Kames are distinctive landforms that provide direct evidence of past ice sheets and glaciers across the landscape. These geological features are irregularly shaped hills or mounds composed of sediment deposited during the final stages of glaciation. They are found across formerly glaciated regions, serving as markers for where ice masses once stood and melted. Understanding how kames form requires examining the unique interaction between flowing water and melting, stagnant ice. Kames belong to a category of deposits known as ice-contact landforms.
What Defines a Kame?
A kame is defined by its physical shape and internal composition of material. The landform typically presents as a conical or irregularly shaped hill with noticeably steep sides. Kames are often found alongside depressions called kettle holes, forming a characteristic “kame and kettle” topography across the terrain.
The material making up a kame is known as stratified drift. This sediment consists mainly of sand and gravel, though it can include silt and cobbles. The term “stratified” indicates that the material was sorted and layered by flowing water before being deposited. This sorting by meltwater distinguishes kames from other glacial hills, such as moraines, which are composed of unsorted, unlayered till dropped directly by the ice.
The size of kames can vary significantly, ranging from small rises to substantial hills, depending on the volume of sediment available. Because the sediments were transported by water, the particles are generally more rounded than the sharp, angular fragments found in deposits left directly by the movement of ice.
The Role of Meltwater and Ice Voids in Formation
The formation of an individual kame is directly linked to the melting of a stagnant or slowly retreating glacier. The process begins with the flow of meltwater, which forms streams that run across the glacier’s surface, within the ice, or beneath it. These meltwater streams carry large amounts of sediment that have been eroded from the underlying bedrock and surrounding landscape.
As the meltwater flows, it seeks out openings and depressions in the ice. Sediment deposition occurs when the meltwater streams lose velocity and energy, often as they flow into a crevasse, a moulin (a vertical shaft in the ice), a hole, or a depression on the ice surface. The water slows down inside these ice voids, dropping its load of sand and gravel, which begins to fill the space.
This sediment accumulation occurs within a temporary container defined by the surrounding ice walls. The material can build up over time, sometimes forming a substantial plug of sediment inside the ice mass. The crucial step in creating the final kame shape happens when the surrounding ice eventually melts away completely.
Once the supporting ice melts, the mass of deposited sediment is lowered to the ground surface. This process of the ice melting around the sediment mass is often accompanied by a slight slumping or collapse of the material. This slumping is what gives the kame its characteristic steep, irregular slopes and conical shape. The steepness of the sides is a direct result of the original ice walls that contained and molded the sediment before they disappeared.
The sorting and layering, or stratification, of the kame sediments are sometimes disrupted during this final collapse, leading to a somewhat chaotic internal structure. This final step leaves a solitary mound on the landscape, a direct cast of the former ice void or depression that it once filled. The presence of kames indicates that the glacier was in a period of melting and stagnation, as active ice flow would likely have destroyed or relocated the fragile sediment deposits.
Kame Terraces and Other Structural Variations
Kames do not always occur as isolated, conical mounds; the depositional environment can lead to different structural variations.
Kame Terraces
One common variation is the kame terrace, which forms along the sides of a valley glacier. This feature develops when meltwater streams flow in the trough created between the lateral edge of the glacier and the adjacent, non-glacial valley wall. The meltwater deposits its sediment load in this narrow, confined space. When the valley glacier melts and disappears, the sediment remains, creating a long, flat-topped, bench-like feature running parallel to the valley side. Kame terraces exhibit a relatively flat surface but feature a steep slope where the ice once stood.
Kame Deltas
Another variation is the kame delta, which forms when a meltwater stream exits the glacier and deposits its sediment into a proglacial lake or pond situated at the ice margin. The stream builds a deltaic fan of sediment, which is often supported by the ice mass on one side. When the ice melts, the delta structure collapses, but the deposited sediment remains as an elevated, flat-topped, and often asymmetrical hill. The resulting landform provides evidence of both glacial activity and the presence of a temporary lake at the ice front.