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The 6th great lake, Lake Agassiz, was larger than all the others combined

[July 17, 2023: Staff Writer, The Brighter Side of News]

Where the Lake Agassiz waters went over time. (CREDIT: Sheffield University)

The five Great Lakes, specifically Huron, Ontario, Michigan, Erie, and Superior, stand as prominent features of North America. These vast expanses of water serve as common boundaries for several U.S. states and Canada. Yet, there was a time when these Great Lakes were overshadowed by an even more colossal body of water: Lake Agassiz.

Of the present-day Great Lakes, Lake Superior holds the distinction of being the largest, boasting a remarkable span of 31,699 square miles. Lakes Michigan and Huron, often regarded as one due to their interconnectedness, collectively encompass an area of 45,300 square miles. Together, these enormous bodies of water form the largest system of freshwater globally, accounting for an awe-inspiring 21% of the world's freshwater resources.


Though Lake Agassiz no longer exists, it once stood as one of North America's most immense lakes during the last glacial period, boasting an estimated expanse of around 170,000 square miles. This prehistoric behemoth, in existence over 10,000 years ago, significantly influenced the development of the continent's topography and climate.

This ancient lake, christened after Louis Agassiz, a Swiss-American naturalist who was the initial proponent of its existence in the mid-19th century, sprawled over large swathes of what is now recognized as central Canada and the northern United States. The basin of Lake Agassiz stretched from the western boundaries of the Rocky Mountains to the eastern fringes of the Appalachians, and from the northern rim of the Arctic Ocean to the southern shores of the Gulf of Mexico.


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The origin of Lake Agassiz is thought to have been prompted by the withdrawal of the Laurentide Ice Sheet, which blanketed a significant portion of North America during the last ice age. As the ice sheet thawed, it generated colossal volumes of meltwater that streamed into the continent's low-lying regions, ultimately leading to the formation of a series of massive lakes, one of which was Lake Agassiz.

With the passage of time, Lake Agassiz swelled to a remarkable size, with depths exceeding 700 feet in some places. It was replenished by a plethora of rivers and streams, such as the Red River of the North, the Minnesota River, and the Winnipeg River. At its zenith, its water content surpassed the combined volume of the present-day Great Lakes.


The vast size of Lake Agassiz had a significant impact on the climate and ecology of North America. Its presence modified the prevailing wind patterns, creating a more humid environment in the surrounding areas. It also affected the distribution of plant and animal species, as well as the migration patterns of early human populations.

Long before the Great Lakes existed, there was a massive lake that dwarfed them all in size: Lake Agassiz. (CREDIT: Creative Commons)

One of the most significant events associated with Lake Agassiz was the catastrophic flooding that occurred when its ice dam broke. The ice dam, which formed at the southern end of the lake, was created by the accumulation of glacial ice that prevented the lake from flowing into the Mississippi River.

As the water level in Lake Agassiz rose, the pressure on the ice dam increased. Eventually, the dam gave way, releasing a massive flood that swept across the northern United States and Canada. The floodwaters carved deep channels in the landscape, creating features such as the Grand Coulee and the Columbia River Gorge.


The effects of the Lake Agassiz flood were felt as far south as the Gulf of Mexico, where sediment deposits from the flood were found. The floodwaters also altered the course of several major rivers, including the Missouri and the Mississippi.

Today, Lake Agassiz is no longer visible on the landscape, as it drained completely after the last ice age. However, its legacy can still be seen in the features it left behind, including the Red River Valley and the many lakes and wetlands that dot the region.

Due to the Laurentide Ice Sheet causing a dam effect, Lake Agassiz formed from the glacial melt and rivers. (CREDIT:

Scientists continue to study the history and impact of Lake Agassiz, using a range of tools and techniques to understand this prehistoric giant. One of the most significant recent discoveries has been the use of sediment cores from the lake bed, which provide a detailed record of its history and the environmental conditions of the time.


These sediment cores have revealed a wealth of information about the climate and ecology of North America during the last ice age, as well as the changes that occurred as the ice sheet retreated and the lake drained. They have also provided insights into the evolution of plant and animal species, as well as the movements of early human populations.

As the ice sheet shifted, it caused changes in Lake Agassiz, making it overflow and fade away. (CREDIT: iStock)

The study of Lake Agassiz has also shed light on the broader field of paleoclimatology, which seeks to understand past climate patterns and their impact on the planet. By studying the climate of the past, scientists hope to gain a better understanding of the current and future changes that are occurring, as well as a result of human activity.

One of the key findings from the study of Lake Agassiz is that the climate of North America during the last ice age was much more variable than previously thought. While the prevailing view was that the region was uniformly cold and dry, the sediment cores from Lake Agassiz suggest that there were significant fluctuations in temperature and precipitation.


These fluctuations are thought to have been driven by a range of factors, including changes in ocean circulation, solar activity, and atmospheric circulation patterns. Understanding these factors and their impact on the climate of the past can help scientists better predict and prepare for future climate change.

Lake Erie today (CREDIT: Shutterstock)

Another important aspect of the study of Lake Agassiz is its relevance to Indigenous communities in the region. For many Indigenous peoples, the lake and its surroundings hold significant cultural and spiritual importance. The study of the lake's history and impact can help to deepen our understanding of Indigenous knowledge and perspectives, and to support Indigenous-led research and management of the region.


In recent years, there have been efforts to incorporate Indigenous perspectives and knowledge into the study of Lake Agassiz and its legacy. For example, the University of Manitoba's Centre for Earth Observation Science has partnered with Indigenous communities in the region to develop a shared understanding of the lake's history and significance.

These efforts have also highlighted the need for greater collaboration and engagement between Indigenous and non-Indigenous researchers and stakeholders. By working together, we can gain a more comprehensive and inclusive understanding of the past and present of the region, and work towards a more sustainable and equitable future.

The legacy of Lake Agassiz extends beyond the fields of science and culture, and has important implications for policy and management in the region. The many lakes and wetlands that were formed as a result of the lake's drainage provide important ecosystem services, including water filtration, carbon sequestration, and wildlife habitat.

However, these ecosystems are facing a range of threats, including habitat loss and fragmentation, pollution, and climate change. To protect and restore these ecosystems, there is a need for coordinated and integrated management approaches that take into account the multiple social, economic, and environmental values at stake.

In recent years, there have been efforts to develop such approaches, including the Lake Winnipeg Basin Initiative, a collaborative effort to improve the health and resilience of the lake and its watershed. The initiative brings together Indigenous and non-Indigenous stakeholders from across the region to develop and implement a shared vision for the future of the basin.


Efforts such as these demonstrate the potential for collaborative and integrated approaches to environmental management, and highlight the importance of recognizing and respecting the multiple perspectives and values at play in complex environmental issues.

Lake Agassiz may be a prehistoric giant, but its legacy continues to shape the landscape and people of North America. By studying its history and impact, we can gain a better understanding of the complex and interconnected systems that shape our planet, and work towards a more sustainable and equitable future for all.

For more science stories check out our New Discoveries section at The Brighter Side of News.


Note: Materials provided above by the The Brighter Side of News. Content may be edited for style and length.


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