The Vashon Glaciation, Vashon Stadial or Vashon Stade is a local term for the most recent period of very cold climate in which during its peak, glaciers covered the entire
Salish Sea
, image = PNW-straits.jpg
, alt =
, caption = The Salish Sea, showing the open Pacific Ocean at lower left, and from there, heading inland: the Strait of Juan de Fuca, the narrow Puget Sound at lower ri ...
as well as present day
Seattle
Seattle ( ) is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest regio ...
,
Tacoma,
Olympia
The name Olympia may refer to:
Arts and entertainment Film
* ''Olympia'' (1938 film), by Leni Riefenstahl, documenting the Berlin-hosted Olympic Games
* ''Olympia'' (1998 film), about a Mexican soap opera star who pursues a career as an athlet ...
and other surrounding areas in the western part of present-day
Washington (state)
Washington (), officially the State of Washington, is a state in the Pacific Northwest region of the Western United States. Named for George Washington—the first U.S. president—the state was formed from the western part of the Washington ...
of the
United States of America
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territo ...
.
This occurred during a cold period around the world known as the
last glacial period. This was the most recent cold period of the
Quaternary glaciation
The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describe ...
, the time period in which the arctic ice sheets have existed. The Quaternary Glaciation is part of the
Late Cenozoic Ice Age
The Late Cenozoic Ice Age,National Academy of Sciences - The National Academies Press - Continental Glaciation through Geologic Times https://www.nap.edu/read/11798/chapter/8#80 or Antarctic Glaciation began 33.9 million years ago at the Eocen ...
, which began 33.9 million years ago and is ongoing. It is the time period in which the Antarctic ice cap has existed.
The Vashon Glaciation lasted from about 19,000 – 16,000
BP (
Before Present
Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Becaus ...
– present defined as January 1, 1950 for this scale). The
Cordilleran Ice Sheet was an ice sheet that covered present-day southern
Alaska
Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...
and parts of western
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
. The Fraser Glaciation began when the Cordilleran Ice Sheet advanced out of the mountains of British Columbia
[The cordilleran ice sheet - Accessed 2018-08-18 http://s46986.gridserver.com/resources/2004boothetal_Cordilleran.pdf] following the
Fraser River
The Fraser River is the longest river within British Columbia, Canada, rising at Fraser Pass near Blackrock Mountain in the Rocky Mountains and flowing for , into the Strait of Georgia just south of the City of Vancouver. The river's annual d ...
and
Fraser Valley
The Fraser Valley is a geographical region in southwestern British Columbia, Canada and northwestern Washington State. It starts just west of Hope in a narrow valley encompassing the Fraser River and ends at the Pacific Ocean stretching from the ...
. The Vashon Glaciation is an extension of the Fraser Glaciation in which the Cordilleran Ice Sheet advanced south of the present day
Canada–United States border
The border between Canada and the United States is the longest international border in the world. The terrestrial boundary (including boundaries in the Great Lakes, Atlantic, and Pacific coasts) is long. The land border has two sections: Can ...
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
The Laurentide Ice Sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and a large portion of the Northern United States, multiple times during the Quaternary glacial epochs, from 2.58 million years a ...
, Innuitian, and the currently existing
Greenland Ice Sheet
The Greenland ice sheet ( da, Grønlands indlandsis, kl, Sermersuaq) is a vast body of ice covering , roughly near 80% of the surface of Greenland. It is sometimes referred to as an ice cap, or under the term ''inland ice'', or its Danish equiva ...
all made up the North American ice sheet complex, which covered present day
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
and much of the northern
U.S
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. This cold glaciated time for
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
was called the
Wisconsin glaciation
The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cor ...
.
Climate (20,000 to 16,000 BP)
During the Vashon glaciation, the climate in
Western Washington
Western Washington is a region of the United States defined as the area of Washington state west of the Cascade Mountains. This region is home to the state's largest city, Seattle, the state capital, Olympia, and most of the state's residents. The ...
, 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 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 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
The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...
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 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
Southern may refer to:
Businesses
* China Southern Airlines, airline based in Guangzhou, China
* Southern Airways, defunct US airline
* Southern Air, air cargo transportation company based in Norwalk, Connecticut, US
* Southern Airways Express, M ...
and
Central California
Central California is generally thought of as the middle third of the state, north of Southern California, which includes Los Angeles, and south of Northern California, which includes San Francisco. It includes the northern portion of the San J ...
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 a climate too warm to support glaciers, but the ice was pushing in from the north faster than it could melt.
The advance (19,000 to 16,950 BP)
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 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 per year.
The Vashon Glaciation actually began after the planet's
Last Glacial Maximum
The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent.
Ice sheets covered much of Northern North America, Northern Eur ...
. Glaciers were retreating throughout most of the world, but growing in Western Washington. Around 18,350 BP, the Puget Lobe blocked the Puget Sound from reaching the Strait of Juan de Fuca,
turning the Puget Sound into
Glacial Lake Russell
During the Vashon Glaciation a series of lakes formed along the southern margin of the Cordilleran Ice Cap. In the Puget Sound depression, a series of lakes developed, of which Lake Russell was the largest and the longest lasting. Early Lake R ...
.
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 maximum extent (16,950 to 16,850 BP)
![Vashon Glaciation Map 2016-06-27](https://upload.wikimedia.org/wikipedia/commons/c/cd/Vashon_Glaciation_Map_2016-06-27.png)
The Puget Lobe remained at its maximum extent in 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 at the present-day Canada–United States border, in Seattle, and at the glacier's terminus in the Tenino area.
The retreat (16,850 to 16,000 BP)
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, 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.
;Formation of Kettles and Kettle Lakes
For areas on land, as 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)
A kettle (also known as a kettle lake, kettle hole, or pothole) is a depression/hole in an outwash plain formed by retreating glaciers or draining floodwaters. The kettles are formed as a result of blocks of dead ice left behind by retreating gla ...
)
;Glacial Lake Carbon – Catastrophic Glacial Outburst Flood
Glacial Lake Carbon 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.
Life during the Vashon Glaciation
Post Vashon Times (16,000 BP to present)
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 was similar to that of the present.
From about 14,000 to 12,000 BP, the area got more Pinus contorta (lodgepole pine), but was still an open area.
Currently, the earliest human beings known to be in Western Washington were there in 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 bigger variety of trees, and became 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
The Holocene Climate Optimum (HCO) was a warm period that occurred in the interval roughly 9,000 to 5,000 years ago BP, with a thermal maximum around 8000 years BP. It has also been known by many other names, such as Altithermal, Climatic Optimu ...
, temperatures in 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
''Chrysolepis'' is a small genus of plants in the family Fagaceae, endemic to the western United States. Its two species have the common name chinquapin. The genus occurs from western Washington south to the Transverse Ranges in Southern Califor ...
(chinkapin) and
Quercus
An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably '' ...
(oak trees).
Sequence of lakes
References
External links
Detailed Map of Vashon Glaciation - Washington State Department of Natural Resources
{{Continental Glaciations
Geology of Washington (state)
Ice ages
Natural history of Washington (state)
Glaciology of the United States