This sliding motion is about several cm per year. This continental sliding does not occur smoothly. The motion can build up stresses that are then violently released producing earthquakes. The longer the interval between earthquakes the greater the stresses released. When two thick continental plates collide, the Earth buckles under the pressure, folding the crust and producing mountain ranges.
Volcanoes mark places where molten rock is rising to the surface of the Earth.
Many volcanoes develop at plate boundaries but there are also hot spots located in the center of plates. The Hawaiian island changed formed as a ocean plate slowly moved past a hot spot. The Earth's atmosphere is a mass of air that is continuously weighing down on top of us. We feel its weight through air pressure. We have evolved to exist at the air pressure felt at sea level.