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35-567: The Vashon Glaciation lasted from about 19,000 – 16,000 BP ( Before Present – present defined as January 1, 1950 for this scale). The Cordilleran Ice Sheet was an ice sheet that covered present-day southern Alaska and parts of western Canada . The Fraser Glaciation began when the Cordilleran Ice Sheet advanced out of the mountains of British Columbia following the Fraser River and Fraser Valley . The Vashon Glaciation

70-508: A climate too warm to support glaciers, but the ice was pushing in from the north faster than it could melt. The advance of the Cordilleran Ice Sheet actually began long before 19,000 years ago. However, 19,000 years ago marks the approximate time when glaciers crossed the present-day Canada–United States border into Western Washington, which is generally considered to be the beginning of the Vashon Glaciation. This southern part of

105-597: A closed forest. The vegetation was similar to today with Alnus rubra (red alder), Picea sitchensis (sitka spruce), Pinus contorta (lodgepole pine), Pseudotsuga (Douglas fir), and Tsuga heterophylla (Western hemlock). The official end of the Pleistocene Epoch and the beginning of the Holocene Epoch occurred in 11,700 BP. Between 9,500 and 4,500 BP during the Holocene climatic optimum , temperatures in

140-421: A jumbled array of ridges and mounds form, resembling kame and kettle topography. Kettle holes can also occur in ridge shaped deposits of loose rock fragments called till . Kettle holes can form as the result of floods caused by the sudden drainage of an ice-dammed lake. These floods, called jökulhlaups , often rapidly deposit large quantities of sediment onto the sandur surface. The kettle holes are formed by

175-415: A result of blocks of dead ice left behind by retreating glaciers, which become surrounded by sediment deposited by meltwater streams as there is increased friction. The ice becomes buried in the sediment and when the ice melts, a depression is left called a kettle hole, creating a dimpled appearance on the outwash plain. Lakes often fill these kettles; these are called kettle hole lakes. Another source

210-694: Is an extension of the Fraser Glaciation in which the Cordilleran Ice Sheet advanced south of the present day Canada–United States border into the Puget Sound region. By following the Fraser Valley, the ice reached the Puget Sound Region using the same pathway that cold arctic air takes during a present-day winter cold snap. The Cordilleran, Laurentide , Innuitian, and the currently existing Greenland Ice Sheet all made up

245-410: Is less than ten meters. In most cases, kettle holes eventually fill with water, sediment, or vegetation. If the kettle is fed by surface or underground rivers or streams, it becomes a kettle lake . If the kettle receives its water from precipitation , the groundwater table, or a combination of the two, it is termed a kettle pond or kettle wetland , if vegetated. Kettle ponds that are not affected by

280-455: Is the sudden drainage of an ice-dammed lake and when the block melts, the hole it leaves behind is a kettle. As the ice melts, ramparts can form around the edge of the kettle hole. The lakes that fill these holes are seldom more than 10 m (33 ft) deep and eventually fill with sediment. In acidic conditions, a kettle bog may form but in alkaline conditions, it will be kettle peatland . Kettles are fluvioglacial landforms occurring as

315-664: The University of Copenhagen instead uses the unambiguous "b2k", for "years before 2000 AD", often in combination with the Greenland Ice Core Chronology 2005 (GICC05) time scale. Some authors who use the YBP dating format also use "YAP" ("years after present") to denote years after 1950. SI prefix multipliers may be used to express larger periods of time, e.g. ka BP (thousand years BP), Ma BP (million years BP) and many others . Radiocarbon dating

350-448: The carbon isotopes in the atmosphere, which scientists must account for. In a convention that is not always observed, many sources restrict the use of BP dates to those produced with radiocarbon dating; the alternative notation "RCYBP" stands for the explicit "radio carbon years before present". The BP scale is sometimes used for dates established by means other than radiocarbon dating, such as stratigraphy . This usage differs from

385-533: The Cordilleran Ice Sheet is called the Puget Lobe. During the Vashon Glaciation, the Cordilleran Ice Sheet grew and advanced southwards at a rate of about 135 metres (443 ft) per year. The Vashon Glaciation actually began after the planet's Last Glacial Maximum . Glaciers were retreating throughout most of the world, but growing in Western Washington. Around 18,350 BP, the Puget Lobe blocked

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420-819: The North American ice sheet complex, which covered present day Canada and much of the northern U.S . This cold glaciated time for North America was called the Wisconsin glaciation . During the Vashon glaciation, the climate in Western Washington , like most places, was much colder than today. As well as being cold, it was also much drier than in current times, which was characteristic of some places, and opposite of others. Pollen data collected from Battleground Lake in southwest Washington (state) shows that from 20,000 – 16,000 BP, annual temperatures in

455-403: The Puget Lobe receded, blocks of ice broke off and became separate. The melting glacier produced streams which carried sediment. The bottom of the ice blocks became buried in sediment. As the blocks of ice melted, it left depressions in the ground called kettles . Some of these kettles filled up with water to become kettle lakes and kettle ponds. (see Kettle (landform) ) Glacial Lake Carbon

490-517: The Puget Sound from reaching the Strait of Juan de Fuca, turning the Puget Sound into Glacial Lake Russell . By around 17,950 BP, the glacier reached present-day Seattle. By around 17,650 BP, the Puget Lobe reached present-day Tacoma. By around 17,350 BP, the glacier reached present-day Olympia. The Puget Lobe reached its maximum extent in the vicinity of the present-day city of Tenino around 16,950 BP. The Puget Lobe remained at its maximum extent in

525-433: The area were about 6 ± 1 °C (10.8 ± 1.8 °F) colder than in present times (present times as of 1990), and precipitation was around 1 meter (39.4 inches) less. The Battle Ground area averaged 52.14 inches (132.44 cm) of precipitation per year for the period of 1961–1990. A meter less precipitation means that during period of 20,000 – 16,000 BP, the average precipitation would have only been around 24.5% of what it

560-513: The area were around 2 ± 1 °C (3.6 ± 1.8 °F) warmer than present with 45 ± 5% less precipitation. Between 9,500 and 5,000 BP, there was Alnus (alder), Pseudotsuga (Douglas fir), Pteridium (bracken fern), and high amounts of Chrysolepis (chinkapin) and Quercus (oak trees). Before Present Before Present ( BP ) or " years before present ( YBP )" is a time scale used mainly in archaeology , geology, and other scientific disciplines to specify when events occurred relative to

595-508: The block was buried by sediment. Most kettle holes are less than two kilometres in diameter, although some in the U.S. Midwest exceed ten kilometres. Puslinch Lake in Ontario, Canada, is the largest kettle lake in Canada spanning 160 hectares (400 acres). Fish Lake in the north-central Cascade Mountains of the U.S. state of Washington is 200 hectares (490 acres). The depth of most kettles

630-476: The exponential decay relation and the "Libby half-life" 5568 a. The ages are expressed in years before present (BP) where "present" is defined as AD 1950. The year 1950 was chosen because it was the standard astronomical epoch at that time. It also marked the publication of the first radiocarbon dates in December 1949, and 1950 also antedates large-scale atmospheric testing of nuclear weapons , which altered

665-447: The glacier only came down to present-day Olympia. The Puget Lobe began to uncover Glacial Lake Russell. By 16,450 BP, the Puget Lobe only came down to Tacoma. By 16,150 BP, the glacier only came down to Seattle. By about 16,000 BP, the Puget Lobe retreated far enough north that Glacial Lake Russell and the Strait of Juan de Fuca became connected, making Glacial Lake Russell the salt water body of Puget Sound again. For areas on land, as

700-480: The global ratio of carbon-14 to carbon-12 . Dates determined using radiocarbon dating come as two kinds: uncalibrated (also called Libby or raw ) and calibrated (also called Cambridge ) dates. Uncalibrated radiocarbon dates should be clearly noted as such by "uncalibrated years BP", because they are not identical to calendar dates. This has to do with the fact that the level of atmospheric radiocarbon ( carbon-14 or C) has not been strictly constant during

735-595: The groundwater table will usually become dry during the warm summer months, in which case they are deemed ephemeral . If water in a kettle becomes acidic due to decomposing organic plant matter, it becomes a kettle bog ; or, if underlying soils are lime -based and neutralize the acidic conditions somewhat, it becomes a kettle peatland . Kettle bogs are closed ecosystems because they have no water source other than precipitation. Acidic kettle bogs and fresh water kettles are important ecological niches for some symbiotic species of flora and fauna. The Kettle Moraine ,

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770-415: The melting blocks of sediment-rich ice that were transported and consequently buried by the jökulhlaups. It was found in field observations and laboratory simulations done by Maizels in 1992 that ramparts form around the edge of kettle holes generated by jökulhlaups. The development of distinct types of ramparts depends on the concentration of rock fragments contained in the melted ice block and on how deeply

805-516: The name (standard codes are used) of the laboratory concerned, and other information such as confidence levels, because of differences between the methods used by different laboratories and changes in calibrating methods. Conversion from Gregorian calendar years to Before Present years is by starting with the 1950-01-01 epoch of the Gregorian calendar and increasing the BP year count with each year into

840-416: The origin of practical radiocarbon dating in the 1950s. Because the "present" time changes, standard practice is to use 1 January 1950 as the commencement date (epoch) of the age scale, with 1950 being labelled as the "standard year". The abbreviation "BP" has been interpreted retrospectively as "Before Physics", which refers to the time before nuclear weapons testing artificially altered the proportion of

875-399: The past from that Gregorian date. For example, 1000 BP corresponds to 950 AD, 1949 BP corresponds to 1 AD, 1950 BP corresponds to 1 BC, 2000 BP corresponds to 51 BC. Kettle (landform) A kettle (also known as a kettle hole , kettlehole , or pothole ) is a depression or hole in an outwash plain formed by retreating glaciers or draining floodwaters . The kettles are formed as

910-496: The recommendation by van der Plicht & Hogg, followed by the Quaternary Science Reviews , both of which requested that publications should use the unit "a" (for "annum", Latin for "year") and reserve the term "BP" for radiocarbon estimations. Some archaeologists use the lowercase letters bp , bc and ad as terminology for uncalibrated dates for these eras. The Centre for Ice and Climate at

945-424: The result of blocks of ice calving from the front of a receding glacier and becoming partially to wholly buried by glacial outwash. Glacial outwash is generated when streams of meltwater flow away from the glacier and deposit sediment to form broad outwash plains called sandurs . When the ice blocks melt, kettle holes are left in the sandur. When the development of numerous kettle holes disrupt sandur surfaces,

980-596: The span of time that can be radiocarbon-dated. Uncalibrated radiocarbon ages can be converted to calendar dates by calibration curves based on comparison of raw radiocarbon dates of samples independently dated by other methods, such as dendrochronology (dating based on tree growth-rings) and stratigraphy (dating based on sediment layers in mud or sedimentary rock). Such calibrated dates are expressed as cal BP, where "cal" indicates "calibrated years", or "calendar years", before 1950. Many scholarly and scientific journals require that published calibrated results be accompanied by

1015-570: The vicinity of present-day Tenino from around 16,950 BP to around 16,850 BP, a total of about 100 years. The ice depths were about 1.6 kilometres (0.99 mi) at the present-day Canada–United States border, 1,000 metres (3,300 ft) in Seattle, and 200 metres (660 ft) at the glacier's terminus in the Tenino area. Around 16,850 BP, the Puget Lobe began retreating northward at a rate of about 340 meters (1,120 feet) per year. By about 16,650 BP,

1050-772: Was a lake created by the Puget Lobe damming the Carbon River. Around 16,850 BP when the glacier began retreating, the ice dam holding back the lake became breached causing a major glacial outburst flood. The flood covered present day central and northern Thurston County, part of Pierce County, and small parts of Lewis and Grays Harbor Counties. Bison antiquus Panthera atrox Smilodon fatalis Thomomys mazama melanops Abies lasiocarpa Picea engelmannii Artemisia Pollen data collected from Battleground Lake shows that between 16,000 and 15,000 BP, temperatures were around 4 ± 2 °C (7.2 ± 3.6 °F) colder than present (present as of 1990). The amount of precipitation

1085-446: Was first used in 1949. Beginning in 1954, metrologists established 1950 as the origin year for the BP scale for use with radiocarbon dating, using a 1950-based reference sample of oxalic acid . According to scientist A. Currie Lloyd: The problem was tackled by the international radiocarbon community in the late 1950s, in cooperation with the U.S. National Bureau of Standards . A large quantity of contemporary oxalic acid dihydrate

Vashon Glaciation - Misplaced Pages Continue

1120-588: Was in the near present 1961–1990 period. The Laurentide Ice Sheet had a major effect on the climate. It was an ice sheet covering much of Canada, and parts of the northern United States in the Midwest and east. The Rocky Mountains separated the Laurentide Ice Sheet from the Cordilleran Ice Sheet. The Laurentide Ice Sheet had a cooling effect on the middle latitudes. This caused the jet stream over North America to split in two. The southern branch

1155-525: Was prepared as NBS Standard Reference Material (SRM) 4990B. Its C concentration was about 5% above what was believed to be the natural level, so the standard for radiocarbon dating was defined as 0.95 times the C concentration of this material, adjusted to a C reference value of −19 per mil (PDB). This value is defined as "modern carbon" referenced to AD 1950. Radiocarbon measurements are compared to this modern carbon value, and expressed as "fraction of modern" (fM). "Radiocarbon ages" are calculated from fM using

1190-505: Was pushed further south than it is in present times meaning that the storm tracks were missing the Pacific Northwest most of the time. Because of this, Southern and Central California had wetter climates than in present times. Average annual temperatures in the lowlands of Western Washington were above 0 °C (32 °F). This means that there was more summer thawing than there was winter freezing. This would seem to be

1225-477: Was similar to that of the present. From about 14,000 to 12,000 BP, more Pinus contorta (lodgepole pine) began to grow in the region, but was still an open area. Currently, the earliest human beings known to be in Western Washington were present as of 13,800 BP. A mastodon kill site from that time period was excavated in Sequim in 1977. From 12,000 BP to 10,000 BP, the area got a wider variety of trees, and became

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