plain) to the eastern side (Astoria fan) of Cascadia channel exhibit a marked diversity in sediment texture and composition. On the western side the sediments are composed chiefly of gray clay interbedded with thin laminations of sandy silt. Planktonic Foraminifera predominate in the sandy material. Sediments in the axis of the channel consist of several cyclic depositional units. Each unit is made up of a basal fine sand grading upward into olive-brown silt and clay and overlain by gray clay. The sand and silt contain detrital minerals and organic debris derived from continental sources. On the eastern side the sediments are similar to terrigenous material found elsewhere on Astoria fan. Sedimentation on Cascadia abyssal plain is controlled, to a large extent, by Cascadia channel. The channel apparently acts as a sediment trap and as an avenue of dispersal for terrigenous material transported along the sea floor. End_of_Article - Last_Page 649------------