What process causes the continents to drift apart? how?

The continents are not drifting, exactly. They are physically attached to the tectonic plates, which are basically enormous slabs of rock that are stacked on top of each other. The tectonic plates cause the continents to move in a process known as plate tectonics, also causing earthquakes, sink holes, and a number of other natural disasters. I think the best way to make a visualization of this is making a plate of pancakes, and stacking them while only half of each pancake is on top of the previous one, and as it goes up, it becomes more steep, until the point where they fall over.

the process is plate tectonics, a result of Tectonic Activity

to plan an idea out before