Download to Ch. 10 Notes

Geology Ch. 10 Notes – Volcanoes
Objectives
1. Explain the factors that determine the type of volcanic eruptions that occur
2. Describe the various types of volcanic materials that are ejected from volcanoes
3. List the three main types of volcanoes
4. Distinguish how different types of volcanic landforms form.
5. Classify intrusive igneous features
6. Describe the major intrusive igneous features
7. Describe the origin of magma
8. Explain the relationship between plate tectonics and volcanoes
9. Explain where intraplate volcanism occurs
10.1 The Nature of Volcanic Eruptions
Factors Affecting Eruptions
 Factors that determine the violence of an eruption
• ______________of the magma
• ______________of the magma
• Dissolved gases in the magma
 Viscosity
• _______________is the measure of a material's resistance to flow.
• Factors affecting viscosity
- ____________(hotter magmas are less viscous)
- ____________(silica content)
1. High___________—high viscosity
(e.g., rhyolitic lava)
2. Low silica—more fluid (e.g., basaltic lava)
Factors Affecting Eruptions
 Dissolved gases
• Mainly water vapor and __________________
• Gases expand near the surface
• A _____________is an opening in the surface of Earth through which
molten rock and gases are released.
• Provide the force to extrude _____________________
 Dissolved gases
• Violence of an eruption is related to how easily gases escape from
magma
- Gases escape easily from __________magma.
- Viscous magma produces a more ___________
eruption.
Volcanic Material
 Pyroclastic Materials
• Types of pyroclastic material
- _____________—fine, glassy fragments
- ____________—frothy, air-filled lava
- ______________—walnut-sized particles
- ______________—pea-sized particles
• Particles larger than lapilli
- Blocks—hardened lava
- ________________—ejected as hot lava
Types of Volcanoes
 The three main volcanic types are shield volcanoes, cinder cones, and
composite cones.
 Anatomy of a Volcano
• A __________is a mountain formed of lava and/or pyroclastic material.
• A ______________is the depression at the summit of a volcano or that
which is produced by a meteorite impact.
• A_________________, or pipe, carries gas-rich magma to the surface.
 Shield Volcanoes
• _________________are broad, gently sloping volcanoes built from fluid
basaltic lavas.
 Cinder Cones
• ________________are small volcanoes built primarily of pyroclastic
material ejected from a single vent.
- Steep slope angle
- Rather small in size
- Frequently occur in groups
 Composite Cones
• ________________are volcanoes composed of both lava flows and
pyroclastic material.
- Most are adjacent to the Pacific Ocean
(e.g., Mt. Rainier).
- Large size
- Interbedded lavas and________________
- Most ___________type of activity
Other Volcanic Landforms
 Calderas
• ___________are large depressions in volcanoes.
• Nearly circular
• Formed by _____________
• Size exceeds ____________kilometer in diameter
 Lava Plateaus
• Fluid basaltic lava extruded from crustal fractures called ___________
10.2 Intrusive Igneous Activity
Plutons
 ___________are intrusive igneous structures that result from the cooling and
hardening of magma beneath the surface of Earth.
• Intrusive igneous bodies, or plutons, are generally classified according
to their shape, size, and relationship to the surrounding rock layers.
 Sills and Laccoliths
• Sills and laccoliths are _____________that form when magma is
intruded close to the surface.
- ____resemble buried lava flows and may exhibit columnar joints.
- Laccoliths are lens-shaped masses that arch overlying strata
upward.
- crustal rocks heated during subduction
- rising, hot mantle rocks
Origin of Magma
 Role of Water
• Causes rock to ___________at a lower temperature
• Plays an important role in _________________
ocean plates
10.3 Plate Tectonics and Igneous Activity
Convergent Plate Boundaries
 The basic connection between plate tectonics and volcanism is that plate
motions provide the mechanisms by which mantle rocks melt to generate
magma.
 Ocean-Ocean
• Rising magma can form _________________in an ocean (Aleutian Islands).
 Ocean-Continent
• Rising magma can form ___________________(Andes Mountains).
Divergent Plate Boundaries
 The greatest volume of volcanic rock is produced along the oceanic ridge
system.
• _________________pulls apart.
• Less pressure on underlying rocks
• Partial _________________________occurs
• Large quantities of fluid basaltic magma are produced.
Intraplate Igneous Activity
 Intraplate volcanism is igneous activity that occurs ______________a
tectonic plate away from plate boundaries.
• Most ______________volcanism occurs where a mass of hotter than normal
mantle material called a mantle plume rises toward the surface.
• The activity forms localized volcanic regions called hot spots.
• Examples include the Hawaiian Islands and the ________________
Definitions
1. Viscosity: a measure of a fluid’s resistance to flow
2. Vent: an opening in the surface of Earth through which molten rock and gases are
released
3. Pyroclastic material: the volcanic rock ejected during an eruption, including ash,
bombs, and blocks
4. Volcano: a mountain formed of lava and/or pyroclastic material
5. Crater: the depression at the summit of a volcano or that which is produced by a
meteorite
6. Shield volcano: a broad, gently sloping volcano built from fluid basaltic lava
flows
7. Cinder Cone: a small volcano built primarily of pyroclastic material ejected from
a single vent
8. Composite Cone: a volcano composed of both lava flows and pyroclastic material
9. Caldera: a large depression typically caused by collapse or ejection of the summit
area of a volcano
10. Pluton: an intrusive igneous structure that results from the cooling and hardening
of magma beneath the surface of the Earth
11. Sill: a tabular igneous body formed when magma is injected along sedimentary
bedding surfaces
12. Laccolith: a massive igneous body intruded between preexisting strata
13. Dike: a tabular –shaped intrusive igneous feature that occurs when magma is
injected into fractures in the surrounding rock, cutting across preexisting rock
14. Batholith: a large mass of igneous rock that formed when magma intruded at
depth, became crystallized, and subsequently was exposed by erosion: Batholiths
have a surface greater than 100 square kilometers
15. Geothermal Gradient: the gradual increase in temperature with depth in the crust:
the average is 300 C per kilometer in the upper crust
16. Decompression Melting: melting due to a drop in confining pressure that occurs
as rock rises
17. Intraplate volcanism: igneous activity that occurs within a plate away from a plate
boundary