Ash plumes may reach 50,000 feet. Questions 8-10, Click on the button in front of each of the correct answers. Name two reasons that volcanic eruptions occur. Earthquakes make cracks in the Earth's Surface. Magma rises up and spills out of those cracks, because it is lighter than the surrounding rocks.
Convection currents carry magma to the surface.
The force of the added magma building up there cause the magma to erupt onto the surface. Magma will rise to the surface of the Earth when it is less dense than the surrounding rock in the mantle. When the magma reaches the surface of the Earth the pressure difference between the gases in the magma and the surface pressures allows the magma to boil out. Name the three kinds of volcanic cones. Shield, Cinder, Stratovolcano or Composite cone.