Terminal moraines
Definition and Formation
A terminal moraine, also known as an end moraine, is a type of moraine that forms at the snout (outermost edge) of a glacier, marking its maximum advance. This landform is created by the accumulation of unsorted sediments (known as till) that have been transported and deposited by the glacier. Terminal moraines are one of the most prominent types of moraines and are significant in the study of glaciology and geomorphology.
Characteristics
Terminal moraines vary in size and shape, but they typically appear as elongated, arcuate (curved or bow-shaped) ridges of till. They can range from a few meters to tens of meters in height, and from a few hundred meters to several kilometers in length. The composition of a terminal moraine reflects the lithology of the glacier's catchment area, and can include a mix of clay, silt, sand, gravel, and boulders.
Formation Process
The formation of a terminal moraine begins when a glacier starts to retreat, or melt back. As the glacier recedes, it leaves behind a ridge of till at its furthest extent. This ridge marks the glacier's terminal position – hence the name 'terminal moraine'. The process of moraine formation is closely tied to the concept of glacial budget, which refers to the balance between accumulation (the gain of snow and ice) and ablation (the loss of snow and ice) in a glacier.
Types of Terminal Moraines
There are two main types of terminal moraines: recessional moraines and push moraines.
Recessional Moraines
Recessional moraines are a series of terminal moraines left behind by a retreating glacier at points where it paused in its retreat. These moraines are often found in a series, marking the glacier's successive positions during its retreat.
Push Moraines
Push moraines, on the other hand, are formed when a glacier advances, pushing material at its snout into a terminal moraine. This type of moraine is less common than recessional moraines, and is typically associated with surges in glacier activity.
Examples of Terminal Moraines
There are numerous examples of terminal moraines around the world, many of which are significant geological features.
Long Island, USA
One of the most famous examples of a terminal moraine is Long Island, New York, USA. The island's hilly northern region, known as the North Shore, is a terminal moraine formed by the Laurentide Ice Sheet during the last Ice Age.
The Lüneburg Heath, Germany
In Europe, the Lüneburg Heath in northern Germany is a well-known terminal moraine landscape. It was formed by the Scandinavian Ice Sheet during the Pleistocene epoch.
The De Geer Moraines, Sweden
In Sweden, the De Geer Moraines are a series of well-preserved terminal moraines that provide valuable information about the retreat of the Scandinavian Ice Sheet.
Importance in Geology and Environmental Studies
Terminal moraines are important in geology and environmental studies for several reasons. They provide evidence of past glacial activity and can help scientists reconstruct the history of glacier movements. They also serve as natural dams, creating lakes and wetlands that are important habitats for plant and animal species. Furthermore, they influence the hydrology of an area by affecting surface water flow and groundwater recharge.