Volcanoes OBJECTIVES Types of Magma Anatomy of a

Volcanoes OBJECTIVES: Types of Magma Anatomy of a Volcano Types of Volcanoes

Viscosity: Resistance of a liquid to flow There are 3 types of magma. They range from very runny (low viscosity) to very sticky (high viscosity).

Anatomy of a Volcano Lava erupts through an opening called a vent. Over time, the cooled & solidified lava forms a mountain known as a volcano. At the top of the volcano, there is a bowl -shaped depression that can vary in size: Crater: Smaller in size l Caldera: Larger in size. l Over 1 km in size l Forms when top of volcano collapses into the magma chamber. l

Lava vs Magma – molten rocks located within the interior of the Earth Lava – molten rocks located on the surface/exterior of the Earth

Caldera Crater

Anatomy of a Volcano Volcanic fragments thrown into the air during eruptions are called tephra. Can be newly cooled & hardened lava, crystallized mineral grains, or pieces of volcanic cone. l Categorized based on size. l Dust Size: Small l Volcanic Bombs: Large, rounded tephra. l Volcanic Blocks: Large, angular tephra. l

Anatomy of a Volcano Pyroclastic flow are clouds of gas, ash, & other tephra down a slope at incredible speeds. l A. K. A. Rapidly moving volcanic material! l Can cause death & tremendous damage!

Types of Volcanoes Shield Cinder-Cone Composite (Stratovolcano)

Shield Volcano Gently sloping sides Nearly circular base Forms when layers of basaltic lava accumulate during non-explosive eruptions Low viscosity magma: Basaltic Magma Ex. Hawaiian Islands

Cinder-Cone Volcano Forms when material ejected high into the air falls and piles up around the vent. Usually has steep sides Generally small in height Has more silica than shield and large volumes of gases Explosions are more severe than shields: Andesitic Magma

Composite Volcanoes Forms when layers of volcanic fragments alternate with lava. Large amounts of silica and gas: Rhyolitic magma. Much larger than cindercone. Violently explosive: Harmful to humans & environment Ex. Mt. Saint Helens

Where Do Volcanoes Occur? Most occur at plate boundaries 80% along convergent 15%along divergent 5% occur far from plate boundaries.

Convergent Volcanism Circum-Pacific Belt l A. K. A. “Ring of Fire” l Volcanoes of the Western U. S. , Japan, Philippines, & Indonesia l Ex. Mt. Saint Helens Mediterranean Belt l Volcanoes of Italy l Mt. Vesuvius

Ring of Fire

Divergent Volcanism Most occur along ocean ridges. Plates are pulling apart and magma wells up into the gap, producing volcanoes and lava flows.

Hot Spots The volcanoes that are formed far from plate boundaries are formed because of hot spots. Hot Spots: areas of intense magma temperatures. As a plate moves over a hot spot, the temperatures melt the crust and the new magma rises to form volcanoes. When this happens, you get a string of volcanoes Ex. Hawaiian Islands