Cascadia Channel is the most extensive deep-sea channel currently known (as of 1969) of the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

. It extends across Cascadia Abyssal Plain, through the Blanco fracture zone, and into Tufts Abyssal Plain. Notably, Cascadia Channel has tributaries, akin to river tributaries..The Channel has two contributing tributaries— Juan de Fuca Channel from the north, and the outflow of

Quinault Quinault may refer to: * Quinault people, an Indigenous people of the Pacific Northwest Coast **Quinault Indian Nation, a federally recognized tribe ** Quinault language, their language People * Quinault family of actors, including: * Jean-Bapt ...

and Willapa Channels in the south. It is believed to be over long.

Formation

Headed north-south, Cascadia Channel initially formed on the eastern flank of the

Juan de Fuca Ridge The Juan de Fuca Ridge is a Mid-ocean ridge, mid-ocean spreading center and divergent plate boundary located off the coast of the Pacific Northwest region of North America, named after Juan de Fuca. The ridge separates the Pacific Plate to the we ...

, which was actively spreading. In the late

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

, the

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

basement was covered by seismically transparent

pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

and hemipelagic sediment, which horizontally deposited

turbidites A turbidite is the geologic Deposition (geology), deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing ...

covered. During late Pleistocene glaciation and the lowering of

sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

, much

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

and

gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...

from the shore deposited on either the upper slope or the outer shelf, which initiated

turbidity current A turbidity current is most typically an Ocean current, underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that water-saturated sediment may be the primary actor in ...

s, converting the lower and middle portions of the channel into

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

al features. This led to the initiation of

downcutting Downcutting, also called erosional downcutting, downward erosion or vertical erosion, is a geological process by hydraulic action that deepens the channel of a stream or valley by removing material from the stream bed or the valley floor. The ...

. At this time, apparently the channel built up by turbidity current that proceeded south, along the western part of the Cascadia abyssal plain, also from the west of the Astoria Fan. During the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

, turbidity current from the

Columbia River The Columbia River (Upper Chinook language, Upper Chinook: ' or '; Sahaptin language, Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river headwater ...

sediment continued to flow, both down the Cascade channel and the Blanco fracture zone.

Marine Biology

In the channel, the

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

animal population is four times as abundant compared to the surrounding Juan de Fuca plate. In Cascadia Channel, burrowing organisms have left many well-preserved burrows of distinct sizes and shapes in

turbidity Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of both water clarity and wa ...

current deposits.

Turbidite Flows

An earthquake can trigger a turbidite flow, and these are likely to record a succession of submarine mass movements. At the head of a

submarine canyon A submarine canyon is a steep-sided valley cut into the seabed of the continental slope, sometimes extending well onto the continental shelf, having nearly vertical walls, and occasionally having canyon wall heights of up to , from canyon flo ...

there may be a sediment flow, which may begin as a slide or slump, continue as a debris flow, and change into a turbidity current as fluid content increases down slope.

Geologic Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth s ...

evidence for the occurrence of earthquakes on the

Cascadia subduction zone The Cascadia subduction zone is a convergent plate boundary, about off the Pacific coast of North America, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ m ...

is off

Oregon Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...

and

Washington Washington most commonly refers to: * George Washington (1732–1799), the first president of the United States * Washington (state), a state in the Pacific Northwest of the United States * Washington, D.C., the capital of the United States ** A ...

, and includes sedimentary deposits that have been observed in cores from deep-sea channels and abyssal fans.

Earthquakes An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they c ...

can set off

submarine A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or infor ...

mass movements that can initiate

turbidity currents A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that water-saturated sediment may be the primary actor in the process. ...

. In 1990, John Adams of the

Geological Survey of Canada The Geological Survey of Canada (GSC; , CGC) is a Canadian federal government agency responsible for performing geological surveys of the country developing Canada's natural resources and protecting the environment. A branch of the Earth Science ...

suggested that these turbidity currents originated during great

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

zone

earthquakes An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they c ...

. There is a consistent number of

in core samples from both side and main channels, indicating that each turbidity current was likely caused at the same time, by the same event which may be the

1700 Cascadia earthquake The 1700 Cascadia earthquake occurred along the Cascadia subduction zone on January 26, 1700, with an estimated moment magnitude of 8.7–9.2. The megathrust earthquake involved the Juan de Fuca plate from mid-Vancouver Island, south along the P ...

. Of the turbidites, large storms are not the likely source. Ash from the eruption of

Mount Mazama Mount Mazama ( Klamath: ''Tum-sum-ne'') is a complex volcano in the western U.S. state of Oregon, in a segment of the Cascade Volcanic Arc and Cascade Range. The volcano is in Klamath County, in the southern Cascades, north of the Oregon– ...

, which gave modern-day

its

Crater Lake Crater Lake ( Klamath: ) is a volcanic crater lake in south-central Oregon in the Western United States. It is the main feature of Crater Lake National Park and is a tourist attraction for its deep blue color and water clarity. T ...

, reached Cascadia Channel via the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an islan ...

and submarine canyons.

Local geography

Abyssal fan Abyssal fans, also known as deep-sea fans, underwater deltas, and submarine fans, are underwater geological structures associated with large-scale sediment deposition and formed by turbidity currents. They can be thought of as an underwater v ...

Astoria Canyon Astoria Canyon is a submarine canyon 10 miles (16 km) offshore from the mouth of the Columbia River The Columbia River (Upper Chinook language, Upper Chinook: ' or '; Sahaptin language, Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana'' ...

* Astoria Fan * Barkely Canyon * Cascadia Channel *

* Clayoquot Canyon * Father Charles Canyon * Grays Canyon * Guide Canyon * Juan de Fuca Canyon * Juan de Fuca plate * Juan de Fuca Channel * Loudon Canyon * Nitinat Canyon * Nitinat Fan * Quileute Canyon *

Quinault Canyon The Quinault Canyon is a submarine canyon, off Washington state, in Olympic Coast National Marine Sanctuary. The area It lies opposite the Quinault Reservation. From the map, it is clear the Quinault River drains into the Pacific Ocean, oppo ...

* Willapa Canyon

References

External links and references

Undersea Features page
* tp://ehzftp.wr.usgs.gov/skirby/Marine%20Geohazards%20Workshop%20Documents/1Aiiiss_Atwater_Turbidites_NMGW_2011.pdf One link, an FTP
Cascadia Paleoseismic History Based on Turbidite Stratigraphy
{coord, 43, 30, 00, N, 130, 00, 00, W, source:wikidata, display=title Geography of the Pacific Northwest Submarine canyons of the Pacific Ocean Coastal and oceanic landforms Submarine topography Marine geology