Deglaciation
Deglaciation refers to the process in which land surfaces previously covered by glacial ice are uncovered due to the melting or sublimation of ice. This phenomenon typically occurs at the end of a glacial stage, resulting in various environmental changes, including the formation of meltwater streams and lakes, rising global sea levels, and the ecological shifts in flora and fauna responding to the altered landscape. As glaciers melt, they transport and deposit sediment, leading to diverse geological features like glacially-covered sediment areas or bare bedrock.
Deglaciation is closely linked to climate change; it often follows periods of warming and can itself trigger additional warming through feedback mechanisms. For instance, melting glaciers decrease Earth's albedo, causing more solar energy to be absorbed, which further accelerates warming and glacier melt. The rapid nature of deglaciation can lead to significant ecological upheaval, including mass extinctions and shifts in animal migrations, while also creating unstable landscapes marked by high river gradients and potential for catastrophic lake drainage. Overall, deglaciation plays a critical role in shaping both the physical environment and climate systems.
Subject Terms
Deglaciation
Definition
Deglaciation is the uncovering or exposure of a land surface that was previously covered by glacial ice. It results from ice melting or subliming (transforming from solid directly into vapor). Deglaciation, therefore, accompanies the end of a glacial stage. As deglaciation occurs, several processes take effect. Among these processes are meltwater stream flow, development of meltwater lakes, addition of water to the world’s oceans (raising the global sea level), exposure of the land, and rebound of the land (lifting of the land’s elevation as a result of the removal of the weight of the overlying ice). In addition, faunal and floral changes accompany deglaciation in response to changes in landscape and ecology.
Glaciers have a seemingly infinite capacity to entrain and transport sedimentary material, from tiny clay particles to giant rock boulders. Glaciers move these materials within and upon the ice, but when they melt, sediment is deposited in the area where the ice melts. For this reason, areas that have experienced deglaciation are typically covered by glacially transported sediment. Alternatively, glaciers may sweep an area clean of loose material, creating deglaciated areas of bare bedrock. Where deglaciation has formed modern shorelines, those shorelines tend either to be laden with glacial sediment or to present bare bedrock to the waves. In some places, rebound has lifted the land along the modern shore, forming sea cliffs.
Deglaciation accompanies the transition from a glacial stage to an interglacial or warm stage. There have been several such transitions over the past two million years. In addition, deglaciation—to a lesser extent—accompanies minor warming events that occur during glacial stages. Prior to the current epoch of glacial and interglacial stages, the Earth experienced several periods during which glaciers episodically covered large parts of its surface. There have been at least four such glacial periods during the past one billion years.
Significance for Climate Change
Deglaciation accompanies climate change and can be a cause of climate change. The geological record indicates that, when deglaciation commences, there is typically a climatic turn toward global warming. In other words, after climatic warming initiates deglaciation, the deglaciation itself can create a positive feedback loop engendering further warming. Glaciers are highly reflective of sunlight, contributing to Earth’s albedo (the percentage of sunlight reflected back into space from the planet’s surface). As glaciers melt, white ice and snow are replaced with darker surface elements. Earth’s decreases, and more solar radiation is absorbed and retained by the planet. As the planet warms, more glaciers melt, the albedo decreases even further, and the process continues. Melting glaciers also contribute water to lakes and oceans, which help retain atmospheric heat. Rising sea levels due to glacial meltwater contribute to as well.
Using the modern deglaciation as an example, loss of cover on the land has had and continues to have profound consequences for global climate change. For example, release of water locked up in glaciers has affected the amount of water in the oceans as well as on land, in rivers and streams, and in the form of groundwater. This has affected coastal and interior ecosystems, which are dependent upon water for life. Changing patterns in the distribution of water cause both climates and ecosystems to change.
Deglaciation, as compared to glaciation, can be a relatively rapid process, once the melting triggers feedback mechanisms that increase its pace. The rapid nature of this change has led to disequilibrium conditions on land, such as unstable slopes, high gradients in rivers and streams, and unstable lakes that drain catastrophically. In the biotic realm, rapid deglaciation has led to mass death and mass extinction among plant and animal groups, as well as mass migration of animal populations.
Deglaciation leaves behind profound physical effects of ice movement, such as landscapes altered by the erosive forces of massive ice sheets, depositional landforms created by sediment released from melting ice, and lakes created by the meltwater—including waters from marooned blocks of ice that melt long after the main glacial mass is gone. The resulting altered landscapes generally have low levels of vegetation (at least initially), as well as areas of low elevation where water can accumulate. This type of landscape has a higher capacity to retain radiated heat from the Sun and therefore also contributes to atmospheric warming.
Bibliography
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"Deglaciation." National Geographic, 19 Oct. 2023, education.nationalgeographic.org/resource/deglaciation/. Accessed 17 Dec. 2024.
Ehlers, J., and P. L. Gibbard, eds. Quaternary Glaciations: Extent and Chronology. 3 vols. San Diego, Calif.: Elsevier, 2004.
Garelick, Sloane, et al. “The Dynamics of Warming during the Last Deglaciation in High-Elevation Regions of Eastern Equatorial Africa.” Quaternary Science Reviews, vol. 281, Apr. 2022, p. 107416. doi.org/10.1016/j.quascirev.2022.107416. Accessed 17 Dec. 2024.
Stanley, Steven M., and John A. Luczaj. Earth System History. 4th ed. Freeman/Macmillan Higher Education, 2015.