Ch.6, Sec.3 – Causes of Volcanic Eruptions

The Formation of Magma

- changes in the pressure & temperature of the mantle cause magma to form

- soft, igneous rock remains a solid in the Earth because of the intense pressure caused by the weight of the rock above it

- magma is usually created in a liquid form at a plate boundary where the pressure is less and the magma can become less dense and rise to the surface

Ch.6, Sec.3 – Causes of Volcanic Eruptions

Where Volcanoes Form

- the majority (95%) of volcanoes form on the boundary between tectonic plates, like along the Ring of Fire

Ch.6, Sec.3 – Causes of Volcanic Eruptions

When Tectonic Plates Separate

- deep cracks, or rift zones, often will form at divergent plate boundaries

- most of the volcanic activity on Earth occurs at the mid-ocean ridges along a divergent plate boundary

Ch.6, Sec.3 – Causes of Volcanic Eruptions

When Tectonic Plates Collide

- as oceanic crust is subducted under a continental plate, the pressure and temperature increases

- the increase in pressure & temperature allows the water in the oceanic crust to be released

- once released, the water mixes with mantle rock, lowering the rock’s melting point, causing it to melt into magma

Ch.6, Sec.3 – Causes of Volcanic Eruptions

Hot Spots

- some volcanoes can occur in spots very far away from tectonic plate boundaries in areas called hot spots

- scientists are not sure if they form from cracks in the crust or from mantle plumes rising to the surface

- the Hawaiian Islands & Yellowstone National Park in Wyoming are underneath hot spots

Ch.6, Sec.3 – Causes of Volcanic Eruptions

Predicting Volcanic Eruptions

- the three classes of volcanoes are extinct, dormant, and active (scientists study dormant & active volcanoes)

- small earthquakes are a good sign a volcano will erupt soon

- changes in the gasses found in the magma (sulfur dioxide & carbon dioxide) also can signal a possible eruption

- we can also use GPS to monitor any changes in a volcano’s slope angle

Ch.6, Sec.3 – Causes of Volcanic Eruptions

Ch.6, Sec.3 – Causes of Volcanic Eruptions