Download Ch.6, Sec.3 * Causes of Volcanic Eruptions

Learning Objectives
 I can describe the formation and movement of magma.
 I can explain the relationship between volcanoes and plate
tectonics.
 I can summarize the methods scientists use to predict volcanic
eruptions.
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