Volcanoes

7.2 Volcanic Eruptions

Types of Lava• Mafic Lava: rich in magnesium and iron– Forms much of the oceanic crust

• Felsic Lava: rich in silica (less magnesium and iron)– Forms much of the continental crust

What determines the type of Volcanic Eruption?

Composition of lava (mafic or felsic ) determines the type of eruption.

• Mafic Lava- hot and thin, flows similar to water– Creates quiet eruptions

• Felsic Lava- thick, viscous and cooler. Contain large amounts of trapped gasses. These gasses boil out explosively. – Creates explosive eruptions– Pyroclastic Material: rock fragments ejected into the air

Journal

• Which lava flows easily creating quiet volcanic eruptions?

• Which lava erupts violently?

Pyroclastic Material Classified based on size:

• Lapilli- less than 64 mm in diameter• Volcanic ash – less than 2 mm in diameter• Volcanic dust – less than 0.25mm in diameter

Types of Volcanoes

• Shield• Cinder-Cone (or Dome)• Strato-volcanoes or composite volcanoes

Shield Volcanoes

• Broad base and gentle sloping sides• Formed by mafic lava

Cinder-Cone Volcanoes

• Steep slopes • Formed by felsic lava

Strato-volcanoes (or composite volcanoes)

• Formed by both smooth lava flows and explosive pyroclastic eruptions

• Form high volcanic mountains

1. Create a quick sketch of the following Volcanoes.2. Name each Volcano type.

Craters and Calderas

• Crater: funnel shaped pit• Caldera: large depression that occurs when a

volcanic cone collapses

Predicting Volcanic Eruptions

• seismographs monitor small earthquakes– number of earthquakes increases prior to volcanic

eruptions

• slight bulging of the surface of the volcano

• composition of gasses given off by the volcano

Journal:

What might an increase in earthquakes near a volcano indicate?

7.3 Volcanoes not on Earth!!!

The moon: Basaltic lava flow on the near side of the moon

• No tectonics or convection currents….. so how could the volcanoes have formed….• May have been caused by intense heat due to meteorite collisions

Mars: Seismically active and Crust is not shifting, produces very large volcanoes

• These volcanoes may still be active.

Io: moon of Jupiter, has active volcanoes. The lava is sulfur based.

• The cause of its warm core is the friction as its surface is pulled back and forth

due to gravitational pull from theother moons and Jupiter.

The End