Science Lesson Plan on Types of Volcanoes

Explain to students that there are three different types of volcanoes, classified by the type of lava and eruption that forms each mountain.

Shield Volcanoes

Ask students what type of mountain they think would form if the lava coming out of a volcano was thin and runny, and the eruption was gentle and quiet, not explosive. These are the conditions that form shield volcanoes. To demonstrate this, you can pour several layers of melted wax onto a flat surface. Let each layer harden before pouring the next layer. Students will be able to see how the mountain gradually builds up, but the sides are gently sloping, not steep. The main characteristics of shield volcanoes include:

* Thin, runny lava pours out of a vent in a quiet eruption known as a lava flow
* More layers harden on top of previous layers
* The layers gradually build a wide, gently sloping mountain
* They are called shield volcanoes because they look like a warrior's shield
* Shield volcanoes rising from a hot spot on the ocean floor created the Hawaiian Islands
* Shield volcanoes are the largest of all volcanoes

Examples of shield volcanoes: Mauna Loa, Hawaii; Belknap Shield Volcano, Oregon; Kilauea, Hawaii

Cinder Cones

Ask students what type of mountain would be formed if the lava was a mixture of large and small chunks, and exploded out of the volcano with great force. Cinder cones are formed by explosive eruptions of magma that hardens in the air as it leaves the vent. As a demonstration, you can pour sand or fish gravel into a flat surface, and show that it will pile up and form a steep-sided cone. The main characteristics of cinder cone volcanoes include:

* Thick lava that produces ash, cinders and bombs in an explosive eruption called a pyroclastic flow
* Volcanic ash is made of tiny particles the size of grains of sand; cinders or lapilli are fragments of rock up to 2.5 inches in diameter; volcanic bombs are chunks of rock that range from 2.5 inches up to several meters in size
* These materials accumulate around the vent in a steep, cone-shaped pile
* Cinder cones are the smallest of the volcanoes, usually not more than 300 meters high
* Cinder cones are the most common type of volcano
* There is a large crater at the summit of cinder cone volcanoes
* Cinder cone volcanoes come from a single vent, and often occur on the sides of other types of volcanoes
* Cinder cones usually only erupt one time

Examples of cinder cone volcanoes: Paricutin, Mexico; Amboy Crater, California; Cocoa Crater, British Columbia

Composite or Stratovolcanoes

Composite or stratovolcanoes are formed by both types of lava eruptions, alternating between lava flows and pyroclastic eruptions. Some characteristics of stratovolcanoes include:

* Lava flows (quiet eruptions) alternate with explosive pyroclastic eruptions of ash, cinders and bombs
* Composite volcanoes are tall, cone-shaped mountains in which layers of lava alternate with layers of pyroclastic material
* Stratovolcanoes have a characteristic shape, steeper at the top and spreading out at the base
* Stratovolcanoes may erupt many times over a period of hundreds or thousands of years

Examples of composite volcanoes: Mount Rainier, Washington; Mt. Fuji, Japan; Mt. Etna, Italy

For a list of online resources, see Great Volcano Websites for Teachers and Students

Source:
Earth Science, Holt, Reinhart and Winston. 2007