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The Vashon Glaciation or Vashon Stade was the most recent period of cold climate and advanced glaciation in the western part of present-day Washington State.〔http://www.historylink.org/index.cfm?DisplayPage=output.cfm&file_id=5087 Historylink.org - Jennifer Ott - Retreating glaciers create Puget Sound and Grand Coulee as the Ice Age ends about 15,000 years ago.〕 It lasted from about 20,000 - 15,000 BP (18,050 - 13,050 BCE).〔http://pubs.usgs.gov/sir/2010/5254/pdf/sir20105254_chap2.pdf The Geomorphic Setting of Puget Sound: Implications for Shoreline Erosion and the Impacts of Erosion Control Structures〕 It was one of the phases of the Fraser Glaciation, which occurred during the latter part of the last glacial period. The Cordilleran Ice Sheet was an ice sheet that covered present-day southern Alaska and parts of western Canada. During the Vashon Glaciation, the Cordilleran Ice Sheet advanced into the Puget Sound region. ==The Advance== The Advance During the Vashon Glaciation, the Cordilleran Ice Sheet grew and advanced southwards at a rate of about 135 meters (440 feet) per year.〔〔 It crossed the present-day Canada–United States border around 19,000 BP (17,050 BCE).〔http://www.youtube.com/watch?v=YHWMHzi_deg Vashon Glaciation Animation〕 The glacier reached its maximum extent in the vicinity of the present-day city of Tenino〔http://www.dnr.wa.gov/programs-and-services/geology/explore-popular-geology/geologic-provinces-washington/puget-lowland WA State Dept. of Natural Resources - Puget Lowland〕 around 16,950 BP (15,000 BCE).〔http://faculty.washington.edu/tswanson/ESS/Research/QR%2098%20205-213.pdf University of Washington - Stephen C. Porter and Terry W. Swanson - Radiocarbon Age Constraints on Rates of Advance and Retreat of the Puget Lobe of the Cordilleran Ice Sheet during the Last Glaciation〕 The Maximum Extent The Cordilleran Ice Sheet remained at its maximum extent in the vicinity of present-day Tenino from around 16,950 BP (15,000 BCE) to around 16,850 BP (14,900 BCE), a total of about 100 years.〔 The ice depths were about 1,600 meters (5,250 feet) at the present-day Canada–United States border, 1,000 meters (3,300 feet) in Seattle, and 200 meters (650 feet) at the glacier's terminus in the Tenino area.〔 Climate From around 20,000 - 16,000 BP (18,050 – 14,050 BCE), annual mean temperatures in the southern Puget Sound region were about 5-7 °C (9-13 °F) colder than in present times (present times as of 1990), and precipitation was around 1 meter (39 inches) less.〔http://www.fs.fed.us/rm/pubs/rmrs_gtr292/1992_whitlock.pdf University of Washington – Cathy Whitlock - Vegetational and Climatic History of the Pacific Northwest during the Last 20,000 Years: Implications for Understanding Present-day Biodiversity〕 The low precipitation was caused by the Laurentide Ice Sheet,〔 an ice sheet covering much of Canada, and parts of the northern United States in the midwest and east. It split the jet stream over North America in two.〔 The southern branch was pushed further south than it is in present times.〔 The winter storm tracks instead were hitting places further south, thus missing present-day Washington State most of the time.〔 Because of this, Southern and Central California had wetter climates than in present times.〔http://geochange.er.usgs.gov/sw/impacts/biology/pastclim/ U.S. Geological Survey - Robert S. Thompson - Past Climate and Vegetation Changes in the Southwestern United States〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Vashon Glaciation」の詳細全文を読む スポンサード リンク
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