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Cook Inlet
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==Geography== [[File:Wavesclamgulch.jpg|thumb|left|Cook Inlet seen from [[Clam Gulch]]]] Cook inlet, along with the [[Kenai Peninsula]], the [[Kenai Mountains]], the [[Chugach Mountains]], and [[Kodiak Island]], formed approximately 65 million years ago, just after the extinction of the dinosaurs. Like most of Alaska's mountains, they consist mainly of [[sedimentary rock]] and [[metamorphic rock]] that were deposited on the ocean floor during the [[Cretaceous period]]. This area, where a corner of the [[Pacific Plate]] subducts under the [[North American Plate]], uplifted the ocean floor and compressed it, causing the crust to thicken and [[Orogeny|scrunch]]. Tectonic forces lifted the mountains and peninsula out of the water, forming a valley that was cut off from the ocean to the north and the west. The rest of Alaska's mountains were formed in the same manner, in cyclic events, and the mountain ranges become progressively older the further north they lie. Thus, the Cook Inlet and its surrounding land masses are rather young compared to those of the [[Alaska Range]], which formed around 126 million years ago, or the [[Brooks Range]] which formed around 256 million years ago. The valley left by this continental compaction remains open to the [[Gulf of Alaska]] to the south, forming the inlet as it exists today. The surrounding mountains were host the large ice sheets and glaciers during the [[Pleistocene epoch]] (the Ice Ages, around 2 million to 11,000 years ago) which scoured the land and formed vast plains and [[moraine]]s surrounding much of the upper inlet from [[glacial till]] that was deposited.<ref name=":0" /><ref>[https://www.usgs.gov/media/images/detailed-geologic-map-view-anchorage-ak USGS Detailed Geologic Map View of Anchorage, AK]</ref><ref>{{cite encyclopedia |url=https://www.britannica.com/place/Alaskan-Mountains |encyclopedia=Encyclopedia Britannica |title=Alaskan mountains |edition=Online |access-date=January 24, 2024}}</ref> Cook Inlet exists in a [[subsidence]] zone which contains many [[Fault (geology)|faults]], and is frequently prone to [[earthquake]] activity. The primary fault, the Aleutian Fault, is found in the nearby [[Aleutian Trench]] in the Gulf of Alaska, where a corner of the Pacific Plate is forced underneath Alaska at a 45-degree angle. Thus, most of the uplift force occurs along a line from Kodiak Island and up the Kenai Mountains to the Chugach mountains. The inlet lies in a region where the crust is wrinkled under this force and the tectonic forces push the ground downward. In 1964, the [[1964 Alaska earthquake]], a [[megathrust earthquake]], occurred when over 600 miles of the Aleutian fault ruptured, uplifting the Kenai Mountains 60 feet (20 meters) in under 5 minutes. With a magnitude of 9.2, the earthquake was the fourth largest ever recorded. It devastated Anchorage where much of downtown dropped several stories, and the mountains surrounding the Turnagain Arm subsided 8 feet (2.4 meters), submerging the towns of [[Portage, Alaska|Portage]] and [[Girdwood, Alaska|Girdwood]], as well as long stretches of the [[Seward Highway]].<ref>[https://earthquake.usgs.gov/earthquakes/events/alaska1964/ USGS M9.2 Alaska Earthquake and Tsunami of March 27, 1964]</ref> [[File:Map of Alaska Volcanoes 1.gif|thumb|Locations of volcanoes near Cook Inlet]] Because it lies along a [[subduction zone]], the Cook Inlet region contains active volcanoes, including [[Augustine Volcano]] and [[Mount Redoubt]], and is part of the [[Pacific Ring of Fire]]. Hot magma and steam from the subducting ocean floor build up within these volcanoes, which tend to erupt in fairly regular cycles with very explosive force, often spewing volcanic ash tens of thousands of feet (several kilometers) high. Volcanic [[eruption]]s in the region have been associated with [[earthquake]]s and [[tsunami]]s, and debris [[avalanche]]s have resulted in tsunamis also.<ref>{{cite web |url = http://volcano.und.edu/vwdocs/volc_images/north_america/alaska/august.html |title = Augustine, Cook Inlet, Alaska |access-date = 2007-02-03 |url-status = dead |archive-url = https://web.archive.org/web/20070204075005/http://volcano.und.edu/vwdocs/volc_images/north_america/alaska/august.html |archive-date = 2007-02-04 }}</ref> There was an earthquake of the magnitude of 7.1 on December 31, 1901 generated by an eruption that caused several tsunamis.<ref>{{cite web |url=https://earthquake.usgs.gov/regional/states/events/1901_12_31.php |title=Historic Earthquakes β Cook Inlet, Alaska |access-date=2007-02-03 }}</ref> In 2009 a [[lahar]] from Mt. Redoubt threatened the [[Drift River oil terminal]]. Cook Inlet has the fourth largest tidal range in the world. The shape of the inlet and its orientation with respect to the lunar orbit causes the tide to come in and go out very rapidly. As the inlet narrows, the speed of the water increases, creating very powerful currents with speeds of up to 6 knots (7 miles per hour). While lined with large areas of silt and [[mudflat]]s, the central and upper inlet is filled with narrow troughs that may be 150 to 300 feet (50 to 100 meters) deep. These, along with the tides, provide a challenge to ships navigating through the waters.<ref>[https://www.govinfo.gov/content/pkg/GOVPUB-I-47b721482d69e308aec1cca9b3e51955/pdf/GOVPUB-I-47b721482d69e308aec1cca9b3e51955.pdf CMI Cook Inlet Surface Current Mapping]</ref> The strong tides create powerful rip tides and bore tides which are sometimes among the largest in the world.<ref>[https://www.boem.gov/sites/default/files/boem-newsroom/Library/Publications/2000/2000_025.pdf Mapping Cook Inlet Rip Tides Using Local Knowledge and Remote Sensing]</ref> [[Tidal bores]] occur within the inlet, and especially Turnagain Arm, almost daily, but are usually too small to notice. Large bores tend to occur after extreme tidal lows, appearing as a wall of water sometimes over 10 feet high as the tide comes in all at once. Large bores are less frequent, and are typically formed during a new or full moon, especially when the moon is at [[perigee]].<ref>[https://www.alaska.org/advice/alaska-bore-tide Alaska Bore Tide]</ref> Unlike areas around the [[Bering Sea]] where weather is largely affected by sea ice, the waters of the inlet are warmed by the [[Alaska Current]] in the Gulf of Alaska, part of the North-Pacific Subpolar [[Gyre]], which affects the climate and keeps the temperatures in the Cook Inlet region fairly moderate compared to the extremes found in other parts of the state.<ref>[https://glossary.ametsoc.org/wiki/Alaska_current#:~:text=The%20eastern%20semi%20of%20the,though%20on%20a%20smaller%20scale. AMS - Glossary of Meteorology]</ref>
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