The Earth's crust compresses and bends due to tectonic forces through a process called folding. This happens when tectonic plates collide, forcing the crust to fold into anticlines and synclines. Mountain ranges and other geological formations result from folding, such as the Himalayas, created by the Indian and Eurasian plate collision. Subduction is when one plate goes under another, and volcanism is the expulsion of magma.