when volcanoes erupt they emit a mixture of gases, some like ash and sulfur dioxide have a cooling effect bc they reflect sunlight away from the earth others like co2 cause warming by adding to the green house effect

Mount Tambora: 200 years ago, Indonesia

2. Philippines

3. Japan

4. Mexico

5. Ethiopia

The low density of the magma causes it to rise (like air bubbles in syrup) As the magma rises bubbles start to form and the pressure from the gas bubbles bring the magma to the surface and force it into the air, overflowing the volcano