8 - Earthquakes and Volcanoes

Question 1

Define:

earthquake

Answer 1

The sudden shaking caused by energy release in Earth’s crust.

Earthquakes occur when stress builds up and causes rocks to break, sending seismic waves through the Earth.

Question 2

Identify:

Which plate boundary is most associated with earthquakes?

Answer 2

convergent boundaries

Convergent boundaries involve the collision or subduction of tectonic plates, which generates significant seismic activity, including major earthquakes.

Question 3

Explain:

What are the main earthquake-prone regions on Earth?

Answer 3

• The Ring of Fire
• The Himalayas
• The Alpide Belt
• The Mid-Atlantic Ridge

The Ring of Fire: Encircles the Pacific Ocean; highly active due to subduction zones.

The Himalayas: Caused by the collision of the Indian and Eurasian plates.

The Alpide Belt: Extends from the Mediterranean through Asia due to plate convergence.

The Mid-Atlantic Ridge: A divergent boundary generating seismic activity.

Question 4

True or False:

Earthquakes can occur anywhere on Earth.

Answer 4

True

While most earthquakes occur along plate boundaries, intraplate earthquakes can occur within tectonic plates.

Question 5

Explain:

What are the main factors used to describe earthquake distribution?

Answer 5

• Epicenter
• Focus
• Depth
• Frequency of Occurrence

Epicenter: The point on Earth’s surface directly above the earthquake’s origin.

Focus: The exact location within the Earth where the earthquake begins.

Depth: How deep the earthquake’s focus is, affecting its intensity and impact.

Frequency of Occurrence: How often earthquakes occur in a specific area.

Question 6

Define:

anthropogenic earthquake

Answer 6

An earthquake caused by human activities.

Human activities such as mining, reservoir-induced seismicity, or resource extraction, are usually smaller in magnitude but can still cause significant damage in areas with poorly designed infrastructure.

Question 7

True or False:

Earthquake frequency is constant across the planet.

Answer 7

False

Earthquake frequency, or how often earthquakes occur in a region, varies widely. Areas like the Ring of Fire experience much higher frequencies due to active tectonic boundaries.

Question 8

Identify:

What is the point inside the Earth where an earthquake originates?

Answer 8

focus

The focus, also called the hypocenter, is where the earthquake’s energy is first released, typically several kilometers below the surface.

Question 9

Define:

earthquake magnitude

Answer 9

The measure of energy released during an earthquake.

Magnitude reflects the energy released by an earthquake and is commonly measured using standardized scales that quantify its strength.

Question 10

Identify:

What scale is used to measure the magnitude of earthquakes?

Answer 10

Moment Magnitude Scale

(Mw)

The Moment Magnitude Scale quantifies the energy released during an earthquake and has largely replaced the Richter scale for its accuracy across all magnitudes.

Question 11

Define:

epicenter

Answer 11

The point on the earth’s surface vertically above the focus of an earthquake.

Question 12

Enumerate:

How are earthquakes classified based on their magnitude?

Answer 12

• Small (Less than 3.0)
• Light (3.0–3.9)
• Moderate (4.0–4.9)
• Strong (5.0–5.9)
• Major (6.0–6.9)
• Great (7.0 or more)

Small (Less than 3.0): Often undetectable by humans, recorded only by seismometers.

Light (3.0–3.9): Slight shaking, rarely causing damage.

Moderate (4.0–4.9): Noticeable shaking, minimal damage in well-built structures.

Strong (5.0–5.9): Can cause damage to poorly built structures.

Major (6.0–6.9): Significant damage to buildings and infrastructure near the epicenter.

Great (7.0 or more): Severe damage over large areas, potentially catastrophic.

Question 13

True or False:

A magnitude 6 earthquake releases twice the energy of a magnitude 5.

Answer 13

False

Each magnitude unit represents roughly 32 times more energy release.

Question 14

Define:

earthquake intensity

Answer 14

The severity of shaking experienced at specific locations.

Intensity depends on the distance from the epicenter and local geology. It is often measured using the Mercalli scale.

Question 15

Explain:

What do the Richter scale and Mercalli scale measure?

Answer 15

• The Richter scale measures the magnitude of an earthquake.
• The Mercalli scale measures the intensity or impact of an earthquake.

Question 16

Identify:

What does a high number on the Mercalli scale indicate?

Answer 16

Greater intensity or severe damage caused by an earthquake.

The Mercalli scale ranges from I (not felt) to XII (total destruction), describing the earthquake’s effects at specific locations.

Question 17

True or False:

Deep-focus earthquakes are more destructive than shallow-focus ones.

Answer 17

False

Shallow-focus earthquakes typically cause more damage because they release their energy closer to the Earth’s surface.

Question 18

Define:

seismic wave

Answer 18

A wave that carries energy through Earth from an earthquake or explosion.

Seismic waves are energy waves that travel through the Earth, varying in speed and behavior depending on the materials they pass through.

Question 19

Explain:

What are the 3 main types of earthquake wave patterns?

Answer 19

1. P-Waves (Primary Waves)
2. S-Waves (Secondary Waves)
3. Surface Waves

P-Waves (Primary Waves): Fastest waves, compressing and expanding the ground.

S-Waves (Secondary Waves): Slower waves, moving the ground up and down or side to side.

Surface Waves: Slowest waves, causing the most intense surface shaking.

Question 20

Describe:

What is the primary difference between P-waves and S-waves?

Answer 20

P-waves travel through solids and liquids, while S-waves move only through solids.

P-waves are faster than S-waves and arrive first at seismic recording stations, helping to determine the earthquake’s origin.

Question 21

Identify:

Which type of earthquake wave causes the most damage?

Answer 21

surface waves

Surface waves travel along the Earth’s surface and produce the strongest ground shaking, leading to the most destruction.

Question 22

Identify:

What instrument measures seismic waves?

Answer 22

seismometer

Seismometers record the ground motion caused by seismic waves, and the data collected helps determine the earthquake’s characteristics.

Question 23

Explain:

How does a seismometer work?

Answer 23

By detecting seismic waves using a stationary mass and spring system.

When seismic waves pass through the ground, they cause the base of the seismometer to move, while the mass remains stationary. The relative movement between the mass and the base is recorded, providing data on the intensity and movement of the seismic waves.

Question 24

Define:

seismogram

Answer 24

The record showing seismic wave intensity and arrival times.

Seismograms are used to analyze the strength, timing, and duration of earthquakes and to locate the earthquake’s epicenter.

Question 25

# Define: volcano

Answer 25

A **rupture** in Earth's crust where lava, ash, and gases escape. ## Footnote Volcanoes can *form* at tectonic plate boundaries, hot spots, or rift zones, where magma is forced to the surface.

Question 26

# Explain: What are 4 **types** of **volcanoes**?

Answer 26

1. Composite Volcanoes 1. Shield Volcanoes 1. Cinder Cone Volcanoes 1. Lava Domes ## Footnote **Composite Volcanoes** (Stratovolcanoes): Steep-sided, explosive eruptions with high-viscosity magma. **Shield Volcanoes**: Broad, gentle slopes with non-explosive, low-viscosity lava flows. **Cinder Cone Volcanoes**: Small, steep cones with short, explosive eruptions. **Lava Domes**: Dome-shaped mounds with slow, high-viscosity lava and localized eruptions.

Question 27

# Identify: What **type of volcano** is most likely to **erupt explosively**?

Answer 27

composite volcanoes ## Footnote These volcanoes have steep sides and erupt with high viscosity magma, causing **explosive** eruptions (e.g., *Mount St. Helens*).

Question 28

# Explain: How do **shield volcanoes** form?

Answer 28

From **low-viscosity lava**, forming wide, gentle slopes. ## Footnote They typically produce **non-explosive** eruptions, such as those found in Hawaii (e.g., Mauna Loa).

Question 29

# Define: magma

Answer 29

**Molten rock** beneath Earth's surface that forms lava. ## Footnote When magma reaches the surface, it is called *lava*, and it cools to form igneous rock.

Question 30

# Define: hotspot

Answer 30

* An area deep within the Earth's mantle where unusually hot plumes of magma rise and create volcanoes on the Earth's surface. * Can occur in the middle of plates. ## Footnote *Volcanic hotspots*, like the one beneath the Pacific Plate that created the Hawaiian Islands, remain stationary while tectonic plates move over them, forming chains of volcanoes.

Question 31

# Explain: What are 3 types of **volcanic eruptions**?

Answer 31

1. Explosive eruptions 1. Effusive eruptions 1. Phreatomagmatic eruptions ## Footnote These types vary based on magma composition, eruption force, and water interaction. **Explosive eruptions**: Violent eruptions with gas and ash plumes. **Effusive eruptions**: Gentle lava flows with minimal explosivity. **Phreatomagmatic eruptions**: Explosions caused by water interacting with magma.

Question 32

# Identify: What is the **primary cause** of explosive volcanic eruptions?

Answer 32

High viscosity magma that **traps** gas. ## Footnote The trapped gas builds up pressure in the magma until it is released suddenly, causing explosive eruptions.

Question 33

# Define: pyroclastic flow

Answer 33

A fast-moving **mix** of hot gases, ash, and debris from a volcano. ## Footnote Pyroclastic flows can reach speeds of over **100 km/h** and temperatures of up to **1,000°C**, making them highly dangerous and capable of causing widespread destruction.

Question 34

# Explain: How does **volcanic ash** affect the **environment**?

Answer 34

It causes **respiratory problems**, **disrupts air travel**, and **contaminates water**. ## Footnote *Volcanic ash* can also cause building collapses, damage crops, and contribute to long-term environmental impacts by affecting soil and ecosystems.

Question 35

# True or False: All volcanic eruptions **produce lava**.

Answer 35

False ## Footnote Not all volcanic eruptions produce lava; some may consist entirely of pyroclastic material, gas, and ash.

Question 36

# identify: What is the **opening** where **magma**, **ash**, and **gases** escape?

Answer 36

volcanic vent ## Footnote **Vents** are commonly found at the summit of volcanoes or along fissures in the Earth's crust.

Question 37

# Identify: What are major hazards of volcanic eruptions?

Answer 37

* Lava Flows * Pyroclastic Flows * Ash Clouds * Lahars * Earthquakes ## Footnote **Lava Flows**: Molten rock that destroys everything in its path. **Pyroclastic Flows**: Fast-moving, deadly mix of hot gas, ash, and debris. **Ash Clouds**: Fine particles that disrupt air travel and harm respiratory health. **Lahars**: Mudslides of ash and water, devastating nearby areas. **Earthquakes**: Seismic activity triggered by volcanic movement.

Question 38

# Explain: How do **volcanic eruptions** impact the **climate**?

Answer 38

Releases **sulfur dioxide** and **ash**, causing **temporary global cooling**. ## Footnote The eruption of *Mount Tambora* in 1815 led to the **Year Without a Summer**.

Question 39

# Define: Volcanic Explosivity Index

Answer 39

A scale that measures the **explosiveness** of volcanic eruptions. ## Footnote The *VEI* ranges from 0 (non-explosive) to 8 (extremely explosive), based on the volume of erupted materials and eruption height.

Question 40

# Describe: How do **volcanic eruptions** cause **tsunamis**?

Answer 40

Underwater eruptions **displace water**, generating tsunamis. ## Footnote An example of this is the eruption of **Krakatoa** in 1883, which triggered a massive tsunami.