“Cascadia Channel”的意思、由来-开放百科全书

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]

How Cascadia Channel formed

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]

Its size

Life in Cascadia Channel

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]

Its relationship to earthquakes

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.

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.

It has sediment from the eruption of Mount Mazama

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

References

1. ^¹{{cite web | url=http://activetectonics.coas.oregonstate.edu/paper_files/GriggsThesisSmallall.pdf | title=Cascadia Channel: The Anatomy of a Deep-Sea Channel | accessdate=4 September 2017 | author=Gary Bruce Griggs}}
2. ^¹²³{{cite web | url=https://pubs.usgs.gov/of/2012/1043/of2012-1043.pdf | title=Deep-Sea Turbidites as Guides to Holocene Earthquake History at the Cascadia Subduction Zone— Alternative Views for a Seismic-Hazard Workshop | publisher=USGS | date=2012 | accessdate=11 September 2017 | author=Brian F. Atwater and Gary B. Griggs}}
3. ^{{cite journal | title=Origin and Development of Cascadia Deep-Sea Channel | journal=Journal of Geophysical Research | date=September 20, 1973 | author=Gary B. Griggs | doi=10.1029/JC078i027p06325 | bibcode=1973JGR....78.6325G | volume=78 |issue = 27| pages=6325–6339}}
4. ^{{cite journal | url=http://www.sciencedirect.com/science/article/pii/0011747169900710 | title=Deep Sea Research and Oceanographic Abstracts | journal=Deep Sea Research and Oceanographic Abstracts | date=April 1969 | accessdate=5 September 2017 | author=G.B.Griggs, A.G.CareyJr., L.D.Kulm | pages=157–166 | doi=10.1016/0011-7471(69)90071-0 | volume=16| issue=2 }}
5. ^{{cite web | url=https://pnsn.org/outreach/earthquakesources/CSZ/turbiditeevidence | title=Turbidite evidence | publisher=Pacific Northwest Seismic Reference | accessdate=14 September 2017}}