Volcanoes

Volcanoes

By Maribel Marbida

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Learning Objectives

​Define what a volcano is and identify the key parts of a volcano.

​Identify and describe the three main types of volcanoes.

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Learning Objectives

Analyze the positive and negative effects of volcanic eruptions on the environment and human populations​

Observe and explain the process of a volcanic eruption through a hands-on activity, identifying the role of pressure build-up, the movement of magma, and how gases and lava escape.​

Open Ended

What do you think causes a volcano to erupt? What happens inside the Earth that leads to an eruption?

Open Ended

Describe what you imagine, including the effects on the land and the people around it.

• Comes from Vulcan, the Roman god of fire. It is derived from the Latin word "Vulcanus".

• The name was first used in relation to Volcano Island (Vulcano) in Italy.

What is a Volcano?

Multiple Choice

The word "volcano" comes from the name of which Roman god?

• Neptune

• Mars

• Vulcan

• Jupiter

• A weak spot in the crust where molten material, or magma, comes to the surface.

• Magma is a molten mixture of rock-forming substances, gases, and water from the mantle.

• Lava is the magma that reaches the surface. Once it cools, it solidifies into rock.

What is a Volcano?

Multiple Choice

What is a weak spot in the Earth's crust where magma comes to the surface called?

• Earthquake

• Volcano

• Tectonic Plate

• Crater

There are about 600 active volcanoes on land, with many more under the sea. Volcanoes are difficult to observe and map when underwater.

Volcanoes & Tectonic Plate Boundaries

• The Ring of Fire is a major volcanic belt surrounding the Pacific Ocean.

• Volcanic belts form along plate boundaries, where Earth's crust spreads apart or collides.

Volcanoes & Tectonic Plate Boundaries

Multiple Choice

Most volcanic activity around the Pacific Ocean occurs due to movements along plate boundaries where the Earth's crust either collides or spread apart.

• True

• False

Volcanoes form at the mid-ocean ridge as the ocean floor spreads apart, causing a decrease in pressure on the mantle. This process, known as decompression melting, allows magma to form and rise through the gap, eventually erupting to create new oceanic crust.

Spreading Boundaries

Example: volcanoes in Iceland it sits atop the spreading boundary between the North American and Eurasian plates

Multiple Choice

At mid-ocean ridges, the spreading of the ocean floor increases the pressure on the mantle, preventing decompression melting and thus inhibiting the formation of new oceanic crust.

• True

• False

Multiple Choice

Which process best explains how volcanoes form at mid-ocean ridges, such as those in Iceland?

• Subduction melting

• Decompression melting

• Frictional heating

• Conduction heating

Volcanoes often form where two oceanic plates collide or where an oceanic plate collides with a continental plate. In both situations, an oceanic plate sinks beneath a trench. Rock above the plate melts to form magma, which later erupts as lava.

Colliding Boundaries

Example: Mount St. Helens and Mount Rainier

Volcanoes also occur where an oceanic plate is subducted beneath a continental plate. Collisions of this type produced the volcanoes ofthe Andes in South America and the volcanoes of Northern California, Oregon, and Washington.

Multiple Choice

Which process is responsible for forming the volcanoes of the Andes and the volcanoes in Northern California, Oregon, and Washington?

• Hotspot volcanism

• Divergent plate boundary spreading

• Subduction of an oceanic plate beneath a continental plate

• Continental collision

​Mount St. Helens

​Mount Rainier

Multiple Choice

Which of the following best explains how volcanoes like Mount St. Helens and Mount Rainier form?

• They form due to decompression melting at mid-ocean ridges.

• They form when an oceanic plate sinks beneath a continental plate, causing the rock above to melt.

• They form from the collision of two continental plates.

• They form from hot spots in the middle of tectonic plates.

Island Arc - a chain of island that forms as a result of volcanic activity when one tectonic plate slides underneath another.

Examples:
Philippines
Japan
New Zealand
Indonesia
The Aleutians
The Caribbean Island

Multiple Choice

Which of the following is an example of an island arc formed by subduction-related volcanic activity?

• The Mid-Atlantic Ridge

• The Hawaiian Islands

• The Aleutian Islands

• The East African Rift

Multiple Choice

Which of the following is NOT an example of an island arc formed by subduction-related volcanic activity?

• Japan

• New Zealand

• Indonesia

• Mid-Atlantic Ridge

​Hot Spot Volcanoes

​A hot spot is an area where material from deep within the mantle rises and then melts, forming magma.A volcano forms above a hot spot when magma erupts through the crust and reaches the surface.

Example: the Hawaiian Islands and the Yellowstone National Park

Multiple Choice

Which of the following best describes the process of hot spot volcanism?

• An area where material from deep within the mantle rises, melts, and forms magma, leading to volcano formation above the hot spot

• A region where tectonic plates diverge, allowing magma to rise and form new oceanic crust.

• A zone where subducting oceanic plates generate magma as they sink into the mantle, resulting in volcanic arcs.

• A location where two continental plates collide, causing the crust to fold and form volcanoes.

Parts of a Volcano

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• Crater - crater is a bowl-shaped area that may form at the top of a volcano around the central vent.

• ​Magma Chamber - A pocket beneath a volcano where magma collects.

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​Parts of a Volcano

• Pipe - a long tube in the ground that connects the magma chamber to Earth's surface.

• ​Vent - an opening called through which molten rock and gas leave a volcano

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​Parts of a Volcano

Multiple Choice

Which part of a volcano is the bowl-shaped depression at the top that forms after an eruption?

• Magma chamber

• Conduit

• Crater

• Vent

Multiple Choice

Which part of a volcano is the underground reservoir where magma is stored before an eruption?

• Crater

• Vent

• Lava Dome

• Magma Chamber

• Pressure builds up in its magma chamber beneath the surface. As tectonic forces push the plates around, molten rock (magma) collects in this chamber.

• When the pressure becomes too high, the magma forces its way upward through a conduit, traveling along a pipe-like channel.

​How does a volcano erupt?

• It finally escapes through the vent at the volcano’s surface, often carrying gas and volcanic ash along with it.

• This sudden release of pressure results in an explosive or effusive eruption, where lava flows out, creating new rock formations and altering the landscape around the volcano.

​How does a volcano erupt?

Reorder

Rearrange the following statements to correctly describe the process of a volcanic eruption:

• Pressure builds up in the magma chamber.

• Magma travels upward through the conduit.

• Magma escapes through the vent at the volcano’s surface.

• An eruption occurs, releasing lava, gas, and ash.

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2

3

4

• 1
• 2
• 3
• 4

• Pahoehoe (pah HOн ее hoh ee) is fast-moving, hot lava that is thin and runny. looks like a solid mass of wrinkles and rope-like coils.

• ​Aa (AH ah) is cooler and slower-moving. It is thicker than pahoehoe. When it forms a rough surface consisting of jagged lava chunks.

Types of Lava Produced

A volcano erupts quietly if its magma is low in silica. Low-silica magma is thin and runny and flows easily. The gases in the magma bubble out gently. Low-silica lava oozes quietly from the vent and can flow for many kilometers.

​Quiet Eruption

Kinds of Volcanic Eruption

Multiple Choice

What type of lava flow is shown in the picture?

• Aa

• Pahoehoe

Multiple Choice

What type of lava flow is shown in the picture?

• Aa

• Pahoehoe

• Volcanic Ash - fine, rocky particles as small as a speck of dust.

• ​Cinders - pebble-sized particles.

• Bombs - larger pieces that may range from the size of a baseball to the size of a car.

• Pyroclastic Flow - a type of explosive eruption that hurls out a mixture of hot gases, ash, cinders, and bombs.

Types of Lava Produced

A volcano erupts explosively if its magma is high in silica. High-silica magma is thick and sticky. The erupting gases and steam push the magma out of the volcano with incredible force. This eruption breaks lava into fragments that quickly cool and harden into pieces of different sizes.

​Explosive Eruption

Kinds of Volcanic Eruption

Multiple Choice

Which of the following best explains why some volcanoes erupt explosively?

• Their magma is low in silica, allowing it to flow easily.

• Their magma is high in silica, making it thick and sticky, which traps gases that build up pressure.

• Their magma is cooled quickly by ocean water before reaching the surface.

• Their magma contains very little gas, reducing the force of the eruption.

Multiple Choice

Which volcanic product is best described as a fast-moving current of hot gases, ash, cinders, and bombs?

• Volcanic Ash

• Cinders

• Bombs

• Pyroclastic Flow

Cinders

​Volcanic Ash

Types of Lava Produced

Pyroclastic Flow

​Volcanic Bombs

Types of Lava Produced

Multiple Choice

Identify the type of lava shown in the picture

• Volcanic Ash

• Volcanic Cinders

• Volcanic Bombs

• Pyroclastic Flow

Multiple Choice

Identify the type of lava shown in the picture

• Volcanic Ash

• Volcanic Cinders

• Volcanic Bombs

• Pyroclastic Flow

Multiple Choice

Identify the type of lava shown in the picture

• Volcanic Ash

• Volcanic Cinders

• Volcanic Bombs

• Pyroclastic Flow

or live, volcano is one that is erupting or has shown signs that it may erupt in the near future.

​Active

Types of Volcano According to Eruptive History

​Dormant

or sleeping, volcano is expected to awaken in the future and become active.

​Extinct

or dead, volcano is unlikely to erupt again.

Match

Match the following

• Extinct

• Active

• Dormant

unlikely to erupt again

erupting or has signs that it may erupt

expected to awaken

• unlikely to erupt again

• erupting or has signs that it may erupt

• expected to awaken

​Kīlauea (Hawaii)
Active

​Mauna Kea (Hawaii) - Dormant

Shiprock (New Mexico)

These volcanoes have broad, gently sloping sides and are built by the eruption of low-viscosity lava that can flow long distances. The result is a wide, shield-like shape.
Example: Mauna Loa in Hawaii.

Types of Volcanoes

1. Shield Volcanoes

These are characterized by steep, conical shapes with multiple layers of hardened lava, tephra, and ash. They tend to produce explosive eruptions due to the more viscous lava.
Example: Mount St. Helens in Washington.

Types of Volcanoes

2. Composite Volcanoes

Cinder cones are small, steep-sided volcanoes formed from the accumulation of volcanic debris (cinders) around a single vent. They usually have a bowl-shaped crater at the summit.
Example: Parícutin in Mexico

Types of Volcanoes

3. Cinder Cone Volcanoes

Lava domes are formed by the slow eruption of viscous lava that piles up around the vent, creating a rounded, dome-like structure.
Example: The lava dome within the crater of Mount St. Helens.

Types of Volcanoes

4. Lava Domes

Multiple Choice

Which type of volcano is characterized by broad, gently sloping sides formed by the eruption of low‐viscosity lava that flows long distances?

• Composite volcano

• Shield volcano

• Cinder cone volcano

• Lava dome

Multiple Choice

Which of the following best describes cinder cone volcanoes?

• They have broad, low slopes formed by fluid lava flows.

• They are large, layered volcanoes with explosive eruptions.

• They are rounded, dome-like structures formed by viscous lava piling up around a vent.

• They are steep, cone-shaped volcanoes formed by the accumulation of volcanic debris around a single vent.

Multiple Choice

Lava domes are formed by the slow eruption of viscous lava that piles up around the vent, creating a rounded, dome-like structure.

• True

• False

Multiple Choice

Which characteristic of composite volcanoes contributes most to their explosive eruptions?

• They are built primarily from rapidly flowing lava.

• They have a broad, shield-like shape.

• They have thick, high-viscosity lava that traps gases.

• They erupt low-viscosity lava that flows easily.