Mountain building, also known as orogeny, occurs when tectonic plates collide, push against each other, or pull apart. This process can create large mountain ranges over millions of years. The Earth's crust thickens and folds, leading to the formation of peaks and valleys. There are different types of mountain building, including continental collision and volcanic activity. In continental collision, two landmasses push together, forming mountains like the Himalayas. In volcanic activity, magma from beneath the Earth's surface erupts, creating mountains such as Mount St. Helens. Both processes contribute to the dynamic nature of our planet's landscape.