Volcanoes are a powerful force in nature. They help create our mountains and islands. The gases that were emitted as the earth was forming served to establish the initial atmosphere of earth. They also effect our environment. Large volcanic eruptions put massive amounts of particles into the atmopshere. These particles can cool the Earth's atmosphere. They also enhance ozone depletion in the stratosphere. Below are some examples of how volcanoes effect our environment.
Here is a picture of Mt. Pinatubo as it erupted in 1991.
Here is a picture of the dust cloud from the Pinatubo eruption as seen from space. Notice how the plume has spread over the entire globe. The red areas show regions with high volcanic ash. How many times has the plume circled the earth by this time? For the 3 year period after the eruption we have had cooler global temperatures and enhanced ozobe depletion.