Cascadia Channel

Last updated

Cascadia Channel is the most extensive deep-sea channel currently known (as of 1969) of the Pacific Ocean. It extends across Cascadia Abyssal Plain, through the Blanco Fracture Zone, and into Tufts Abyssal Plain. [1] Notably, Cascadia Channel has tributaries, akin to river tributaries. [2]

Contents

Cascadia Channel has two contributing tributaries—Juan de Fuca Channel from the north, and the outflow of Quinault and Willapa Channels in the south. [2] The channel is believed to be over 2,200 kilometres (1,400 mi) long. [1]

Formation

Headed north-south, Cascadia Channel initially formed on the eastern flank of the Juan de Fuca Ridge, which was actively spreading. In the late Cenozoic, the volcanic basement was covered by transparent pelagic and hemipelagic sediment, which horizontally deposited turbidites covered. During late Pleistocene glaciation and the lowering of sea level, much sand and gravel from the shore deposited on either the upper slope or the outer shelf, which initiated turbidity currents, converting the lower and middle portions of the channel into erosional features. This led to the initiation of downcutting. 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, turbidity current from the Columbia River sediment continued to flow, both down the Cascade channel and the Blanco Fracture Zone. [3]

Marine Biology

In the channel, the benthic 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 current deposits. [4]

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 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 evidence for the occurrence of earthquakes on the Cascadia Subduction Zone is off Oregon and Washington, and includes sedimentary deposits that have been observed in cores from deep-sea channels and abyssal fans.

Earthquakes can set off submarine mass movements that can initiate turbidity currents. [2]

In 1990, John Adams of the Geological Survey of Canada suggested that these turbidity currents originated during great subduction zone earthquakes. There is a consistent number of turbidites 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.

Of the turbidites, large storms are not the likely source. [5]

Ash from the eruption of Mount Mazama, which gave modern-day Oregon its Crater Lake, reached Cascadia Channel via the continental shelf and submarine canyons. [2]

Local geography

Related Research Articles

<span class="mw-page-title-main">Juan de Fuca Plate</span> Small tectonic plate in the eastern North Pacific

The Juan de Fuca Plate is a small tectonic plate (microplate) generated from the Juan de Fuca Ridge that is subducting beneath the northerly portion of the western side of the North American Plate at the Cascadia subduction zone. It is named after the explorer of the same name. One of the smallest of Earth's tectonic plates, the Juan de Fuca Plate is a remnant part of the once-vast Farallon Plate, which is now largely subducted underneath the North American Plate.

<span class="mw-page-title-main">Turbidite</span> Geologic deposit of a turbidity current

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.

<span class="mw-page-title-main">Cascadia subduction zone</span> Convergent plate boundary that stretches from northern Vancouver Island to Northern California

The Cascadia subduction zone is a 960 km fault at a convergent plate boundary, about 112-160 km off the Pacific Shore, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ magnitude earthquakes and tsunamis that could reach 30m. The Oregon Department of Emergency Management estimates shaking would last 5-7 minutes along the coast, with strength and intensity decreasing further from the epicenter. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and Gorda plates move to the east and slide below the much larger mostly continental North American Plate. The zone varies in width and lies offshore beginning near Cape Mendocino, Northern California, passing through Oregon and Washington, and terminating at about Vancouver Island in British Columbia.

<span class="mw-page-title-main">Submarine canyon</span> Steep-sided valley cut into the seabed of the continental slope

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 (3 mi), from canyon floor to canyon rim, as with the Great Bahama Canyon. Just as above-sea-level canyons serve as channels for the flow of water across land, submarine canyons serve as channels for the flow of turbidity currents across the seafloor. Turbidity currents are flows of dense, sediment laden waters that are supplied by rivers, or generated on the seabed by storms, submarine landslides, earthquakes, and other soil disturbances. Turbidity currents travel down slope at great speed, eroding the continental slope and finally depositing sediment onto the abyssal plain, where the particles settle out.

<span class="mw-page-title-main">Turbidity current</span> An underwater current of usually rapidly moving, sediment-laden water moving down a slope

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. Turbidity currents can also occur in other fluids besides water.

<span class="mw-page-title-main">Abyssal fan</span> Underwater geological structures associated with large-scale sediment deposition

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 version of alluvial fans and can vary dramatically in size, with widths from several kilometres to several thousands of kilometres. The largest is the Bengal Fan, followed by the Indus Fan, but major fans are also found at the outlet of the Amazon, Congo, Mississippi and elsewhere.

<span class="mw-page-title-main">Gorda Ridge</span> Tectonic spreading center off the northern coast of California and southern Oregon

The Gorda Ridge, aka Gorda Ridges tectonic spreading center, is located roughly 200 kilometres (120 mi) off the northern coast of California and southern Oregon. Running NE – SW it is roughly 300 kilometres (190 mi) in length. The ridge is broken into three segments; the northern ridge, central ridge, and the southern ridge, which contains the Escanaba Trough.

<span class="mw-page-title-main">Blanco Fracture Zone</span> Geological fault zone off the Oregon coast in the US

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 Juan de Fuca Ridge in the north.

<span class="mw-page-title-main">Geology of the Pacific Northwest</span> Geology of Oregon and Washington (United States) and British Columbia (Canada)

The geology of the Pacific Northwest includes the composition, structure, physical properties and the processes that shape the Pacific Northwest region of North America. The region is part of the Ring of Fire: the subduction of the Pacific and Farallon Plates under the North American Plate is responsible for many of the area's scenic features as well as some of its hazards, such as volcanoes, earthquakes, and landslides.

Abyssal channels are channels in Earth's sea floor. They are formed by fast-flowing floods of turbid water caused by avalanches near the channel's head, with the sediment carried by the water causing a build-up of the surrounding abyssal plains. Submarine channels and the turbidite systems which form them are responsible for the accumulation of most sandstone deposits found on continental slopes and have proven to be one of the most common types of hydrocarbon reservoirs found in these regions.

<span class="mw-page-title-main">Northwest Atlantic Mid-Ocean Channel</span> Hudson Strait area undersea channels

The Northwest Atlantic Mid-Ocean Channel (NAMOC) is the main body of a turbidity current system of channels and canyons running on the sea bottom from the Hudson Strait, through the Labrador Sea and ending at the Sohm Abyssal Plain in the Atlantic Ocean. Contrary to most other such systems which fan away from the main channel, numerous tributaries run into the NAMOC and end there. The density of those tributaries is the highest near the Labrador Peninsula, but the longest tributary, called Imarssuak Mid-Ocean Channel (IMOC), originates in the Atlantic Ocean.

Ocean Networks Canada is a world-leading research and ocean observing facility hosted and owned by the University of Victoria, and managed by the not-for profit ONC Society. ONC operates unparalleled observatories in the deep ocean and coastal waters of Canada’s three coasts–the Arctic, the Pacific and the Atlantic–gathering biological, chemical, geological and physical data to drive solutions for science, industry and society. ONC operates the NEPTUNE and VENUS cabled ocean observatories in the northeast Pacific Ocean and the Salish Sea. Additionally, Ocean Networks Canada operates smaller community-based observatories offshore from Cambridge Bay, Nunavut., Campbell River, Kitamaat Village and Digby Island. These observatories collect data on physical, chemical, biological, and geological aspects of the ocean over long time periods. As with other ocean observatories such as ESONET, Ocean Observatories Initiative, MACHO and DONET, scientific instruments connected to Ocean Networks Canada are operated remotely and provide continuous streams of freely available data to researchers and the public. Over 200 gigabytes of data are collected every day.

<span class="mw-page-title-main">Congo Canyon</span> African submarine canyon at the end of the Congo River

Congo Canyon is a submarine canyon found at the end of the Congo River in Africa. It is one of the largest submarine canyons in the world.

<span class="mw-page-title-main">Quinault Canyon</span> Submarine canyon in the Pacific Ocean near Washington, United States

The Quinault Canyon is a submarine canyon, off Washington state, in Olympic Coast National Marine Sanctuary.

<span class="mw-page-title-main">Juan de Fuca Channel</span> Submarine channel off the shore of Washington state

<span class="mw-page-title-main">Aleutian subduction zone</span> Convergence boundary between the North American Plate and the Pacific Plate

The Aleutian subduction zone is a 2,500 mi (4,000 km) long convergent boundary between the North American Plate and the Pacific Plate, that extends from the Alaska Range to the Kamchatka Peninsula. Here, the Pacific Plate is being subducted underneath the North American Plate and the rate of subduction changes from west to east from 7.5 to 5.1 cm per year. The Aleutian subduction zone includes two prominent features, the Aleutian Arc and the Aleutian Trench. The Aleutian Arc was created via volcanic eruptions from dehydration of the subducting slab at ~100 km depth. The Aleutian Trench is a narrow and deep morphology that occurs between the two converging plates as the subducting slab dives beneath the overriding plate.

Madeira Abyssal Plain, also called Madeira Plain, is an abyssal plain situated at the center and deepest part of the Canary Basin. It is a north-northeast to south-southeast elongated basin that almost parallels the Mid-Atlantic Ridge. Its western boundary is marked by a chain of seamounts known as the either Seewarte Seamounts or Atlantis-Great Meteor Seamount Chain. Its eastern boundary is a distinct break of slope that marks the foot of the African Continental Rise. This abyssal plain occupies an area of about 68,000 km2 (26,000 sq mi). Across this basin, slope angles are generally less than 0.01°.

The Kaikōura Canyon is a geologically active submarine canyon located southwest of the Kaikōura Peninsula off the northeastern coast of the South Island of New Zealand. It is 60 kilometres (37 mi) long, and is generally U-shaped. The canyon descends into deep water and merges into an ocean channel system that can be traced for hundreds of kilometres across the deep ocean floor. At the head of the Kaikōura Canyon, the depth of water is around 30 metres (98 ft), but it drops rapidly to 600 metres (2,000 ft) and continues down to around 2,000 metres (6,600 ft) deep where it meets the Hikurangi Channel. Sperm whales can be seen close to the coast south of Goose Bay, because the deep water of the Kaikōura Canyon is only one kilometre (0.62 mi) off the shoreline in this area.

References

  1. 1 2 Gary Bruce Griggs. "Cascadia Channel: The Anatomy of a Deep-Sea Channel" (PDF). Retrieved 4 September 2017.
  2. 1 2 3 4 Brian F. Atwater and Gary B. Griggs (2012). "Deep-Sea Turbidites as Guides to Holocene Earthquake History at the Cascadia Subduction Zone— Alternative Views for a Seismic-Hazard Workshop" (PDF). USGS. Retrieved 11 September 2017.
  3. ↑ Gary B. Griggs (September 20, 1973). "Origin and Development of Cascadia Deep-Sea Channel". Journal of Geophysical Research . 78 (27): 6325–6339. Bibcode:1973JGR....78.6325G. doi:10.1029/JC078i027p06325.
  4. ↑ G.B.Griggs, A.G.CareyJr., L.D.Kulm (April 1969). "Deep-sea sedimentation and sediment-fauna interaction in Cascadia Channel and on Cascadia Abyssal Plain". Deep Sea Research and Oceanographic Abstracts. 16 (2): 157–166. Bibcode:1969DSRA...16..157G. doi:10.1016/0011-7471(69)90071-0.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ↑ "Turbidite evidence". Pacific Northwest Seismic Reference. Retrieved 14 September 2017.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.