Volcanoes Quiz Lessons 18-21 Quiz Study Guide
1. What is a volcano? What is molten rock?
A volcano is a place on the Earth’s surface where magma is able to come to the surface.
Molten rock is liquid rock. It melts because of the fact that the mantle is hot enough, and under
enough pressure to melt solid rock into liquid
2. What is magma? What is lava? When is magma or lava explosive? p. 224
Magma is melted rock below the surface of the Earth. Lava is melted rock at or above the
surface of the Earth.
2 things affect the explosivity of the volcano:
A. Composition: Magma made of silica rich minerals is thicker, like pudding. It traps
gases, and pressure can build up below this type of magma.
B. Gas content: When more gas is trapped in the magma, pressure builds up. Water
vapor, carbon dioxide, sulfur-based gases are the most common.
3. What are the four signs of a possible volcanic eruption? pp. 200-01
1. Increase in number & magnitude of small, local earthquakes
2. Increase in steam/ash release above the volcano
3. Presence of sulfur in the air above the volcano
4. Bulges in the surface of the volcano
4. What are the three types of volcanoes? Describe each type of volcano, including
explosivity, slope, composition. Give an example of each. pp. 229-231
Shield: Volcano made of layers of lava flows from a non-explosive vent. Low explosivityepisodes of oozing lava. Not steep. Can be tall. Ex: Kilauea, other Hawaiian islands
Cinder Cone: Volcano made of cinders (small volcanic rocks) from an explosive vent. Highmedium explosivity- episodes of shooting lava in the air, cooling into cinders, piling up.
May/may not have oozing lava at base. Steep. Typically short. Ex: Paricutin, Mexico
Composite: Volcano made of alternating layers of lava flows and ash/cinders. High
explosivity- dramatic eruptions. Medium steepness. Tall. Ex: Mt. St Helens, Pinatubo
5. How are volcanoes helpful or constructive? How are volcanoes harmful or destructive?
Helpful/Constructive: Geothermal energy; Soil enrichment; Minerals used in commercial
products like borax, pumice, etc.; New land/ landscapes
Harmful/Destructive: Ash/gases block sun, can be poisonpous, weather/climate change;
Level forests, start fires; Lahar (Hot ash mudflow), mudflows, floods from melted glaciers;
Volcanic tsunamis, etc.
6. Where do you find volcanoes? Why are they located in those places? How does a
subduction zone create volcanoes? pp. 175 and pp.230-31
Volcanoes are found above subduction zones of convergent boundaries due to the melting of the
plate being pushed down into the hot mantle. This usually brings down water from the ocean,
increasing the gas/vapor content.
They are also formed at divergent boundaries where magma rises to the surface as the plates
spread apart.
They are also found above hot spots in the mantle, where the mantle melts through the plate.