Vashon Glaciation
| Vashon Glaciation | |
| 20,000 - 15,000 BP (18,050 - 13,050 BCE) | |
| Location | |
| Continent: | North America |
|---|---|
| Present-day country: | United States of America |
| Present-day state: | Washington |
| Region: | Western Washington |
| Geologic Time Scale | |
| Eon: | Phanerozoic |
| Era: | Cenozoic |
| Period: | Quaternary |
| Epoch: | Pleistocene |
| Age: | Upper Pleistocene |
| Other time periods | |
| Ice age: | Quaternary glaciation (current ice age) |
| Glacial period: | Last glacial period |
| Human history: | Paleolithic |
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.[1] It lasted from about 20,000 - 15,000 BP (18,050 - 13,050 BCE).[2] 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.[3][4] It crossed the present-day Canada–United States border around 19,000 BP (17,050 BCE).[4] The glacier reached its maximum extent in the vicinity of the present-day city of Tenino[5] around 16,950 BP (15,000 BCE).[3]
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.[3] 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.[3]
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.[6] The low precipitation was caused by the Laurentide Ice Sheet,[6] 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.[6] The southern branch was pushed further south than it is in present times.[6] The winter storm tracks instead were hitting places further south, thus missing present-day Washington State most of the time.[6] Because of this, Southern and Central California had wetter climates than in present times.[7]
The Retreat
The Retreat
After around 16,900 BP (14,950 BCE), the Cordilleran Ice Sheet began retreating northward at a rate of about 340 meters (1,120 feet) per year.[3]
Formation of the new Puget Sound
The retreating glacier uncovered the low-lying areas where the Puget Sound was prior to the Vashon Glaciation.[4] The water from the melting ice filled in these low-lying areas recreating the Puget Sound.[4] By about 16,000 BP (14,050 BCE), the glacier retreated far enough north that the Puget Sound and the Pacific Ocean became connected, just like it was for a brief period of time before the Vashon Glaciation.[4] This allowed Puget Sound to become a salt water body.[4]
Formation of Kettle Lakes
For areas on land, as the glacier 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))
Climate
After about 16,000 BP (14,050 BCE), the climate began to warm. From about 16,000 BP (14,050 BCE) to around 15,000 BP (13,050 BCE), temperatures were only 2-6 °C (4-11 °F) colder than in present times (present-times as of 1990).[6] Annual precipitation increased to about what it is in present-times (1990).[6]
Plant Species
| Plant Name (scientific) | Plant Name (common) | Location | Time Period |
|---|---|---|---|
| Abies lasiocarpa[6] | Subalpine Fir[6] | Puget Sound region[6] | 21,000 - 17,000 BP (19,050 – 15,050 BCE)[6] |
| Alnus[6] | Alder[6] | Olympic Peninsula (West side lowlands)[6] | 20,000 - 16,000 BP (18,050 – 14,050 BCE)[6] |
| Artemisia[6] | Sagebrush or Wormwood[6] | Puget Sound region, Olympic Peninsula (west side, near the alpine glaciers)[6] | 20,000 - 16,000 BP (18,050 – 14,050 BCE)[6] |
| Cyperaceae[6] | Sedge[6] | Puget Sound region[6] | 20,000 - 16,000 BP (18,050 – 14,050 BCE)[6] |
| Picea[6] | Spruce[6] | Puget Sound region, Olympic Peninsula (west side lowlands)[6] | 20,000 - 16,000 BP (18,050 – 14,050 BCE)[6] |
| Picea engelmannii[6] | Engelman Spruce[6] | Puget Sound region[6] | 21,000 - 17,000 BP (19,050 – 15,050 BCE)[6] |
| Pinus[6] | Pine[6] | Puget Sound region, Olympic Peninsula (west side lowlands)[6] | 20,000 - 16,000 BP (18,050 – 14,050 BCE)[6] |
| Pinus contorta[6] | Lodgepole Pine[6] | Puget Sound region[6] | 21,000 - 17,000 BP (19,050 – 15,050 BCE)[6] |
| Poaceae[6] | True Grasses | Puget Sound region, Olympic Peninsula (west side, near the alpine glaciers)[6] | 20,000 - 16,000 BP (18,050 – 14,050 BCE)[6] |
| Taxus brevifolia[6] | Pacific Yew[6] | Puget Sound region[6] | 21,000 - 17,000 BP (19,050 – 15,050 BCE)[6] |
| Tsuga heterophylla[6] | Western Hemlock[6] | Olympic Peninsula (west side lowlands)[6] | 20,000 - 16,000 BP (18,050 – 14,050 BCE)[6] |
| Tsuga mertensiana[6] | Mountain Hemlock[6] | Olympic Peninsula (west side lowlands)[6] | 20,000 - 16,000 BP (18,050 – 14,050 BCE)[6] |
Animal Species
| Animal Name (scientific) | Animal Name (common) | Time Period |
|---|---|---|
| Mammuthus columbi | Columbian Mammoth | 16,000 BP (14,050 BCE)[8] |
References
- ↑ 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.
- ↑ 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
- 1 2 3 4 5 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
- 1 2 3 4 5 6 http://www.youtube.com/watch?v=YHWMHzi_deg Vashon Glaciation Animation
- ↑ 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
- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 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
- ↑ 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
- ↑ http://www.cbsnews.com/news/scientists-hope-to-lift-mammoth-tusk-from-trench-in-seattle/ Scientists hope to lift mammoth tusk from construction site in Seattle