Chapter 9: Volcanoes
9.1: How and Where Volcanoes Form
· Volcano
a. Opening in Earth’s crust through which ______, gases, and ash ______
b. The ______that develops around this ______
A. Magma Formation
1. Magma = ______rock, formed deep within Earth
2. Volcanic ______occur when magma rises to the surface
3. Three conditions allow ______to form:
a. ______in pressure ______melting temperatures (mid ocean ridge rift valleys)
b. ______in temperature (hot spot—Hawaiian Islands)
c. ______in amount of water in asthenosphere, ______melting temperatures (subduction boundaries)
4. Magma formation can occur at ______and ______boundaries
5. Once magma forms, it ______to the surface because its density is ______than ______materials
6. Characteristics and rising rates depend on ______content.
B. At Subduction Boundaries
1. Volcanoes always form on the ______plate
2. Oceanic-______collision = volcanoes form on ______
3. Oceanic-______collision = volcanic ______
C. At Divergent Boundaries
1. Lower ______, lower ______point, and high ______cause large amounts of magma to form.
2. Most magma reaches Earth’s surface at ______boundaries (mid-ocean ridges)
3. Mid-ocean ridges are locations of most ______activity
4. ______Mid-Atlantic ridge is above water
D. Over Hot Spots
1. Areas of volcanic activity that result from ______of hot material that have risen from deep in Earth’s ______
2. Sources may be 670 to ______beneath the surface
3. Hot spots remain in the same place as the ______plate moves across it
4. ______Islands formed as the Pacific Plate moved northwest over a ______
5. ______volcanoes lie directly over the hot spot, ______volcanoes or seamounts indicate past location of plate over hot spot
6. ______is the newest volcanic island forming off the coast of ______
9.2: Magma and Erupted Materials
A. Types of Magma
1. ______determines a magma’s viscosity (______to flow)
2. ______silica content magmas ______flow (______viscosity)
· Andesitic and rhyolitic ______
3. ______silica magmas flow more ______(______viscosity)
· Basaltic ______
4. ______(water vapor and carbon dioxide) dissolve in magmas at depths where they form and may ______as the magmas rise
5. Gases escape ______from basaltic magmas, but are more ______released from more ______magmas
6. Basaltic magmas form at ______and oceanic ______
7. Andesitic magmas tend to form at ______boundaries
8. Rhyolitic magmas form where ______underlie ______plates
B. Lava Flows
1. Magma that reaches Earth’s surface is called ______
2. The composition of ______may differ from magma due to materials being ______or ______the magma as it rises
3. Lava Flows on Land
a. Basaltic flows are associated with ______eruptions and form ______rocks as they cool
b. Pahoehoe (formed by basaltic lava at high temperatures flowing quickly out of vents) has ______, ropelike surfaces
c. Aa (formed by cooler basaltic lava that moves more slowly) has ______, jagged surfaces
4. Underwater Lava Flows
a. Forms ______shape—rounded, ______form with a hard crust
b. Results in ______of rounded lumps called ______lava
C. Ash and Rock Fragments
1. When trapped ______are released, solid fragments (pyroclastic material) may be ______
2. Pyroclastic ______are classified by ______
a. ______—diameters less than 2 mm
b. ______—diameters from 2 to 64 mm
c. ______—diameters greater than 64 mm
3. Violent eruptions can create pyroclastic ______(combination of pyroclastic material and ______)
a. Mount ______eruption buried Pompeii under a pyroclastic flow of ______and ______
9.3: Volcanic Landforms
A. Shield Volcanoes
1. ______bases and ______sloping sides
2. ______lava, ______explosive, frequent and copious
B. Cinder Cones
1. Forms when ______lava is thrown into the ______from a vent
2. Lava breaks into ______, hardens, hits the ground
3. Fragments accumulate, forming a ______mound with an ______base
4. ______than other types of volcanoes, form in groups on sides of ______volcanoes
C. Composite Volcanoes
1. Develop when ______of materials from successive explosions accumulate around the ______
2. Composed of ______lava flows and pyroclastic ______
3. Mount ______1980 eruption illustrates forces that shape ______volcanoes
4. Most ______volcanoes have ______eruptions followed by long periods of time remaining relatively ______
D. Calderas
1. Large ______basins formed after the top of a volcano ______
2. ______in Oregon is an example of a ______
3. The caldera in ______National Park is still active
i. Magma ______water feeding ______springs and ______
ii. Estimates indicate the eruption that created Yellowstone caldera was ______times more powerful than the ______Mount St. Helens eruption
E. Lava Plateaus
1. Formed when ______lava pours from a ______in the Earth’s surface
2. Lava spreads across the land, forming the ______
3. ______Plateau (NW United States) is over ______thick and covers 164,000 km2
9.4: Extraterrestrial Vulcanism
A. The Moon
1. ______consist of ______lava flows that occurred 3-4 ______years ago
2. Photographs of an ______crater filled with lava indicate that the lava is ______than the crater
3. ______rock samples of lunar lava are ______billion years old
4. ______lava rock samples are ______billion years old
B. Mars
1. Has numerous ______volcanoes
2. Olympus Mons is the ______known volcano in the ______
i. ______across the base
ii. ______above the surrounding terrain
3. Large size indicates that Mars ______have ______plates
4. Are volcanoes on Mars still ______?
5. Could volcanoes on Mars ______in the future?
C. Venus
1. More than 1600 large ______, most are ______volcanoes
2. ______and ______are also found on the surface
3. Volcanic ______could account for ______surface temperature and accumulated ______in the atmosphere
D. Io
1. One of the most volcanically ______places in the ______
2. Caught in ______tug of war between ______and two other moons
i. Results in parts of Io’s ______moving up and down by as much as ______
ii. Resulting ______is the source of heat that powers ______activity
3. ______temperatures at Pillan Patera volcano may be as high as ______
Chapter 9 Student Notes Volcanoes Page 1 of 3