Mountains form through the collision and uplifting of tectonic plates at plate boundaries. Over time, erosion wears mountains down through processes like water and wind breaking rock into sediment. Mountains can also form through folding of the Earth's crust under pressure. Volcanoes form as molten rock, or magma, erupts through openings in the Earth's crust. The type of volcano that forms depends on the composition and viscosity of the magma. Major volcanic eruptions can have destructive effects on the surrounding land through lava flows and ash falls, but also create fertile soils and new landscapes over time. Eruptions release gases into the air that can impact global climate, and also form features like hot springs and deep sea hydro