Water is the foundation of life. Without it, there would be no plants, no animals, and no humans. Even the geography of our planet would be different, because water is one of the main forces shaping the landscape. It shapes the land through erosion caused by ice and water, but also through chemical reactions.
Mountain rivers play an important role in this system. In Central Europe and many other parts of the world, much of the precipitation falls in the mountains. From there, entire river systems carry the water down from the mountains, providing water for the agriculture of the lowlands before eventually flowing into larger rivers and, finally, into the sea.
Imagine being a drop of water traveling through this system. What would you see along the way?
Let's start our journey as a water drop!
Our journey begins in winter, when we are a tiny snowflake. Together with millions of other snowflakes, we fall to the ground and land on rocks, trees, and the snow-covered mountains.
We stay there until the snow begins to melt. This is a critical part of the system. Most precipitation occurs during the winter, often within a relatively short period, while the snowmelt takes much longer, starting at lower altitudes and gradually moving up to higher elevations. This means that not all the snow melts at the same time, and the water from the precipitation is released gradually. This natural storage capacity is important because it helps distribute water throughout the seasons.
Unfortunately, this process depends on a very delicate balance and is being threatened by climate change. As temperatures rise, more precipitation falls as rain instead of snow, and the snow melts earlier and faster.
Some of our snowflake friends melt earlier than we do, while others melt later. We are among the last ones to begin our journey down the mountain. Together with a few of our friends, we seep into the soil and flow underground, following the force of gravity.
For a long time, some scientists thought that mountain soils did not play a major role in this process. But they were wrong. More recent studies have shown how important the soil actually is, even though the layer of soil in the mountains can be very shallow.
At some point, we will come back to the surface and continue our journey down the mountain. We might flow over stones, with moss growing alongside our path.
If there is too much water, which can happen during snowmelt or heavy rain, we may even flow through the forest. There are simply too many of us water drops, and the usual riverbed cannot hold us all.
Although we may flow across grass and over other vegetation, this is usually not a problem. It only happens for a relatively short time, and the vegetation is adapted to it. In most cases, it will survive. In places where we flow faster, however, erosion can occur, and we may carry some stones and soil with us.
In these areas, the landscape is very rough, and we flow through waterfalls and gorges and over steep slopes. And we are not the only ones doing this — there are millions of us! Every year! Over time, even rocks can be moved, and that is exactly what we do. We loosen stones and carry them with us. This process is called erosion. Look at the image below to see how water can slowly carve away parts of rocks!
After this first wild phase of gorges and waterfalls, the landscape gradually becomes flatter. Usually, this happens in a larger valley. Our water is very clear and very cold, making us a welcome distraction on hot spring and summer days, especially for young humans.
Here, we flow through a beautiful river. In the background, you can see the mountains, with some of our snowflake friends who will join us later.
However, we are not always as calm and friendly as we look in this photograph. When millions of other water drops melt or fall as rain at the same time, we can become a powerful force! Sometimes, there simply isn't enough space for all of us, and things start to get crowded. We may even carry large stones or fallen trees with us!
Even without water our impact can be clearly seen in the landscape.
A mountain lake gives us a nice break from the constant flow down the mountain. Our very clear water allows fish and other animals to live here.
Let's continue our journey after a break of a few days or weeks. As we flow farther down the mountain, we pass through valleys with different kinds of plants and animals. The impact of humans is already visible. We provide water for all kinds of vegetation, which in turn becomes food for larger animals. Here, cows, which usually live a little farther downstream, enjoy the fresh grass and leaves.
By this point, there is already enough water flowing together that our force becomes interesting to humans as something they can use.
For thousands of years, the rivers in which we flowed downstream have constantly changed their shape and flow through the landscape. When the landscape gets increasingly flat, our energy is not sufficient anymore to transport stones. These stones and gravel gets deposited and have been extracted by humans in gravel pits. After a while, when the gravel is not needed anymore or other factors are more important, the gravel pits will refill with water and build a new ecosystem.
To be continued soon ...