Complex sentence: Plateaus can be formed by a number of processes, including upwelling of volcanic magma, extrusion of lava, and erosion by water and glaci, flat areas of rock that are uplifted.
Split into simpler sentences: Plateaus can be formed by a number of processes, including upwelling of volcanic magma, extrusion of lava, and erosion by water and glaciers. Magma rises from the mantle causing the ground to swell upward in really large, flat areas of rock that are uplifted.