More than 600 active volcanoes on Earth Kilauea in Hawaii erupts continuously. Iceland is a country that is made entirely from volcanoes.

Volcanic ash and debris can Kill crops and forests Kill people Destroy habitats Sulfuric acid from volcanic gases mixes with water vapor to create acid rain. Gases and ash particles can block sunlight from entering Earths atmosphere lowering the overall temperature of the planet. Watch this pyroclastic flow from Mt. Unzen, Japan:

Soufriere Hills, Montserrat 1995 Volcanologists knew it was about to erupt. Some folks refused to leave. Pyroclastic flows wiped out cities and towns in its path, killing 20 people who ignored the evacuation order.

Plates moving apartdivergent boundaries Icelands volcanoes emerged from seafloor spreading Eyjafjallajökull eruption Plates moving togetherconvergent boundaries Soufriere Hills, Montserrat Hot Spot Volcanoes Hawaiis Kilauea is the most active volcano in the world.

Over a period of about 5 million years, the Pacific plate has moved over a hot spot where mantle material is particularly hot and blasts through Earths crust like a torch. The lava that leaks out at the hot spot built up and formed a volcanic island. As the plate moves over the hot spot, the magma punches through a new spot in the crust, forming new islands. Volcanoes that are no longer over a hot spot become dormant or extinct. The volcanic islands that are quiet begin to erode by the ocean waves.

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An oceanic plates subducting under another oceanic plate will create an island arc.

An oceanic plate subducting beneath a continental plate will create coastal volcanoes.

Shiprock, New Mexico

Devils Tower, Wyoming, a Volcanic Neck

Volcanic Dike near Devils Tower

Another View of the Volcanic Dikes

Yosemite Park, California

The Fish Canyon eruption in southwestern Colorado about 28 million years ago erupted more than 5,000 km 3 (3,107 miles 3 ) of magma from the La Garita caldera. That is enough magma to bury the entire state of California to a depth of nearly 39 feet. Colorado has at least nineteen calderas including one of the worlds largest, the La Garita Caldera. It is so large (22 by 47 miles) that for a long time it was hard for geologists to realize that they were mapping in a giant caldera.

The scale of La Garita volcanism was far beyond anything known in human history. The resulting deposit, known as the Fish Canyon Tuff, has a volume of approximately 5,000 cubic kilometers (1,200 cu mi), enough material to fill Lake Michigan (in comparison, the May 18, 1980 eruption of Mt. St. Helens was only 1.2 cubic kilometers (0.3 cu mi) in volume).

Crater Lake formed around 5,677 (± 150) BC when Mount Mazama exploded. Crater Lake is the deepest lake in the Western Hemisphere and the third deepest in the world. Its deepest point has been measured at 1,949 feet.