Cascadia Channel is the most extensive

deep-sea channel Abyssal channels (also, deep-sea channels, underwater channels) are Channel (geography), channels in Earth's sea floor. They are formed by fast-flowing floods of Turbidity current, turbid water caused by avalanches near the channel's head, with ...

currently known (as of 1969) of the

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

. It extends across Cascadia Abyssal Plain, through the

Blanco Fracture Zone The Blanco Fracture Zone or Blanco Transform Fault Zone (BTFZ) is a right lateral transform fault zone, which runs northwest off the coast of Oregon in the Pacific Northwest of the United States, extending from the Gorda Ridge in the south to the ...

, and into Tufts Abyssal Plain. Notably, Cascadia Channel has tributaries, akin to river tributaries. Cascadia Channel has two contributing tributaries—

Juan de Fuca Channel Juan de Fuca Channel is a submarine channel off the shore of Washington state, United States and the Strait of Juan de Fuca. The geography of Juan de Fuca Channel The Juan de Fuca Channel is a submarine canyon running from the shelf break, o ...

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-Baptis ...

and Willapa Channels in the south. The channel 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 spreading center and divergent plate boundary located off the coast of the Pacific Northwest region of North America. The ridge separates the Pacific Plate to the west and the Juan de Fuca Plate to the east ...

, which was actively spreading. In the late

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

, the

volcanic A volcano is a rupture 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 found where tectonic plates a ...

basement was covered by transparent

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

and

hemipelagic Hemipelagic sediment, or hemipelagite, is a type of marine sediment that consists of clay and silt-sized grains that are terrigenous and some biogenic material derived from the landmass nearest the deposits or from organisms living in the water. He ...

sediment, which horizontally deposited

turbidites A turbidite is the geologic 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 Turbidites were ...

covered. During late

Pleistocene glaciation The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describe ...

and the lowering of

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

, much

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

and

gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifi ...

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

turbidity current 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. T ...

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

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

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's bed or the valley's floor. T ...

. 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 The Astoria Fan is a submarine fan. It has sediment, radiating asymmetrically southward from the mouth of the Astoria Canyon. From Astoria Canyon's mouth, the fan extends about to its western end, which is the Cascadia Channel. The fan proper en ...

. During the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

, turbidity current from the

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

sediment continued to flow, both down the Cascade channel and the

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 ancient Greek, βένθος (bénthos), meaning "t ...

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 water quality. Fluids can ...

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 5 km, from c ...

there may be a

sediment flow Sediment transport is the movement of solid particles (sediment), typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained. Sediment transport occurs in natural systems ...

, 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 Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...

evidence for the occurrence of earthquakes on the

Cascadia Subduction Zone The Cascadia subduction zone is a convergent plate boundary that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and ...

is off

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

and

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...

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

Earthquakes An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

can set off

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

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. T ...

. In 1990, John Adams of the

Geological Survey of Canada The Geological Survey of Canada (GSC; french: Commission géologique du Canada (CGC)) is a Canadian federal government agency responsible for performing geological surveys of the country, developing Canada's natural resources and protecting the en ...

suggested that these turbidity currents originated during great subduction zone

earthquakes An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

. 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 (''Giiwas'' in the Native American language Klamath language, Klamath) is a complex volcano in the state of Oregon, United States, in a segment of the Cascade Volcanoes, Cascade Volcanic Arc and Cascade Range. Most of the mountai ...

, which gave modern-day

its

Crater Lake Crater Lake (Klamath language, Klamath: ''Giiwas'') 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 famous for its deep blue color and water clarity. The ...

, 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 island ...

and

submarine canyons 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 5 km, from ...

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 ve ...

Astoria Canyon Astoria Canyon is a submarine canyon 10 miles (16 km) offshore from the mouth of the Columbia River. See also * Astoria Fan The Astoria Fan is a submarine fan. It has sediment, radiating asymmetrically southward from the mouth of th ...

* Barkely Canyon * Cascadia Channel *

Clayoquot Canyon Clayoquot is an anglicization of the Nuu-chah-nulth language name "Tla-o-qui-aht", one of the indigenous tribes of the region so named. It may refer to: * Clayoquot, British Columbia, historically also known as Port Cox, a community on Stubbs Isla ...

* Father Charles Canyon *

Grays Canyon Grays or Greys may refer to: Places * Grays Bay, Nunavut, Canada * Grays, Essex, a town in Essex, England ** Grays railway station ** Grays School * Grays, Kent, a hamlet in Kent, England * Rotherfield Greys or Greys, a village in Oxfordshire, En ...

Guide Canyon A guide is a person who leads travelers, sportspeople, or tourists through unknown or unfamiliar locations. The term can also be applied to a person who leads others to more abstract goals such as knowledge or wisdom. Travel and recreation Ex ...

Juan de Fuca Canyon Juan de Fuca Channel is a submarine channel off the shore of Washington state, United States and the Strait of Juan de Fuca. The geography of Juan de Fuca Channel The Juan de Fuca Channel is a submarine canyon running from the shelf break, o ...

* Juan de Fuca Plate *

Loudon Canyon Loudon may refer to: Places In the United States: *Loudon, Massachusetts, formerly a constituent part of Otis, Massachusetts *Loudon, New Hampshire **Loudon (CDP), New Hampshire *Loudon, Tennessee *Loudon County, Tennessee *Loudoun County, Virgin ...

Nitinat Canyon Ditidaht (also Nitinaht, Nitinat, Southern Nootkan) or diitiidʔaaʔtx̣ is a South Wakashan (Nootkan) language spoken on the southern part of Vancouver Island. Nitinaht is related to the other South Wakashan languages, Makah and the neighboring ...

Nitinat Fan Ditidaht (also Nitinaht, Nitinat, Southern Nootkan) or diitiidʔaaʔtx̣ is a South Wakashan (Nootkan) language spoken on the southern part of Vancouver Island. Nitinaht is related to the other South Wakashan languages, Makah and the neighboring ...

Quileute Canyon Quileute Canyon (also ''Quillayute Canyon'') is a submarine canyon, off of Washington state, United States. Its location It is just north of Quinault Canyon. Quileute Canyon is offshore, from both La Push and Forks. Quillayute River pours into ...

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, opposit ...

Willapa Canyon Willapa may refer to: * Willapa people, an Athapaskan-speaking people in Washington, United States * Willapa River, river on the Pacific coast of southwestern Washington, United States * ''General Miles'', a ship * Willapa Electric Company, an e ...

References

{{Reflist

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
Geography of the Pacific Northwest Submarine canyons of the Pacific Ocean Coastal and oceanic landforms Submarine topography Marine geology