The principal agents of erosion of the littoral remain waves, tidal effects and marine currents. The masses of moving water act like "bumper collisons" that alter the rock.

One should not underestimate the importance of chemical degradation of the rock by spray (causing dissolution of material), as is the case for calcereous rock.

The form of the littoral depends on a great many parameters. It could be  something like simple beaches composed of sand or pebble beaches, or it could be a matter of cliffs that have been fashioned by successive rockfalls.

Frozen water occupies a volume 10% greater than when it is in its liquid state.

For this simple reason, water that infiltrates faults or fissures is able to break even the hardest rock during  several cycles of freeze-thaw.  Rocks that have been damaged in this way display breakages that are clean and straight.

This type of degradation of rock is common in mountain regions, where the temperature oscillates regularly around 0° C.

The U-shaped valley is chraracteristic of glacial erosion. The passage of the   gigantic mass of a glacier marks the landscape with imposing tracks. Its abrasive power tears away the walls of blocks of rock. These are crushed and carried downstream.  These are the moraines.

Glaciers are numerous during glacial periods (the last one ended 10,000 years ago). Numerous lakes and fjords bear witness to their presence, long after they have receded.

Thick  sedimentary layers that have accumulated at the bottoms of fjordsand lakes conceal the true depth of the original valley.

The V-shaped valley is typical of one that has been carved by flowing water. The erosion is more pronounced when the water flow is a heavy one, and the water carries suspended particles (sedimentary load).

Sediments torn away from the walls are carried away by the water, downstream, where the speed of the flow is too weak to carry them any further.

The Earth is tilted on its orbit. This causes an unequal amount of sunshine to fall in different parts of the planet during the course of a year, and this is responsible for the seasons. You can use this animation  to illustrate the  variations in the length of daylight,  and the seasons,  in the northern hemisphere.

The circles represented are:

1. Arctic circle (66°N)
2. 45°N latitude (Seattle, Toronto, Milan)
3. Equator
4. Antarctic circle (66°S)

The animation is not drawn to scale for either sizes or distances. Nor are the relative speeds of rotation and revolution accurately represented.

The motions of the Moon around the Earth and of the Earth around the Sun are complex. The motions involved in revolutions are superimposed on the movements involved in rotations. The Earth and the Moon both turn on their own axis (rotation), but both also move around another object (revolution).

The rotation of the Earth (24 hours) explains the alternation of day and night.
The revolution of the Earth around the Sun (365.25 days), because of the inclination of its axis (not shown here), explains the changing seasons.

The fact that the rotation of the Moon on its own axis and its revolution around the Earth both require the same amount of time (29.5 days) explains why the Moon always shows its same side to the Earth.

In this animation, neither proportions nor time scales are accurately presented.

The motions of the Moon around the Earth and of the Earth around the Sun are complex. The motions involved in revolutions are superimposed on the movements involved in rotations. The Earth and the Moon both turn on their own axis (rotation), but both also move around another object (revolution).

The rotation of the Earth (24 hours) explains the alternation of day and night.
The revolution of the Earth around the Sun (365.25 days), because of the inclination of its axis (not shown here), explains the changing seasons.

The fact that the rotation of the Moon on its own axis and its revolution around the Earth both require the same amount of time (29.5 days) explains why the Moon always shows its same side to the Earth.

In this animation, neither proportions nor time scales are accurately presented.

There are more than 1500 active volcanoes on Earth. 95% of these are located at the boundaries of two plates (zones of divergence or of subduction) . The remaining 5% are located  above thermal plumes, in those regions known as “hot spots”.
It is estimated that 80% of these volcanoes lie under the oceans, located along the length of the oceanic ridges. They are at the origin of the material that makes up the ocean floor.
This volcanic activity is one of the numerous phenomena supporting the theory of Plate Tectonics. The gases, ashes and rocks expelled in eruptions are carefully studied in order to better understand the internal composition of the Earth.
Note:  These animations are not necessarily drawn to scale.

Most of the time, there are two  tides each day. The understanding of this complex phenomenon is not simple and many great scientists (Aristotle, Galileo, Newton, Lagrange) attempted to attain that understanding. Gravitation is the force responsible for this phenomenon. The relative positions of the Moon, the Sun and the Earth explain the observed variations in this phenomenon.
Finally, the form of the littoral plays an important role in explaining the different amplitudes observed on the coasts.

The Earth’s surface changes. A simplifed global view illustrate the dynamics of Earth’s interior. Some scale ratios are not respected.