GLACIATION OF NORTH AMERICA more  -->

The world was a much different place 14,000 years ago. Global temperatures were significantly colder than they are today, with northern oceans an average of 4 to 8 degrees colder than modern temperatures. Huge stretches of ice covered most of northern Europe and all but the southern tip of the British Isles. In North America, two large ice sheets covered most of Canada during their largest stages, what geologists and archaeologists call the Last Glacial Maxim or LGM for short. Sea levels were also dramatically different during the LGM due to the twin pressures of eustacy and isostacy. During periods of glaciation, precipitation becomes trapped in glaciers, preventing it from replenishing the Earth’s oceans. This results in a eustatic drop in sea levels. Isostatic sea level change results not from trapped water but from the effects of ice weighing down on the Earth’s crust.

GLACIATION

glacier is a large, slow-moving mass of ice and compact snow. Today, glaciers are found only in the polar regions and in high mountainous areas; however, in the past, they covered vast areas of the Earth's surface and shaped much of the landscape that we see today. During the Pleistocene Epoch (a geologic time period from 1.8 million years ago to 10,000 years ago), cycles of glacial expansion and retreat occurred repeatedly. These cycles are composed of both glacial periods in which the climate cools and glaciers grow, and interglacial periods where the warming climate causes ice bodies to recede.

The last glacial period in North America is called the Wisconsinan Glaciation, which is divided into the Early (80,000 to 55,000 years ago) and Late (25,000 to 10,000 years ago) glacial stages with an interglacial stage between 55,000 to 25,000 years ago. During the Late Wisconsinan glacial stage, most of Canada and parts of the northern United States were covered by two massive ice sheets, the Cordilleran, which lay to the west of the Rocky Mountains, and the Laurentide to the east. An ice sheet is formed through the convergence of several glaciers, and is the largest of all ice bodies. These ice sheets are estimated to have had a maximum thickness of 2 to 4 km.

Studies of glacial deposits suggest that a large part of the two ice sheets were joined together above central Alberta, near Edmonton, until long after the glacial maximum. Geologists use glacial deposits such as moraine (a landform made up of rocks and sediments that have been transported and deposited by a glacier) and till (unsorted sediments ranging in size from clays to boulders that have been carried and deposited by glacial ice) in addition to the rubble caught up and deposited by glaciers to demonstrate the furthest extent of the sheets. 

GLACIATION AND SEA LEVEL CHANGE

A major consequence of glaciation is its effect on sea levels. Several factors related to glaciation can influence sea levels on either a global or a local scale including eustatic and isostatic changes as well as tectonic factors.

Eustatic Sea Level Change

Eustatic sea level change is a global adjustment in the total volume of sea water contained within the oceans' basins. Under normal climatic conditions, water evaporates from the oceans and is transported and deposited over the Earth's land masses in some form of precipitation. Over time, this precipitation makes its way back to the oceans. This process is known as the hydrologic cycle. During periods of glaciation, precipitation becomes trapped in glaciers, preventing it from replenishing the Earth's oceans and results in a global, or eustatic, drop in sea levels.

Isostatic Sea Level Change

Isostatic sea level change is either the depression or uplift of the Earth's crust. Isostatic depression is caused by the loading of the Earth's crust in a localized area. During glacial periods, ice accumulates over a given area and its weight pushes down on the crust, causing the lowering of the land relative to sea level. Isostatic uplift or rebound is caused by a reduction of weight on a given area of the Earth's crust, resulting in the rebounding of the land.

Tectonic Factors

Sea level change caused by tectonic factors is the most geographically restricted of these three factors and occurs in seismically-active regions. Due to the mechanics of plate tectonics, stress builds along convergent or transverse plate margins until it is released through the slippage of one crust relative to the other along a fault line. This can result in either raised shorelines or drowned beaches.

ANCIENT COASTLINES

During the Last Glacial Maxim, the Pacific coast of North America was very different than today's coastline.  Much of the earth's water was trapped in glacial ice and global sea levels were between 100 to 150 m lower than they are today. Large stretches of coastal land emerged from the ocean floor off the coast of the Pacific Northwest. As the glaciers melted and sea levels rose, the ancient coastline was drowned, along with any archaeological evidence that early people may have left behind. In order for archaeologists to find this evidence, they must first look for the ancient coastline.

The identification of ancient coastlines is a complicated process. Although sea levels were generally lower during the Ice Age, in some areas of the Pacific northwest coast they were actually higher than today. This is due to isostatic depression, which occurs when the weight of glacial ice pushes the land downward, causing relative sea levels to rise. When the ice melts, the land rebounds upward. While many ancient coastal sites may be drowned beneath metres of ocean water today, others may be stranded far inland in dense coastal rainforest. In order to overcome these difficulties, geologists have created detailed localized sea level charts for many areas of the coast, and this data is used to reconstruct the ancient shorelines. Remote sensing of the sea floor off Haida Gwaii has led to the identification of ancient riverbeds and forest floors, providing more clues as to the possible location of archaeological sites.

Investigation of Ancient Coastlines

Investigating these ancient coastlines can be incredibly difficult - reconstructions place the depth of some of the river drainages and ancient terraces to 50 m below the modern ocean and the cold water can make underwater excavation extremely challenging. However, archaeologists have developed special tools called "grabbers" to pull up material from the ocean floor. In some places, they have found ancient tree stumps, proving that the land was once above the sea.

Prior to 1994 when this website was created, a tantalizing glimpse of what may lay just below the ancient riverbeds was also uncovered. Using reconstructed maps of the paleoenvironmental (ancient) landscape, Daryl Fedje and a team of archaeologists from the Canadian National Parks Service dropped a bucket over 50 m from the deck of a Coast Guard vessel. When the bucket was retrieved, the team meticulously screened (sifted or searched through) the collected soil sediment from the ocean bed, uncovering a single, unmistakable artifact - a slate blade. Though this was a test, the retrieval of a slate blade from 50 m below the surface demonstrates that humans were occupying these ancient exposed coastlines.

GLACIAL LANDFORMS

Glaciers are responsible for many of the topographic features we see in the landscape today including the foothills erratics train, eskers and kame terrraces.

Foothills Erratics Train

Erratics are large boulders that have been transported and deposited by glaciers. In southern Alberta, along the eastern side of the Rocky Mountains, thousands of erratics form a train over 600 km long! When geologists examined them, they discovered that they were all made of the same material, which was sourced to an area around Mount Edith Cavell in Jasper Park. Thousands of years ago, these large boulders fell onto the surface of the Cordilleran ice sheet and were slowly carried outward onto the Plains. When the ice melted, the long train of boulders was left behind. They contain clues that have helped scientists to understand the movements of the ice sheets that covered Canada during the Late Wisconsinan glacial stage. The path of the erratics takes a sharp right-angle turn out on the Plains, changing from an easterly to a southerly direction. Scientists believe that the western Cordilleran ice sheet, which was carrying the erratics, met the eastern Laurentide ice sheet and was deflected south.

Eskers

Eskers are long, curved ridges that develop beneath an ice sheet and are formed from gravel, sand and other sediments that have been deposited by glacial meltwater. Eskers range in height from a few metres to tens of metres and in length from a few metres to hundreds of kilometres. They are very common in northern Canada and were also important dry transportation routes for animals and people in the early post-glacial period.

Kame Terraces

Kame terraces are narrow, raised ridges of land found along the sides of glacial valleys. These features are formed by the deposition (buildup) of sand, gravel and other sediments between a melting glacier and an adjacent valley wall. Today, kame terraces are an important economic resource because the gravel they contain can be extracted for use in road building and concrete. However, in the past, they were prime sites for human habitation due to their elevation above the surrounding landscape. The McCallum archaeological site in the Fraser Valley (British Columbia) is situated on a kame terrace, which formed between the melting ice and the valley wall. As the sediment, gravel and sand built up, the ice melted away, leaving a flat surface that is elevated above the lower ground where the glacier formerly sat.

COASTAL REFUGIA

The Cordilleran ice sheet blanketed British Columbia during the Ice Age and was long thought to have reached all the way across the outer coast to the Pacific Ocean. However, ancient plant and animal remains found on several offshore islands off the Pacific coast from Alaska to southern British Columbia provide evidence that some areas of land on the outer coast remained unglaciated and habitable during the Ice Age. These ice-free areas are called refugia.

Cape Ball

Research at a sea cliff at Cape Ball, on eastern Graham Island off the Pacific coast of British Columbia, has provided evidence that this coastal region remained ice-free throughout the Late Wisconsinan glaciation. Graham Island is part of the Queen Charlotte Island group (now called Haida Gwaii), and for many years researchers believed that the islands were completely buried under glacial ice during the Late Wisconsinan. However, the discovery of ancient plant fossils at Cape Ball confirmed that the environment was in fact habitable, and supported a diverse array of plant life.

On Your Knees Cave

On Your Knees Cave is an important paleontological and archaeological site located on Prince of Wales Island in the Alexander Archipelago off the coast of southeastern Alaska. The paleontological (fossilized animals and plants) evidence includes the fossil remains of both black and brown bears, which were dated to both before and after the last glaciation. Comparison of the DNA of modern bears with that of the fossilized remains has led researchers to conclude that brown bears have been inhabiting the islands continuously for 40,000 years, indicating that habitable refugia must have existed in this region throughout the last glaciation.

The archaeological evidence includes a bone tool, possibly an awl (long, pointed spike), which has been dated to 10,300±50 years BP, stone tools including microblades and bifaces, and human remains dating to about 9,200 years BP. Isotope analysis of the human bone indicated a marine-based diet. The stone tools were made of obsidian that was traced to a source on Mount Edziza in British Columbia. This evidence indicates that people were living on the island by 9,200 years BP, had established trade networks for obsidian, relied on marine resources for food and were almost certainly using some form of watercraft for travel between the islands of the archipelago and the mainland.

K-1 Cave

K-1 Cave is  located on Haida Gwaii (British Columbia). Archaeological evidence from sediments in K-1 Cave indicate that bears were present there by about 14,500 years BP, and salmon were present there by 12,000 years BP.

Port Eliza Cave

Port Eliza Cave is a raised sea cave located on the west coast of Vancouver Island, British Columbia. The plant and animal remains, including mountain goats, marmots and voles as well as several species of birds and fish, preserved in the cave have provided scientists with a unique window into the climate and environment of this coastal region between 16,000 and 18,000 years ago. 

The cave was formed at a time when relative sea levels were higher than present, and wave action eroded the cliff face and created the cave. When sea levels dropped, the cave became a dry inland shelter for animals living in the area.  Sometime after 16,000 years ago, glacial ice covered the mouth of the cave and fine-grained glacial sediments were deposited in the cave by melt water. These sediments buried the organic remains located on the cave floor. While there is no evidence for human use of this cave (no stone tools or material culture were found here), it demonstrates that this coastal region was habitable up until at least 16,000 years ago and capable of supporting a variety of life.