As an example, new land masses are formed. The Hawaiian Islands were created by volcanic activity. When volcanoes erupt, the lava releases some healthy gases, including hydrogen and carbon dioxide. When hydrogen mixes with oxygen, it creates water vapor and that starts the water cycle.
Carbon dioxide is used by plants to make food for themselves.
There are many rich deposits found in volcanic bombs and cooled lava that turns into rock. Different metals and gems are found in the rock layers. Copper, silver, and gold have all been found. Some of the world's biggest diamonds come from volcanic rocks. The volcanic chimneys in South Africa and the Soviet Union are filled with diamonds.