1. Volcano types and projectiles
Eruptions and prediction

2. Lava types
Lava is the material that erupts from volcanoes, and has many different types.
Mafic lava is rich in iron and magnesium, and usually found on oceanic crust.
Felsic lava contains silica and is usually from melted continental crust.
Pahoehoe lava is a rapidly cooling lava that gives a ropey, wrinkly look.
Aa is jagged and blocky.
Pillow lava is circular and cools quickly.

3. Lava types (continued)
Pillow lava on the mid-ocean ridge
Aa lava flowing in Hawaii

4. Eruption differences
Volcanoes that erupt can do so explosively or quietly.
Explosive eruptions tend to happen on continental volcanoes because there are many trapped gases in the lava.
Quiet eruptions tend to happen on oceanic volcanoes (including island volcanoes) and are because mafic lava is very hot and thin, allowing gases to escape easily.
A 10 meter high lava fountain from an explosive eruption

5. Volcanic rock fragments
Tephra particles are rock thrown from volcanoes during eruptions.
It is classified in the following ways, and are all based on the size of the particles.
Tephra is also called pyroclastic material.

6. Tephra classification
Size
Name
0 – 0.25 mm
Volcanic dust
0.025 mm – 2 mm
Volcanic ash
2 mm – 64 mm
Lapilli
64mm >
Volcanic bombs
Volcanic blocks

7. Volcano cone features
Shield volcanoes cover a wide area and result from quiet eruptions. Mafic lava forms a gradually sloped cone.
Cinder cones cover smaller areas but are higher and steeper, made from solid fragments ejected from a volcano.
Composite cones/Stratovolcanoes are formed from both types of eruptions, usually alternating.

8. Volcano cones Shield volcano (top left) Cinder cone (top right)
Stratovolcano (left)

9. Craters and calderas
The vent on the top of a volcano is called a crater.
A caldera is the remnants of a volcano whose cone has collapsed.
Krakatau is the most well-known caldera, sporting a diameter of 6 km.

10. Volcanic eruption prediction
Predicting volcanic eruptions is somewhat possible and semi-reliable.
Small earthquakes near volcanoes usually occur before an eruption, and the more frequent they are, the more likely a nearby volcano will erupt.
Gas emission from craters may indicate an imminent eruption as well.
Geologists also watch for surface bulges on a volcano, usually a sign that lava is building pressure in the crater.