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Volcanoes

Science, Grade 6

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Table Of Contents: Volcanoes

1. Introduction to Volcanoes

2.1. Magma Formation
Magma is a mixture of liquid rock, gases and water formed from intense heat and pressure in the Earth's mantle.
2.2. What Is a Volcano?
A volcano forms when magma moves through the crust and erupts onto the surface of the Earth. Magma that flows onto the Earth's surface is called lava. Layers of cooled lava harden into rock and build up on the earth's surface around a volcano.

2. Volcanoes and Plate Boundaries

3.1. Volcanoes at Plate Boundaries
Most of the Earth's volcanoes are located at tectonic plate boundaries. These volcanoes are found on both continental and oceanic crust.
3.2. Ring of Fire
The belt of volcanoes along the boundary of the Pacific Ocean is called the Ring of Fire because it contains about 75% of the world's active volcanoes.
3.3. Volcanoes at Divergent Boundaries
Mid-ocean ridges form from lava pouring onto the ocean floor at divergent plate boundaries. On land, divergent boundaries produce chains of active volcanoes.
3.4. Volcanoes at Convergent Boundaries
At convergent boundaries, oceanic plates are subducted and magma forms from melting crust. Eruptions create volcanic island arcs in the ocean and volcanic mountain ranges on land.
3.5. Hot Spot Volcanoes
Some volcanoes form over hot spots that are not located along plate boundaries. A hot spot occurs when rising magma is close to the Earth's surface. The islands of Hawaii were formed over a hot spot in the Pacific Ocean.

3. Properties of Magma

4.1. Magma Properties Can Vary
Not all magma is the same. The composition and viscosity of magma can vary. These properties affect how fast the lava flows and the type of volcano that forms.
4.2. Magma Composition
Although magma is a complex mixture, it is primarily composed of silica. Magma can contain from 50 to 70 % silica.
4.3. Magma Viscosity
Viscosity is a liquid's resistance to flow. High viscosity magma is sticky and flows very slowly. Low viscosity magma flows more quickly.
4.4. Different Types of Lava
Magma with high silica content has a higher viscosity and produces light-colored lava that later forms rhyolite. Magma with less silica and a lower viscosity produces dark lava that forms basalt.
4.5. Temperature Affects Magma and Lava
Higher temperatures make magma and lava more fluid, lowering the viscosity. Pahoehoe is a type of very hot, fast-moving lava with low viscosity. Slower-moving, cooler, high-viscosity lava is known as aa.

4. Pause and Interact

5.1. Review
Use the whiteboard tools to complete the activity.

5. Volcanic Eruptions

6.1. Inside a Volcano
Beneath the surface of a volcano is a magma reservoir where rock that is exposed to heat and pressure changes into magma. A long tube through the crust called a pipe connects the reservoir to the surface.
6.2. Vents and Craters
Lava flows out onto the surface through an opening called a vent. Some volcanoes form smaller side vents where lava and gases escape. A cone-shaped depression called a crater often forms during explosive eruptions.
6.3. Why Does a Volcano Erupt?
When magma rises toward the surface, gas bubbles expand and increase in pressure. The force of the gas pushes the magma out of the vent and causes an eruption.
6.4. Quiet Eruptions
There are two types of eruptions—quiet and explosive. Quiet eruptions are non-explosive and occur in volcanoes with low-viscosity, low-silica magma. The fast-moving lava flows out of the vent and across the surface of the land.
6.5. Explosive Eruptions
Explosive eruptions occur in volcanoes with thick, high-viscosity magma that is high in silica. Magma builds up within the volcano's pipe rather than flowing out. Pressure increases until an explosive eruption occurs.
6.6. Pyroclastic Flow and Lahar
Explosive eruptions release a mixture called a pyroclastic flow made up of hot ash, rocks and gases. A fast-moving mudflow called a lahar can also form during an explosive eruption.
6.7. Volcanic Material and Rocks
Volcanic material can be found in all different sizes from tiny ash particles, to cinders, to large pieces called volcanic bombs. Obsidian, pumice, basalt, and rhyolite are all igneous rocks that form from volcanic eruptions.

6. Volcano Classification

7.1. Volcano Classification
Volcanoes are classified by their shape. There are three types of volcanoes—composite, shield and cinder cone.
7.2. Composite Volcano
A composite volcano forms from alternating layers of ash and layers of flowing lava. Composite volcanoes have steep sides and may have a crater on top.
7.3. Cinder Cone Volcano
A cinder cone is a small, steep volcano that is created from the accumulation of ash and pyroclastic material. They often have a crater where the top of the volcano was blown off during an explosive eruption.
7.4. Shield Volcano
Shield volcanoes are wide, flat volcanoes formed by non-explosive lava flows. Layers of hardened lava result in a gently sloping mountain. The Hawaiian Islands were formed from shield volcanoes.

7. Life Cycle of a Volcano

8.1. Stages of Activity
Volcanoes have different stages of activity. An active volcano is one that is erupting or showing signs of erupting soon. A dormant volcano has not erupted for a while, but is expected to erupt in the future. An extinct volcano will probably never erupt again.
8.2. Monitoring Volcanoes
Geologists use a variety of technical instruments to study volcanoes and predict eruptions. Earthquakes, increases in ground temperature and escaped gases provide warning signals of potential eruption.
8.3. Destruction Caused by Volcanoes
Volcanoes can cause widespread damage. Huge clouds of ash may bury towns, and volcanic gases can be deadly. A lava flow covers everything in its path and can start fires and landslides.

8. Pause and Interact

9.1. Review
Use the whiteboard tools to complete the activity.
9.2. Structure of a Volcano
Click on the Terms button. Then click and drag each term to the correct box. Use the reset button to clear the terms and start over. Use the gear button to customize the draggable terms.
9.3. Types of Volcanoes
Follow the onscreen instructions.

9. Volcanic Landforms, Hot Springs and Geysers

10.1. Caldera
After an eruption, the magma reservoir of a volcano may be partially emptied. Some volcanoes collapse into this chamber, forming a large depression on the surface called a caldera.
10.2. Volcanic Necks and Dome Mountains
Volcanic necks are the remnants of a volcanic plug within a previously active volcano. The hardened magma is exposed by weathering and erosion. A dome mountain is magma that hardens below the crust and is uplifted.
10.3. Hot Springs and Geysers
Magma that exists very close to the Earth's surface can warm the groundwater. Hot springs and geysers are formed when this water emerges on the surface of the Earth.

10. Vocabulary Review

11.1. Vocabulary Matching Review
After an eruption, the magma reservoir of a volcano may be partially emptied. Some volcanoes collapse into this chamber, forming a large depression on the surface called a caldera.

11. Virtual Investigation

12.1. Volcano Simulator
The amount of silica and the amount of dissolved gases are two important properties of magma. In this virtual investigation you will study simulated volcanoes by selecting the composition of the magma and then making predictions about a volcano with this type of magma. After watching a simulated volcano erupt, you can determine if your predictions were correct.

12. Assesment

13.1. Volcanoes
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