When we talk about a glacial landscape, we analyze some of its components that help us understand its dynamics and evolution. As we know, mountain glaciers create fascinating terrains and geomorphologies. One of the features that form near glaciers are moraines . These are ridges of unstratified glacial material. Moraines are classified according to their relationship to the glacier.
In this article, we'll delve deeper into moraines, exploring their different types, how they form, and their importance to glaciers. For additional information, you can consult the section on glacier formation in general.
What are moraines
The first thing we need to understand is what a moraine is. It's a small ridge formed from a material called till. This till is simply unstratified material formed in glaciers. The material has only been in this area for a short time and hasn't yet stratified under the weight of snow and the passage of time. If we think about how a glacier works, we see that snow accumulates every year after winter. After the snow falls, it accumulates due to gravity and stratifies with layers of snow that fell and haven't melted from previous years. For a deeper understanding of how a glacier forms, we recommend reading about [link to glacier formation].
This is how a snowfall profile is established. The deeper we go, the further back we are investigating. The layers of snow are called stratification . Now, when the remaining materials are piled up (so to speak) but not stratified, it is called till.
There are different types of moraines depending on the relationship it has with the existing glacier. We are going to analyze the different types of moraines:
- Background moraine. It is the type of moraine that forms under the ice of the glacier. This pile of till will be on the bed and will be affected by the melting of the ice and the meltwater flow.
- Lateral moraine. It is the one where the materials are found on the edges of the glacier bed. On the sides of the ice sheets you can see all the materials that make up this moraine.
- Central moraine. When the lateral moraines reach great amplitude, it may happen that they join each other in the center of a valley where two glaciers converge. This union is called the central moraine.
- Terminal moraine. They are made up of glacier debris deposits. They are usually located at the end of the glacier and it is the result of the transport of these materials and the effect of gravity.
- Ablation moraine. They are those that have been deposited on the bed of a glacier.
Key features
The characteristics of moraines can be summarized as the presence of erratic blocks of ice and materials such as rock fragments, which are distributed along the entire length of the glacier. The ice carries these materials from the ground due to its weight and the continuous freezing and thawing cycles of the year. Therefore, the landscape transforms over time until glacial valleys and other formations are created. If you would like to learn more about these valleys, I invite you to take a look at [link/reference].
The rocks in ablation moraines also contain several different types of materials because they are located on the glacier bed. Another element also called a moraine is the sediment deposited by a glacier. This is because, after its long journey from considerable heights, the glacier carries along all the materials it encounters along its path.
Till dynamics
What we call till are the accumulations of sediments that originate from the glacier and its dynamics. They can also be called glacial drift or glacial transport when they form completely heterogeneous deposits generated by the glacier. Till is the fragment of glacial drift that it has deposited along its path.
These characteristics mean that the composition of till is not always the same. We can find mixtures of clay, pebbles, gravel, and sand. The clay in till takes on a spherical shape after movement and subsequent accumulation. These are called till balls. These balls roll down a streambed and can accumulate rocks along the way. This results in the entire path eventually being covered with rocks. To learn more about phenomena like this, you can consult the article on glaciation.
These balls of till are often called armored till balls because they contain more rocks. All this material, called till, is deposited at the end of the moraine, on the sides, in the middle, and at the base. As the thaw season arrives and the glacier begins to melt, the masses of till are carried and deposited in the sandurs of the rivers that flow from the glacier. This is more pronounced if it is a continental glacier that begins to melt. The till can also carry certain alluvial deposits composed of minerals or precious stones. These materials are collected along the glacier's path and acquire great economic value because they are unique. For example, this is the case with diamonds in Wisconsin, Indiana, and Canada.
Experts searching for these minerals focus on following the traces left by the till and use them as clues to determine the direction the glacier has taken as it descended the mountain. Among the most sought-after deposits are kimberlite deposits, where abundant diamonds and various other minerals can be found. More information on this topic can be found in the article about Himalayan glaciers.
There are several instances where you might find till solidified or lithified. This occurs because it has been buried and, under the pressure of the overlying layers, has solidified into rock. This type of rock is known as tillite and is a type of sedimentary rock.
I hope that with this information you can learn more about moraines and tills.
