Modifying agents are those that occur on the surface of the globe and are deeply linked to regional climatic conditions. The rainwater, the sea, the rivers, the winds and the glaciers are continually modifying or sculpting the terrestrial relief , in an incessant work of destruction and construction.
It is important to always consider the different structures of the rocks that suffer this action from nature because, depending on their resistance and the modifying agent, the shape of the relief will have particular features. In tropical regions, for example, with abundant rainfall, rainwater acts as an important modifier. The logic of the erosive action is that of the rounding of the mountains, with filling of the valleys by the sediments that are transported. In the Southeast Region of Brazil, this action gave rise to the so-called “ Mares de Morros em Meia-Laranja”.
On the seafront, the sea wears off the high coasts forming cliffs and sediments the low coasts forming beaches, sandbanks, tokens, etc. The cliffs are steep walls that suffer continuous attack from the waves. On the low coasts, the sea does the work of compensation, increasing the continent.
The rivers, depending on the rocky structures they pass through and the local climates, model valleys of different types: normal , in gutter , in gorge and asymmetrical . Water falls or waterfalls are products of more resistant rock structures that exist in the course of rivers, which facilitates the construction of hydroelectric plants.
The winds continuously transport sediment particles exposed on the surface, forming dunes, in a sweeping work called deflation . The action of the winds, also called wind , is typical of desert and coastal regions. Sometimes, when encountering barriers, the winds sculpt the mountains, polishing them with the particles they transport, in a devastation work called corrosion . Hence there are very curious forms that depend on the direction and intensity of the wind, in addition to the resistance of the rocks. This is the case with cup-shaped figures.
Wind erosion is mainly manifested by the transport of fine material, for example, sand and clay particles from deserts. The sand-laden wind can carve out interesting less resistant sedimentary rocks and varied configurations.
Glaciers, when they collapse in the thawing periods, generally form trough valleys, due to the particularity of the weight and the distribution of the material transported. In coastal regions, ancient glacial valleys can be invaded by the sea, giving rise to the fjords . The most expressive fjords are located in Norway.
| Internal dynamics agents | External dynamics agents |
| Tectonism | Weathering |
| Earthquake or earthquake | Relief modifying agents |
| Volcanism |
The agents of external dynamics occur in nature in an integrated manner. While the weathering is happening continuously, in a work of disintegration of the rocks, in parallel there is the modifying action of the surface, both of rocking and of sedimentation. In a way, weathering prepares the rock for the work to come, “softening” it. Hence the surface layers of the crust, the soils , which are so important for the survival of plant and animal species.
On the other hand, this work, associated with the shaping action of the relief, modifies the rocks, forming a life cycle. The rocks, originally of one type, give rise to others, which in turn also change. And so, what apparently seemed so static and stopped in time, is loaded with mutations.
Now, if we think about the agents of internal and external dynamics, interconnecting them, we will see that they are all associated. They act differently in relation to the time of their actions, however, they work together to give rise to the features of the relief of our planet, which is also in constant transformation.
