The Power of Erosion (MT) EarthCache

The Power of Erosion

This is an EarthCache, there is no physical container. To log it, you must go to the location indicated by the coordinates and answer the following questions:

1. Match the sentence (one of them is false) to the Waypoint (see where the waypoints are):
   1. It is formed as a result of the vortex movement of water loaded with rock material.
   2. It is evidence of the existence of regressive erosion in this place.
   3. It was cut out of alluvium previously deposited by flowing water.
   4. It was formed as a result of lateral erosion.
2. Standing at the coordinates, look around and tell me what dominant type of erosion you see?
3. What erosion mechanisms do you think are dominant here?
4. Take a picture of yourself or your nickname with the canyon and/or arch in the background.

The following text and observation of your surroundings may help you answer this question.

Everyone is probably drawn to this place by the impressive size of the Wied Il-Mieleh rock arch. No wonder, because it is a beautiful emanation of the forces of nature. As we walk along the path from the parking lot to the window, it’s worth taking a closer look at what we see on our left.. Because it is also a manifestation of the powerful forces at work.

Fluvial erosion is the process of gouging the Earth's surface, consisting of widening and deepening the channel as a result of the hydraulic, mechanical and chemical activity of flowing water. Fluvial erosion is the most important factor destroying the Earth's surface, and can only be compared to the activity of glaciers during ice ages. The course and extent of erosion depend on:

• • Water flow speed – this is strictly dependent on the amount of water and the slope of the terrain. The greater the amount and slope, the greater the effects of erosion.
  • Quantity and quality of material dragged by the river – the harder and more sharp-edged the rock fragments, the greater the erosion. However, there must always be less debris than the river can carry.
  • Resistance of bedrock – the bed can be cut in solid rock, and these are more difficult to destroy than, for example, an alluvial bed, i.e. cut in older river deposits.

The most important erosion mechanisms are:

• • Abrasion – consists of deepening the bottom as a result of hitting and scrubbing with rock material carried by the river. Crumbling, chipping, tearing out of crumbs and stripping of the substrate occur.
  • Evorsion – i.e. deepening of the bottom of the riverbed as a result of the vortex movement of water loaded with thick rock material. Deepening is done by horizontal eddies – bottom eddies, e.g. at the foot of waterfall thresholds, as well as vertical eddies – descending. In this way, a bottom depression of various sizes and shapes is created, these are potholes.

• • Cavitation – this is a process that allows for the crushing and tearing out of rock fragments, as a result of the implosion of a vacuum created by the different speeds of water molecules in a strongly disturbed stream. For example, a sudden drop in water speed at waterfalls.
  • Hydraulic scouring – the movement of water causes the scouring of the bottom of the alluvial channel
  • Undercutting of the banks – i.e. widening of the channel banks through the mechanical and hydraulic activity of water

There are three types of river erosion:

• • Down-cutting erosion – consists of deepening the bottom of a riverbed made of rocks through gouging (mainly abrasion, evorsion, cavitation) or cutting the river deposited at the bottom of river sediments, the so-called alluvia.
  • Lateral erosion – along the course, the river loses its momentum, although the mass of moving water increases, the riverbed ceases to be deepened, but erodes the banks to a greater extent. Lateral erosion occurs at different speeds depending on the strength of the river, the amount of material carried and, above all, the structure of the bank itself. In the case of a rocky bank, erosion takes the form of mechanical gouging through the impacts of both the mass of water itself and the impacts of the dragged material. In the case of alluvial or earthen banks, the main destructive factor is hydraulic erosion. Undercutting the banks causes the sediments to crumble, slide and drain into which the river cuts. The banks are washed out during high water levels, and at low water levels they are subject to landslides. Particularly strong lateral erosion occurs in winding rivers, and the water primarily undercuts concave sections of the bank.

• • Regressive erosion – involves the extension of a river valley due to the retreat of waterfalls, thresholds and rock breaks. The rate of erosion depends on the amount of water flowing in the riverbed and the hardness of the rocks that form the threshold of the waterfall. Niagara Falls retreats by about 0.8 m per year, and in about 25 thousand years it will disappear altogether.

When you visit Earth Cache you can see not only the amazing work of the ocean, but also the powerful destructive forces that lie dormant in the rivers.