Final answer:
The two basic eruptive styles of volcanoes are effusive eruptions and explosive eruptions. Effusive eruptions involve low gas content magma that flows easily, while explosive eruptions involve high gas content magma that builds up pressure and results in violent explosions.
Step-by-step explanation:
The two basic eruptive styles of volcanoes are effusive eruptions and explosive eruptions. Effusive eruptions occur when magma is low in gas content and flows easily out of the volcano. The lava flows slowly down the sides of the volcano, creating shield volcanoes with gently sloping sides, like those found in Hawaii. Explosive eruptions occur when magma is high in gas content and cannot flow easily. This builds up pressure inside the volcano until it explodes violently, sending volcanic ash, rock fragments, and gases into the air. Explosive eruptions can create stratovolcanoes with steep sides, like Mount St. Helens.