- Magma forms in the crust and upper mantle where solid rock partially melts. The formation of magma depends on several factors, including heat, pressure, and water content.
- When hot or solid mantle rock is less dense than the surrounding rock, it rises, decreasing the pressure on the rock. This lowers the rock’s melting point, allowing decompression melting to occur.
- Most volcanoes form along divergent and convergent plate boundaries. Some volcanoes form far from plate boundaries above “hot spots” in the crust.
- At divergent boundaries, volcanic activity occurs where the plates pull apart.
- The Ring of Fire is the long belt of volcanoes that circles much of the Pacific Ocean.
- Volcanic activity within a plate can also create volcanism.
- A small volcano opens a few hundred kilometers across that forms above a mantle plume is called a hot spot.
- The primary factors that determine whether a volcano erupts explosively or quietly include characteristics of the magma and the amount of dissolved gases in the magma.
- Viscosity is resistance to motion in a fluid.
- It is used in referring to the Earth’s surface. During explosive eruptions, the gases trapped in magma push the magma out.
- Depending on the type of eruption, volcanoes may produce lava flows or eject pyroclastic materials, or both. All volcanic eruptions also emit large amounts of gases.
- Particles from volcanic eruptions are called pyroclastic materials.
- The highest-speed dusting eruptions range in size from very fine dust and ash to pieces that weigh several tons.
- The three main volcano types are shield volcanoes, cinder cones, and composite cones.
- Repeated eruptions of lava or pyroclastic material eventually build a mountain called a volcano.
Parent Tip: Review the logic above to help your child master the concept of volcanoes and plate tectonics worksheet answers.
