What are moraines

Central moraine

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 generate quite interesting terrain and geomorphologies to discover. One of the elements that are formed close to the glaciers are moraines. It is a mountain range of glacial material that is not stratified. Moraines are classified according to their relationship with the glacier.

In this article we will go deeper into the moraines, what types are there, how they are formed and what is the importance they have for glaciers.

What are moraines

Lateral moraines

The first thing we must be clear about is what a moraine is. It is a small mountain range that is formed with a material that we call till. This till is nothing more than material formed in glaciers and that is not stratified. The material has not been in this area for a long time and has not stratified with the weight of the snow and the passage of the years. If we think about how the dynamics of a glacier work, we will see that an accumulation of snow takes place every year after the winter season. After the snow falls, it accumulates due to the effect of gravity and stratifies with the layers of snow that fell and that have not melted from previous years.

This is how a snowfall profile is established. The deeper we go, the more years back we will be investigating. The set of snow layers is called stratifications. Well, when the rest of the materials are piled up (so to speak) but without being 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

Types of moraines

The characteristics of the moraines are summarized in the content of erratic blocks of ice and materials such as stone fragments that are arranged throughout the entire crossing of the glacier. The ice is dragging the soil materials by its weight and its continuous annual ice and thaw. For this reason, the relief is transformed over the years and years until the glacial valleys and other formations are formed.

The stones of the ablation moraines also present several different types of materials to be found in the glacier bed. Another element that is also called moraine is the sediment that is settled by a glacier. This is because, after all the journey that it has taken from considerable heights, the glacier is dragging all the materials that have been found along the way.

Till dynamics

Entrained sediments

What we call as till are the accumulations of sediments that are originated by the glacier and its dynamics. They can also be called drift or glacier drag when completely heterogeneous groups are formed that are generated in the glacier. The till is the fragment of the glacial drift that has been deposited along the way.

These characteristics mean that the composition of the till is not always the same. We can find mixtures of clay, boulders, gravel and sand. The clay in the tills has a spherical shape after movement and subsequent accumulation. They are called till balls. These balls roll along the bed of a stream and can add rocks to its composition. What this does is that it ends up finishing the entire path covered with rocks.

These till balls are often called armored till balls because they have 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 time of thaw arrives and the glacier begins to melt, the masses of till are dragging and depositing in sandurs of the rivers that come from the glacier. This is more pronounced if it is a continental glacier that begins to melt. Tills can also carry certain alluvial deposits made up of minerals or precious stones. These materials are collected throughout the entire journey of the glacier and acquire great economic value for being something unique. For example, it occurs with diamonds in Wisconsin, Indiana and Canada.

The experts in looking for these minerals focus on following the traces that the tills deposit and use them as clues to know the direction that the glacier has had during the descent down the mountain. Among the most sought after deposits are those of kimberlite, these being those deposits where you can find abundant diamonds or different types of minerals.

There are several cases in which you can find solidified or lithified till. This happens because they have been buried and, with the action of the pressure of the upper layers it has become rock. This type of rock is known as tillite and it is a type of sedimentary rock.

I hope that with this information you can learn more about moraines and tills.


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