One of the most powerful defensive charms known to wizardkind, the Patronus can also be used as a messenger between wizards. As a pure, protective magical concentration of happiness and hope (the recollection of a single talisman memory is essential in its creation) it is the only spell effective against Dementors.
The wave visible above the level of the water is in fact only part of the wave; the wave extends down through the water column to the ocean floor as well. Waves start out in the deep, open ocean as relatively vertical in shape, Presnell said. As a wave travels toward the shore, though, the bottom part of the wave drags along the ocean floor. The upper part of the wave above the water line starts to move faster than the rest of the wave. As the ocean depth decreases closer to shore, the drag on the wave's bottom becomes stronger, and the upper part of the wave begins to tilt forward.
Waves are created by energy passing through water, causing it to move in a circular motion. However, water does not actually travel in waves. Waves transmit energy, not water, across the ocean and if not obstructed by anything, they have the potential to travel across an entire ocean basin. Waves are most commonly caused by wind. Wind-driven waves, or surface waves, are created by the friction between wind and surface water. As wind blows across the surface of the ocean or a lake, the continual disturbance creates a wave crest. These types of waves are found globally across the open ocean and along the coast.