Glaciation | The Canadian Encyclopedia
Arthur S. Dyke. Geological Survey of Canada, Booth Street, Ottawa, Ontario, Canada, K1A 0E8 chiefly of improvements in radiocarbon dating with the advent of moraines and their names) and the Glacial Map of the. United States East. Date Published, February 7, Last Edited, December 16, A moraine is a landform composed of an accumulation of sediment deposited by or from a GLACIER and possessing a form independent of the terrain beneath it. Just after 13 14C a BP in central Canada, the retreating Ontario . High- resolution LiDAR mapping of glacial landforms and ice stream.
Lake Vermont - Wikipedia
This usually occurs at points where the bedrock is easily fractured, such as joints. They are large, asymmetrical, knob-like bedrock features with streamlined sides tapering up-glacier, and steep, abruptly broken sides down-glacier. In general, more erosion and removal of material takes place in valley glaciers, where the ice is confined by topography, than in the areas that are less constrained, such as ice caps and ice sheets.
Examples of features formed by valley glaciers include u-shaped valleys, such as the Bow Valley in the Rocky Mountains. This type of erosion deepened and widened pre-existing river valleys.
Depositional Features As erosion takes place in one area, deposition may occur in another. Deposition is the process in which glaciers add sand, minerals and other materials to the bedrock underneath. Forms such as drumlins and certain kinds of ground moraines can form under moving ice. However, most glacier deposition takes place as the ice retreats. Some examples of depositional features include: Most of these features contain a high percentage of glacial till, which is unstratified, unsorted material deposited directly from a glacier.
It usually consists of a heterogeneous mixture of claysilt, sand, pebbles, cobbles and boulders.
Till can be divided into several types depending on the location of debris in the ice and how it was deposited. Meltwater is another type of deposit left by glaciers. It can originate from the surface, inside or at the base of a glacier. These streams can become an interconnecting network of shallow channels that carry and deposit gravel and sand. Gravel is an important industrial resource in Canada, and some of the largest deposits have resulted from glacier-derived braided streams.
An excellent modern example is the Donjek River in Yukon. The Donjek Glacier in the Saint Elias mountain range fed this river. Kames short, knobby elevations and eskers sinuous ridges in rivers result from the deposition of sand and gravel by glacial streams.
- Last Glacial Period
- Glacial Lakes History
Lakes that were created from glacial deposits are found across Canada. The lakes were formed when the glacier either dammed the lake or left deposits that impeded draining. Lake Agassizwhich covers most of Manitoba and parts of Saskatchewan and Ontariois an outstanding example of a glacially dammed lake. Sediment in glacial lakes consists mostly of silt and clay.
These deposits will commonly form varves, which are coarse and fine layers of sediment that are deposited annually. The many raised beaches on both the north and south side of the lake give further evidence both of glacial rebound and of the different water levels which existed in the Great Lakes basin as the glaciers retreated. Raised Beach - Flat terraced areas show former lake levels called "raised beaches" image: From this time on the levels and shorelines of Lake Superior have been controlled by the elevation at the St Mary's rapids near Sault Ste Marie.
As this isostatic rebound continues to happen there will be more "raised beaches" formed on the north side of Lake Superior and more submerged beaches lost below the waves on the south shore. Glacial Moraines are large areas of sand, gravel and boulders left behind by the glaciers. A moraine represents the soils and rocks of Northern Ontario which were pushed ahead of the glaciers. They were left behind as raised glacial topography as the glaciers retreated.
From Moraines of northwestern Ontario modified from Sado and Carswell Climate Change and Lake Levels We know that the climate is changing rapidly today due to human caused pollution and land development.
We can also look back in history to see how different Lake Superior has been over the last thousands of years during natural climate variations. The passage below shows how trees can tell us how different the climate and lake levels were after the glaciers retreated: Lindquist became excited when his depth finder showed what appeared to be masts standing up off the bottom in feet of water. Gearing up with double tanks, he and his partner started down on their very deep dive with high expectations of dropping onto a shipwreck standing intact on the bottom.
The ice covered all land areas and extended into the ocean onto the middle and outer continental shelf. Irish geologists, geographers, and archaeologists refer to the Midlandian glaciation as its effects in Ireland are largely visible in the Irish Midlands.
Last Glacial Period - Wikipedia
Its deposits have been found overlying material from the preceding Ipswichian stage and lying beneath those from the following Holocenewhich is the stage we are living in today. This is sometimes called the Flandrian interglacial in Britain. Weichselian glaciation Scandinavia and northern Europe [ edit ] Main article: Weichselian glaciation Europe during the last glacial period Alternative names include: Weichsel glaciation or Vistulian glaciation referring to the Polish river Vistula or its German name Weichsel.
Evidence suggests that the ice sheets were at their maximum size for only a short period, between 25, and 13, BP. Eight interstadials have been recognized in the Weichselian, including: Initially, when the ice began melting about 10, BPseawater filled the isostatically depressed area, a temporary marine incursion that geologists dub the Yoldia Sea. Then, as post-glacial isostatic rebound lifted the region about BP, the deepest basin of the Baltic became a freshwater lake, in palaeological contexts referred to as Ancylus Lakewhich is identifiable in the freshwater fauna found in sediment cores.How do glaciers shape the landscape? Animation from geog.1 Kerboodle
The lake was filled by glacial runoff, but as worldwide sea level continued rising, saltwater again breached the sill about BP, forming a marine Littorina Sea which was followed by another freshwater phase before the present brackish marine system was established.
Thulin and Andrushaitis remarked when reviewing these sequences in Overlying ice had exerted pressure on the Earth's surface. This is important for archaeologists since a site that was coastal in the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore.
The Alps were where the first systematic scientific research on ice ages was conducted by Louis Agassiz at the beginning of the 19th century. Scandinavia and much of Britain were under ice. In the region of Bern it merged with the Aar glacier. The Rhine Glacier is currently the subject of the most detailed studies. Glaciers of the Reuss and the Limmat advanced sometimes as far as the Jura.
Beneath the surface, they had profound and lasting influence on geothermal heat and the patterns of deep groundwater flow.
The Pinedale lasted from approximately 30, to 10, years ago and was at its greatest extent between 23, and 21, years ago. USGS geologists estimate that the cycle of flooding and reformation of the lake lasted an average of 55 years and that the floods occurred approximately 40 times over the 2, year period between 15, and 13, years ago.
At the height of glaciation the Bering land bridge potentially permitted migration of mammals, including people, to North America from Siberia. It radically altered the geography of North America north of the Ohio River. In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hillswhich is the northernmost point in North America that remained south of the continental ice sheets.
The Great Lakes are the result of glacial scour and pooling of meltwater at the rim of the receding ice.