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 the other moons and Jupiter.

The End