18.3 - Volcanoes

Anatomy of a Volcano Lava erupts through an opening called a vent As the lava flows onto the surface it cools and hardens around the vent Over time the hardening lava can accumulate and form a volcano At the top of the volcano a bowl shaped depression, called a crater forms Large craters are called calderas

Shield Volcanoes This has a mountain with a broad, gently sloping side and nearly circular base They form when layer upon layer of basaltic lava during nonexplosive eruptions Hawaii

Cinder-Cone Volcanoes This forms when material ejected high into the air falls back to Earth and piles up around the vents These have steep sides and are generally small These are more explosive then shield volcanoes

Composite Volcanoes These form when layers of volcanic fragments alternate with lava These are much larger then cinder-cone volcanoes and can be very explosive Mount St. Helens