The Fraser Glaciation lasted
for about 10,000 years. The ice
that entered the Puget Sound occurred during the Pleistocene era.
The glacial occupation of the Puget Sound region is called the Puget
Sound Lobe. The advance began in the Olympic Mountains and was the
beginning of the first stade: the Evans Creek Stade. At that time the ice
divided going into the Strait of Juan de Fuca and Puget Sound. The next stade was the Vashon stade, which reached its peak
15,000 years ago. This stage was much shorter and ended around 13,500 years ago.
To view the Glacial and Interglacial cycle view this link: http://www.nps.gov/olym/glacier/glaciate.htm
The maximum extent of this stage was reached at about 21000-19000 years
B.P. (before present). The glacier
may have extended at its fullest to the Puget Sound Lowlands.
The Evans Creek Stade produced protracted alpine glaciation. This type of glaciation is where the ice was formed in the
Cascade and Olympic Mountain Ranges, which formed glaciers in the valleys.
This Stage of Fraser Glaciation began in British Columbia and spread
towards the area we now know as Issaquah near Snoqualmie Pass.
In the Issaquah area the glacier is thought to have reached a maximum
thickness of about 3,000 feet! As
the Vashon Glacier retreated there were five main stages of ice stagnation that
formed the topography (surface features) that exists today.
Five main stages of this retreat were (from oldest to youngest):
1. The glacier still occupied
present day Lake Sammamish and as it melted drainage took place through Issaquah
Creek and Tibbetts Creek.
Lake Sammamish was formed and melting from Issaquah Creek was deposited
into the newly formed lake. Drainage
out of the lake went through Tibbetts Creek.
A large delta formed in the North Fork of Issaquah Creek and drainage out
of Lake Sammamish occurred through what is now I-90.
Formation of the edges of the lake were happening along the eastern
Lake was much larger than its present size and occupied all of the lower
A low delta formed from 100-150 feet above sea level just south of
present day Issaquah
Species are those which are unique to a particular area and are not found
anywhere else in the world. The
Fraser Glaciation had a large impact on plants and animals in limiting their
habitat ranges with its glacial advance. Most
of the affected endemic species are found only on the Olympic Peninsula and in
the Olympic Mountain Range.
Mountain milkvetch Astragalus
australis var. olympicus
bellflower Campanula piperi
fleabane Erigeron flettii
wandering fleabane Erigeron peregrinus peregrinus var. thompsonii
rock spirea Petrophytum hendersonii
Mountain Groundsel Senecio neowebsteri
Mountain synthyris Synthyris pinnatifida var. lanuginosa
violet Viola flettii
Marmot Marmota olympus
yellow-pine chipmunk Tamias amoenus caurinus
snow mole Scapanus townsendii olympicus
Mazams pocket gopher Thomomys mazama melanops
ermine Mustela erminea olympica
torrent salamander Rhyacotriton olympicus
mudminnow Novumbra hubbsi
rainbow trout Oncorhynchus mykiss irideus
cutthroat trout Oncorhynchus clarki clarki
skipper Hesperia comma hulbirti
grasshopper Nisquallia olympica
gazelle beetle Nebria danmanni
gazelle beetle Nebria acuta quileute
beetle Cicindela bellissima frechini
slug Hemphillia dromedarius
jumping slug Hemphillia burringtoni
The species of particular interest to the Vashon Stade of the Fraser
Glaciation is the Olympic Mudminnow (Novumbra hubbsi).
The Olympic Mudminnow reaches a maximum length of only 8 cm.
Today there are only four species of the Mudminnow in existence.
There are two found in the Eastern US, 1 in Central Europe and 1 that
exists in the area once covered by the Vashon Glacier.
The possible reasons that the Olympic Mudminnow has such a limited
distribution are mainly due to glaciation.
During the Fraser Glaciation the Vashon Glacier all of the river systems
became non-existent. After the
retreat of the ice sheet the Mudminnow had developed specialized behavioral
preferences it was unable to leave its limited habitat range.
Fraser Glaciation lasted about 10,000 years, a short time based on the history
of the Earth. In this relatively
short time period, the cycle of glaciation has resulted in the formation of many
of the large lakes in the Pacific Northwest.
Also, it limited the habitat range of a number of species of plants and
animals giving this region the privilege of being the home to a number of