Download magma and lava

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Volcano Review Sheet
Please use your notes, textbook and any diagrams that you may have to help you complete
this review sheet.
1. Molten rock underground is called magma.
2. Mafic magma has low silica and is dark in color.
3. Felsic magma has high silica and is light in color.
4. Define bombs.
A type of tephra that gets ejected from a volcano and is more than 64 mm in size.
(Bombs are in liquid form)
5. There are several shield volcanoes in Hawaii and Mauna Loa is one of them. What type
of eruption does Mauna Loa have and will it explode with a lot of tephra or a little bit
of tephra?
Mauna Loa has a quiet eruption with lava flows.
6. Define viscosity.
Viscosity is the ability to flow. More viscous means it is thicker and is harder to flow. Less
viscous means it is more liquid and can flow easier.
7. List the different types of igneous intrusions.
Laccolith, batholith, dike and sill
8. Where do most of the world’s active volcanoes occur?
Along subduction boundaries
9. Define a hot spot.
Aplace in the mantle where great amounts of heat are rising through the lithosphere.
10.List some names of volcanoes that are located over a hot spot.
Kilauea and Mauna Loa
11.Define sill.
A small body of igneous rock that forms when magma is squeezed into a horizontal crack
and then solidifies (parallel to layers)
12.The depression that results when a volcanic cone collapses over an emptying magma
chamber is called a caldera.
13.Why does magma rise to the surface?
Magma rises because it is less dense than the surrounding material
14.What is the difference between magma and lava?
Magma is molten rock underground and lava is molten rock that reaches or goes above the
surface
15.When lava solidifies it becomes a plutonic igneous rock.
16.What are the two factors that determine how explosive an eruption will be?
The amount of dissolved gases and the amount of silica
17.Magma that squeezes into a vertical crack crossing rock layers and hardening is called
a dike.
18.Why is felsic lava usually associated with explosive eruptions?
Felsic lava is associated with explosive eruptions because it is high in silica which means it is
more viscous. Since it is more viscous the dissolved gases within it cannot escape easily which
results in an explosive eruption.
19.What type of volcano is composed of alternating layers of tephra and lava?
Composite
20.The Hawaiian Islands are made up of what type of volcano?
Shield
21.What type of volcano is composed of entirely tephra?
Cinder Cone
22.What is the name of the depression that results when a volcanic cone collapses over an
emptying magma chamber?
Caldera
23. The indentation at the top of a volcano is called a crater.
24.Why do some volcanoes erupt explosively while others erupt quietly?
It depends on the type of magma/lava that the volcano is made up of. It can either be felsic or
mafic lava.
Felsic lava is associated with explosive eruptions because it is high in silica which means it is
more viscous. Since it is more viscous the dissolved gases within it cannot escape easily which
results in an explosive eruption.
Mafic lava is associated with quiet because it is low in silica which means it is less viscous.
Since it is less viscous the dissolved gases within it can escape easily which results in a nonexplosive eruption.
25.What direction are the Hawaiian islands moving?
Northwest
26.What type of volcano is composed mainly of hardened lava?
Shield volcano
27. Mount St. Helens which erupted on May 18, 1980 is an example of a composite
volcano.
28. Volcanoes that have a slope that angle up to 40 degrees are cinder cone volcanoes.
29. What types of volcanoes occur mainly at hot spots? Shield volcanoes.
30. Composite volcanoes usually occur at subduction zones.
31. Kilauea is an example of a shield volcano
32. Which type of volcanoes make up the tallest mountains in the world?
Composite volcano
33. Cinder Cone volcanoes are made from small explosive eruptions.
*** You should be able to explain the following about each of the three types of volcanoes.
This information should come right from your Note Packet 2 as well as the activity where
you described each type of volcano.
Composite
 Steep sloped sides
 Very tall, 1000s of feet
 Very explosive eruptions, sometimes quiet eruptions (alternating for the most part)
 Made up of alternating layers of lava flows and silica rich (granitic) pyroclastic material.
 Mt. St. Helens is a good example of a composite volcano
Cinder Cone
 Steep sloped sides (angles close to 40°)
 Relative to other volcanoes – small few hundred feet high
 Small explosive eruptions
 Made up of pyroclastic material (ash and tephra)
Shield
 The volcano have a very broad base, with gently sloping side (like a ‘shield’)
 Quiet eruptions
 Made up of layers of hot, mafic (basaltic) lava
 Hawaii is a good example of a shield volcano
1. What it looks likes
2. Origin – location in relation to different plate boundaries
3. Composition – what the volcano is made up of and what type of magma/lava it has
(either felsic or mafic)
4. What type of eruption it has (explosive vs. non-explosive)