Final answer:
The Appalachians and many other mountain ranges have been formed mainly due to the collision of tectonic plates, which causes the Earth's crust to fold and create mountains over millions of years.
Step-by-step explanation:
The mountain ranges such as the Appalachians formed primarily because of tectonic plate collisions. When two continental plates converge, the intense pressure causes the earth's crust to fold and buckle, which can create mountain ranges.
This process occurred over millions of years, with the Appalachian Mountains, for example, shaped through a series of tectonic events known as orogenies. These orogenic events include the Taconic, Acadian, and Alleghenian, which contributed to the uplift and subsequent erosion of the mountains.
While other factors like erosion and volcanic activity can affect mountain formation and shape, it is the collision of tectonic plates that is chiefly responsible for creating many of the world’s mountain ranges.