Mt St.Helens erupted on May 18, 1980, it was a catastrophic event. Mt St.Helens changed the earth gradually over time by building up sediment, ash, and rock over a long period of time then it erupted and rebuild again. Mt St.Helens changed the surface of the earth during an eruption by, filling the rivers near the volcano with mud and layers of ash on the ground. It says, in a paragraph that I found on the internet, "Many of these layers formed as debris slid down the side of the volcano and as mudflows and pyroclastic flows (containing volcanic ash, rock fragments and hot gasses) covered the landscape around the volcano, adding layer apron layer to the surface." Mt St.Helens has changed at different times in history by, when erupting the volcano loses a lot of rock and lets out a lot of ash that changes the shape of the volcano and areas around it. The volcano also would let out lava witch builds up the volcano over time. Another catastrophic event that is going to happen is Mt.Rainier is due for en eruption and and mud flows are going to go as far as Tacoma.