Volcanoes

Volcano is a spot in the crust where molten material (magma) comes to the surface.

Liquid Hot Magma Magma: molten mixture of rock-forming substances, gasses, and water from the mantle. Magma at the Earth’s surface is lava.

Most volcanoes occur around. subduction zones. plate boundaries Most volcanoes occur around *subduction zones *plate boundaries *mid ocean ridges These are called volcanic belts.

The highest concentration of volcanoes occurs in the Ring of Fire in the Pacific Ocean.

Ring of Fire

How it happens Many volcanoes form at boundaries where two tectonic plates collide. Through subduction, the older, denser plates sinks beneath the deep ocean trench into the mantle. Much of the rock melts into magma. Because the magma is hot, it is less dense than the surrounding rock, it rises toward the surface. Eventually, the magma breaks through the ocean floor, creating an eruption.

Hot Spots Some volcanoes do not occur at a plate boundary or subduction zone, but rather in a “hot spot.” They may lie in the middle of tectonic plates. Hot spot: an area where magma deep within the mantle melts through the crust.

Hot spots continued Famous hot spots: Hawaiian Islands and Yellowstone Park Hot spots result in island formation and geothermal activity: hot springs and geysers.

Hawaii’s Island Conveyer Belt

An Eruption example read but don’t write this Ever shake a plastic soda bottle and open it? What happens? It explodes? Why does it explode? Carbon Dioxide!

A Soda Bottle Carbon dioxide is a gas and is dissolved in soda (this is why it is “carbonated”) When you shake the soda, the carbon dioxide comes out of the soda and goes into the air. When you open the bottle, the carbon dioxide is released into the air and the pressure decreases. This is why the soda bottle “explodes”

Volcanoes and Soda Bottles Volcanoes erupt because volcanic gases build up much like carbon dioxide in soda bottles. As magma rises to the surface, the pressure decreases and the gases begin to bubble out of the magma. A volcano erupts when an opening develops in a weak rock. (Bottle is opened).

Types of Volcanoes There are three types of volcanoes and all have their unique properties. The types include 1. Shield volcanoes 2. Cinder Cone volcanoes 3. Composite volcanoes

Shield Volcano Tend to be very wide. Gently sloping. 6-12degrees Usually thin layers of lava pours out of a vent.

Cinder Cone Lava moves fast May explode high into the air. Forms a very steep cone shaped mountain. Produces ash, cinders, blasts These build up around the vent in a steep, conical shape This volcano is found in Az. Last erupted in 1180 Cinder Cone

Composite Lava flows alternate with explosive eruptions of ash Forms a tall cone shaped mountain. Highly explosive and dangerous

After the Lava Flows… Pahoehoe: thick lava that flows very slowly. Aa: thin lava that flows quickly

Pahoehoe

Aa