Cascadia Channel

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

Contents

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

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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.

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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). United States Geological Survey. 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.
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