# Chapter 5 Study Guide: Volcanoes

Prepare to explain how volcanoes form, compare volcano types and eruption styles, locate volcanic hazards, trace linked effects, identify volcanic benefits, and evaluate monitoring and adjustment strategies.

## Chapter Learning Objectives

The chapter states these objectives. Each section below identifies the objective or objectives it supports.

- **LO:1:** Explain the relationship of volcanoes to plate tectonics.
- **LO:2:** Identify the different types of volcanoes and their associated features.
- **LO:3:** Locate on a map the geographic regions at risk from volcanoes.
- **LO:4:** Describe the effects of volcanoes and how they are linked to other natural hazards.
- **LO:5:** List the potential benefits of volcanic eruptions.
- **LO:6:** Discuss how humans can minimize the volcanic hazard.
- **LO:7:** Recommend adjustments we can make to avoid death and damage from volcanoes.

## 1. Essential Definitions (supports LO:1 through LO:7)

- **Volcanism:** Volcanic activity, including the movement and eruption of magma and lava.
- **Magma:** Molten rock beneath Earth's surface. It contains melted silicate rock and dissolved gases.
- **Lava:** Magma that has erupted onto Earth's surface.
- **Volcanic vent:** An opening through which lava and other volcanic materials reach the surface.
- **Fissure:** An elongated crack that can act as a volcanic vent.
- **Magma chamber:** A near-surface reservoir or pool where magma may accumulate.
- **Decompression melting:** Melting caused by a decrease in pressure on hot mantle rock, commonly where the lithosphere is stretched or at a hot spot.
- **Volatiles:** Compounds such as water, carbon dioxide, and sulfur dioxide that evaporate easily and can exist as gases at Earth's surface.
- **Viscosity:** Resistance to flow. Silica-rich, cooler magma generally has higher viscosity than hot, low-silica magma.
- **Magma evolution:** The change from primitive basaltic magma toward more silica-rich magma as it cools, mixes, and assimilates surrounding crust.
- **Effusive eruption:** A relatively passive eruption in which low-viscosity lava flows onto the surface.
- **Explosive eruption:** An eruption in which volatile-rich, high-viscosity magma fragments and is violently ejected.
- **Pyroclastic debris or tephra:** Rock fragments explosively ejected from a volcano, ranging from ash to lapilli, blocks, and bombs.
- **Ash:** Tephra particles smaller than about 2 mm.
- **Pyroclastic flow:** A fast, hot flow of ash, pumice, rock fragments, and volcanic gas moving down a volcano.
- **Lateral blast:** A sideways explosive blast of hot gas and pyroclastic debris caused by the destruction of part of a volcano.
- **Lahar:** A volcanic debris flow or mudflow made when ash and other loose volcanic material become saturated with water.
- **Jokulhlaup:** An Icelandic term for a large flood caused when volcanic heat rapidly melts snow or glacial ice.
- **Volcanic crater:** A roughly circular depression around a volcanic vent, often formed by explosive extrusion.
- **Caldera:** A large depression formed when a volcano or the land above a partly emptied magma chamber collapses.
- **Stratovolcano or composite cone:** A steep, cone-shaped volcano made of layers of lava and pyroclastic deposits.
- **Lava dome:** A steep-sided mound formed when viscous lava piles up near a vent.
- **Shield volcano:** A broad volcano with gentle slopes built from many flows of low-viscosity basaltic lava.
- **Cinder cone:** A relatively small, steep cone built from loose scoria or other tephra around a vent.
- **Continental caldera:** A broad volcanic depression produced by a very large, explosive eruption and subsequent collapse.
- **Volcanic Explosivity Index (VEI):** A relative scale comparing eruptions using observations such as plume height, ejecta volume, and eruptive violence.
- **Vog:** Volcanic smog, often produced when sulfur dioxide and fine acidic particles pollute the air.
- **Volcanic crisis:** A situation in which scientists judge that an eruption may occur soon and communication and public decision-making become especially important.
- **Forecast:** A probabilistic statement about the likely time, place, and character of an eruption; it is less precise than a specific prediction.
- **Volcanic alert level:** A ground-hazard status used to communicate volcanic conditions. The USGS system uses Normal, Advisory, Watch, and Warning.

## 2. Volcanoes and Plate Tectonics (LO:1)

Most volcanoes occur near active plate boundaries, although volcanoes also form over hot spots. About two-thirds of active volcanoes above sea level are associated with the Pacific Ring of Fire, where subduction is common.

### Where magma forms

Most magma forms in the asthenosphere, the weak mantle layer beneath the lithosphere. The asthenosphere is close to its melting temperature, so changes in pressure, composition, or heat can produce magma. The three principal magma-forming processes are:

1. **Decompression melting:** Pressure decreases as the lithosphere stretches and thins at divergent boundaries or as hot mantle rises at a hot spot. The rock can melt without an increase in temperature.
2. **Addition of volatiles:** Water and other volatiles released from a subducting oceanic plate lower the melting temperature of the asthenosphere. This process produces much of the magma above subduction zones and helps form the Ring of Fire.
3. **Addition of heat:** Rising magma transfers heat to cooler surrounding mantle or crust and may cause that rock to melt. This is especially important where hot spots occur beneath continents.

### Magma composition and behavior

- **Basaltic magma:** About 45-55 percent silica; mafic, hot, and generally low in viscosity. It is the most common magma type and forms basalt.
- **Andesitic magma:** About 55-65 percent silica; intermediate in composition and behavior. It forms andesite.
- **Rhyolitic magma:** More than 65 percent silica; felsic and generally high in viscosity. It forms rhyolite.

As magma rises, cooling, crustal assimilation, and mixing can increase its silica content. Higher silica makes magma more resistant to flow. Volatile content also affects eruption style: low-viscosity, volatile-poor basaltic magma commonly erupts effusively, while high-viscosity magma with abundant dissolved gas is more likely to erupt explosively.

Plate setting therefore influences magma formation, magma composition, volcano shape, and eruption behavior. A divergent boundary commonly produces basaltic, nonexplosive volcanism; a subduction zone commonly produces more volatile-rich, silica-rich magma and explosive volcanoes; and a continental hot spot can produce very large caldera-forming eruptions after magma interacts with thick continental crust.

## 3. Volcano Types, Formation, and Eruptive Behavior (LO:2)

The type of volcano that forms depends on where and how magma forms, how much its composition evolves, and its volatile content. Viscosity and volatile content are the primary controls on whether an eruption is mostly effusive or explosive.

| Volcano type | Typical composition and volatiles | Shape and materials | Typical behavior and examples |
|---|---|---|---|
| Stratovolcano or composite cone | Andesitic to rhyolitic; high volatile content | Steep cone built from layers of lava and pyroclastic deposits | Explosive and effusive eruptions; Mount Shasta, Mount St. Helens, Eyjafjallajokull |
| Lava dome | Andesitic to rhyolitic; low to moderate volatile content | Small, steep-sided dome formed by viscous lava piling up near the vent | Mostly slow effusion, but dome collapse can be explosive; Mount Lassen, Mount Unzen |
| Shield volcano | Basaltic; low volatile content | Broad, gently sloping volcano made of many thin lava flows | Mostly effusive, far-traveling flows; Mauna Loa and Kilauea |
| Cinder cone | Basaltic; low to moderate volatile content | Small, steep cone and summit crater made mostly of scoria and tephra | Mostly tephra ejection with associated lava flows; SP Crater, Paricutin, Eldfell |
| Continental caldera | Rhyolitic; high volatile content | Broad uplift with a large summit depression formed by collapse | Rare, enormous explosive eruptions; Yellowstone and Mount Mazama |

### Features and eruption styles

- A **crater** is generally a smaller depression around a vent, often associated with explosive extrusion.
- A **caldera** is much larger and forms when a magma chamber is partly emptied and the overlying volcano or land surface collapses. Calderas may erupt repeatedly and remain hazardous for very long periods.
- **Hawaiian-type eruptions** are effusive eruptions of low-viscosity basaltic lava, often from shield volcanoes.
- **Icelandic-type eruptions** are effusive basaltic eruptions from an elongated fissure, producing a curtain of fire.
- **Strombolian-type eruptions** are mildly explosive basaltic eruptions commonly associated with cinder cones.
- **Pelean-type eruptions** involve viscous magma, lava-dome growth or collapse, and pyroclastic flows.
- **Plinian and ultra-Plinian eruptions** produce tall eruption columns and abundant pyroclastic debris, commonly from stratovolcanoes or continental calderas.

### Volcanic Explosivity Index

The VEI compares the relative explosivity of eruptions using plume height, volume of ejected material, and the violence of the eruption. Beginning above VEI 2, each step represents about a tenfold increase in ejecta volume. VEI is useful for comparison, but an eruption's danger also depends on location, duration, linked hazards, and exposure.

## 4. Geographic Regions at Risk from Volcanoes (LO:3)

For a map question, locate volcanic regions and connect them to their tectonic settings:

- **Pacific Ring of Fire:** The highest concentration of explosive volcanoes, associated primarily with subduction around the Pacific Basin. Important areas include Alaska, the Pacific Northwest, the Andes, Japan, Indonesia, the Philippines, and New Zealand.
- **Mid-ocean ridges:** Divergent boundaries where decompression melting produces extensive basaltic volcanism. Iceland is an above-sea-level part of the Mid-Atlantic Ridge.
- **East Africa:** Rift-related volcanism occurs where plates are pulling apart.
- **Hawaii:** Volcanism is associated with an oceanic hot spot and produces shield volcanoes.
- **Yellowstone and Long Valley:** Continental hot-spot regions capable of large, infrequent caldera-forming eruptions.
- **Western North America:** In the contiguous United States, the greatest local volcanic hazard is in the Pacific Coast mountains and in areas near Yellowstone and Long Valley. Alaska, British Columbia, and the Yukon also have important volcanic hazards. The Pacific Coast hazard belt extends from northern California through Oregon and Washington into southern British Columbia.

The eastern two-thirds of the United States and Canada are generally free of local volcanic activity, but large caldera eruptions in the western region could spread ash and ash clouds far from the source. Volcanic ash can affect aviation and communities at great distances even when lava and pyroclastic flows remain local.

## 5. Effects of Volcanoes and Linked Hazards (LO:4)

Volcanic effects are commonly divided into primary effects, which result directly from an eruption, and secondary effects, which result from the primary activity or its interaction with the environment.

### Primary effects

- Lava flows
- Pyroclastic activity, including ash fall, pyroclastic flows, and lateral blasts
- Volcanic gases and acidic aerosols

### Secondary effects

- Lahars, debris flows, and mudflows caused by water mixing with ash and loose volcanic debris
- Landslides and volcanic debris avalanches
- Flooding caused by melted snow, ice, or blocked drainage
- Fires ignited by lava, hot pyroclastic material, or volcanic gases
- Tsunamis caused by volcanic collapse, landslides, or explosions entering the sea
- Temporary global cooling after large eruptions inject ash and sulfur dioxide into the atmosphere

### Lava flows and lava tubes

Basaltic lava can move rapidly near a vent, but most lava flows slow considerably as they cool. Pahoehoe has a smooth or ropey surface; aa is cooler, thicker, slower, and blocky. Lava tubes can carry molten rock many kilometers beneath a cooled surface and may leave caverns when the lava drains. Lava flows commonly destroy property and land, but their slow movement often gives people time to evacuate. Lava can also create new black-sand beaches when it enters the ocean.

### Ash fall and pyroclastic debris

Explosive fragmentation produces tephra, ranging from fine ash to lapilli, blocks, and bombs. Ash can cover hundreds or thousands of square kilometers and may reach the upper atmosphere. Its effects depend on the amount and duration of eruption, wind, and distance from the volcano.

Ash fall can:

- destroy crops and vegetation;
- contaminate surface water with sediment and toxic compounds;
- irritate the eyes and respiratory system;
- add enough weight to roofs to cause structural collapse;
- damage engines and shut down aircraft; and
- disrupt transportation and communities far from the volcano.

Pyroclastic flows are among the most lethal volcanic hazards. They are hot, fast mixtures of gas, ash, pumice, and rock that can exceed 400 km/hr and reach temperatures near 1000 C. They may form when an eruption column collapses, when a lateral blast moves sideways, or when a viscous lava dome collapses.

### Gases and lahars

Water vapor and carbon dioxide make up most volcanic gas emissions, but carbon monoxide, sulfur dioxide, hydrogen sulfide, and other gases can also be hazardous. Dense carbon dioxide can collect in low areas and suffocate people and animals, as at Lake Nyos. Sulfur dioxide and acidic particles can produce vog, acid rain, respiratory problems, and contaminated water.

Lahars are generally cooler than pyroclastic flows and can occur during or without an eruption. They form when volcanic ash and other loose material become saturated by melted snow and ice or heavy rainfall. Lahars can travel tens of kilometers down valleys and may reach communities long after an eruption begins. Old lahar deposits are therefore important warning signs for development near volcanoes.

## 6. Linkages between Volcanoes and Other Natural Hazards (supports LO:4)

Volcanoes are linked to their physical environment and to several other hazards:

- Rising magma fractures surrounding rock, so earthquakes commonly accompany or precede eruptions.
- Lava and hot pyroclastic material can ignite vegetation, buildings, and gases, producing fires.
- Eruptions can melt snow and ice, producing jokulhlaups, floods, and lahars.
- Volcanic slopes can fail as landslides or debris avalanches. If material enters the ocean, it can generate a tsunami.
- Lahars can block or fill river valleys, creating later flood hazards.
- Ash and sulfur dioxide can affect air travel, water quality, agriculture, and human health over large areas.
- Large eruptions can produce atmospheric aerosols that temporarily cool global or regional climate.

The 2010 Eyjafjallajokull eruption illustrates several linkages at once: magma interacted with glacial ice, producing floods and fine ash; ash disrupted European air travel; and monitoring of seismic and hydrologic conditions supported warnings and evacuation.

## 7. Natural Service Functions (LO:5)

Volcanic eruptions are hazardous but also provide important benefits:

- Weathering of volcanic rock produces fertile soils that support crops such as coffee, maize, pineapple, sugarcane, and grapes.
- Volcanic heat provides geothermal power for electricity, heating, and industrial processes. Geothermal energy can be renewable when used at a sustainable rate.
- Volcanism produces mineral resources, including metals and materials such as pumice, tuff, perlite, scoria, basalt, and volcanic clay.
- Volcanoes create recreational and educational opportunities through hot springs, spas, hiking, snow sports, tourism, and observation of eruptions.
- Lava builds new land, including volcanic islands such as Hawaii and Iceland and coastal deltas in Hawaii.
- Gases and water vapor released by ancient volcanism contributed to Earth's early atmosphere and hydrologic systems, making conditions for life possible.

These benefits can also increase risk: fertile soil, geothermal resources, and attractive landscapes encourage people to live near active volcanoes.

## 8. Human Interaction with Volcanoes (LO:6)

Unlike some human-influenced hazards, volcanic eruptions cannot currently be prevented or controlled. Human activities do not appear to control the timing or severity of volcanic eruptions. The practical goal is to reduce deaths, damage, and disruption by understanding the hazard and making informed decisions.

Human vulnerability increases when people:

- settle on volcano flanks or in valleys followed by lava flows and lahars;
- build in areas identified by past lava, pyroclastic, or lahar deposits;
- ignore or fail to enforce hazard maps and land-use restrictions;
- underestimate a volcano because it has been dormant for a long time;
- lack evacuation plans, public education, or communication among scientists, officials, media, and residents; or
- allow critical facilities and infrastructure to remain in hazardous locations without protection.

People may choose to live near volcanoes because the soil is fertile, the land is the only available home, the area provides income, or they believe an eruption is unlikely. Age, length of residence, experience, and knowledge can affect how people perceive and respond to volcanic risk.

## 9. Forecasting and Monitoring Eruptions (supports LO:6 and LO:7)

Volcanic forecasting is a probabilistic assessment of the likely time, place, and character of an eruption. It is not a guarantee of the exact time or size of an event. Forecasting is often more successful at volcanoes with a well-understood history, such as Hawaiian volcanoes and Mount Pinatubo.

Scientists monitor:

- **Seismic activity:** Increasing shallow earthquakes, tremors, and earthquake foci that migrate upward can indicate rising magma and fracturing rock.
- **Land-surface changes:** Tilt, swelling, uplift, subsidence, cracks, and other deformation can reveal magma movement. GPS, satellite radar, aerial photography, and other instruments can detect these changes.
- **Thermal, magnetic, and hydrologic conditions:** Heating of rocks, melting snow or ice, changing magnetic properties, and changes in water levels or flow can signal volcanic unrest.
- **Gas emissions:** Changes in the amount or chemical composition of carbon dioxide and sulfur dioxide can indicate changes beneath a volcano.
- **Geologic history:** Mapping and dating old lava flows and pyroclastic deposits reveal the types, sizes, and locations of past eruptions and support hazard maps.

Volcanic activity often gives warning signs, but warning time may be short and not every signal is equally reliable. Mount St. Helens had increasing seismic activity and a growing flank bulge before its 1980 eruption, while the 1991 Pinatubo eruption was forecast well enough to support a large evacuation. The chapter emphasizes that accurate forecasting of most volcanic activity remains difficult.

### USGS alert system

The USGS uses two related four-level systems:

- **Ground alert levels:** Normal, Advisory, Watch, and Warning.
- **Aviation color codes:** Green, Yellow, Orange, and Red.

The two levels usually correspond, but they can differ when the hazard to people on the ground is different from the hazard to aircraft. Ash emissions can create a serious aviation hazard even when ground hazards are limited.

## 10. Minimizing the Volcanic Hazard (LO:6 and LO:7)

Effective volcanic-hazard reduction combines science, land-use planning, communication, engineering, and preparedness.

### Community adjustments

- Map volcanic hazards using geologic history, lava and ash deposits, lahar paths, landslide potential, and likely eruption behavior.
- Keep homes, critical facilities, and infrastructure out of the most hazardous areas when possible.
- Establish evacuation zones, routes, shelters, and transportation plans before an eruption.
- Monitor seismic, deformation, gas, thermal, magnetic, and hydrologic conditions continuously.
- Use sirens, alerts, radio, television, and other communication systems to issue clear warnings.
- Educate residents, visitors, officials, emergency responders, and the media about warning signs and appropriate actions.
- Use automated lahar detection systems and downstream alarms where communities lie in lahar paths.
- Maintain emergency supplies, response plans, drills, and communication among scientists, officials, and residents.
- Use structural controls only where appropriate. Lava-flow diversion and hydraulic chilling have had mixed success and cannot be expected to stop large flows.

Evacuation is the primary adjustment for people in the path of lava, pyroclastic flows, lahars, landslides, toxic gases, or other immediate hazards. The success of evacuation depends on recognizing the warning, communicating it clearly, and leaving before routes are blocked.

### Personal adjustments

Before an eruption:

- Learn the volcano's hazard zones, evacuation routes, and warning systems.
- Take official forecasts and warnings seriously, even if the volcano has been quiet for many years.
- Prepare transportation, emergency supplies, medication, water, food, and communication plans.
- Know whether the home, workplace, school, or travel route lies in a lava-flow, pyroclastic-flow, lahar, flood, ash-fall, or gas hazard area.

During an eruption or warning:

- Evacuate immediately when instructed or when a strong natural warning indicates that you are in danger.
- Move away from the volcano and out of valleys, channels, and other paths followed by lahars or debris flows.
- Follow official routes and do not stop to watch an eruption.
- Avoid pyroclastic flows, lava flows, lahars, volcanic gases, and areas beneath unstable slopes; these hazards may move faster than people can escape.
- Protect breathing and eyes from ash and fumes and follow official instructions about shelter or evacuation.

After an eruption:

- Do not return until officials declare the area safe; lahars, gas, ash, landslides, and renewed eruptions may continue.
- Watch for damaged roads, bridges, utilities, contaminated water, unstable slopes, and roof-loading from ash.
- Continue monitoring official alerts and be prepared for additional evacuation.

## 11. Important Case Studies and Examples (supports LO:2 through LO:7)

- **Eyjafjallajokull, Iceland, 2010:** Increased seismic activity preceded the eruption. A glacial ice cap interacted with erupting magma, producing jokulhlaups and a fine ash plume that shut down air travel across northern Europe. Seismic, GPS, and hydrologic monitoring supported warnings and evacuation.
- **Mount Unzen, Japan:** Earthquake swarms and migrating earthquake foci signaled rising magma. Dome collapse produced pyroclastic flows, while debris-flow channels and evacuation efforts showed both the value and limits of mitigation.
- **Nevado del Ruiz, Colombia, 1985:** An eruption melted snow and ice and generated lahars that buried Armero and killed about 21,000 people. The example shows why old lahar deposits, hazard maps, warnings, and evacuation plans matter.
- **Mount St. Helens, Washington, 1980:** Earthquakes, a growing flank bulge, a massive landslide, a lateral blast, pyroclastic flows, mudflows, flooding, and ash demonstrated how volcanic hazards can cascade. The eruption killed 57 people and caused more than $1 billion in damage.
- **Mount Pinatubo, Philippines, 1991:** Monitoring earthquakes, studying the volcano's history, and educating communities supported the evacuation of more than 60,000 people before a catastrophic eruption.
- **Kilauea, Hawaii:** Long experience with seismic activity, ground deformation, and lava flows makes Hawaiian eruptions comparatively predictable. Lava flows can destroy communities but also create new land and black-sand beaches.
- **Lake Nyos, Cameroon, 1986:** A dense carbon-dioxide release from a volcanic crater lake suffocated people and animals, illustrating that volcanic gases can be hazardous even without an eruptive cone.
- **Eldfell, Heimaey, Iceland, 1973:** Water cooling and barriers slowed and redirected some lava flows, kept a harbor open, and demonstrated the mixed but sometimes useful success of lava-flow control.

## 12. Likely Comparison Questions

Be ready to answer these directly:

- How are magma and lava different?
- How do decompression melting, addition of volatiles, and addition of heat produce magma?
- How do silica content, viscosity, and volatile content affect eruption style?
- How do stratovolcanoes, lava domes, shield volcanoes, cinder cones, and continental calderas differ?
- How does a crater differ from a caldera?
- How do effusive and explosive eruptions differ?
- How does the VEI compare eruptions?
- Why are the Ring of Fire, Iceland, East Africa, Hawaii, Yellowstone, and Long Valley volcanic regions?
- How do lava flows, ash falls, pyroclastic flows, gases, and lahars differ in speed, temperature, reach, and danger?
- How can a volcanic eruption trigger floods, landslides, fires, tsunamis, and climate effects?
- How do volcanoes provide fertile soil, geothermal energy, minerals, recreation, and new land?
- What evidence can indicate that a volcano is reawakening?
- How do ground alert levels differ from aviation color codes?
- Why are evacuation and land-use planning generally more reliable than attempts to control lava flows?
- How did the Eyjafjallajokull, Mount St. Helens, Pinatubo, and Nevado del Ruiz examples demonstrate different hazard-reduction lessons?

## 13. Practice Questions

1. Explain how volcanoes are related to plate boundaries and hot spots.
2. Describe the three principal processes that generate magma.
3. Compare basaltic, andesitic, and rhyolitic magma.
4. Explain how silica and volatile content affect viscosity and eruption style.
5. Compare stratovolcanoes, lava domes, shield volcanoes, cinder cones, and continental calderas.
6. Differentiate a volcanic crater from a caldera.
7. Explain what the VEI measures and why it does not by itself determine total hazard.
8. Locate the Ring of Fire, Iceland, East Africa, Hawaii, Yellowstone, and Long Valley on a map and identify their tectonic settings.
9. Describe the primary and secondary effects of volcanic eruptions.
10. Compare lava flows, ash fall, pyroclastic flows, volcanic gases, and lahars.
11. Explain how a lahar forms and why old lahar deposits are important.
12. Trace a chain of hazards beginning with rising magma.
13. List the natural service functions of volcanoes.
14. Explain why people continue to live near active volcanoes.
15. What observations can indicate that a volcano is reawakening?
16. How can seismic, land-surface, thermal, magnetic, hydrologic, gas, and geologic-history monitoring support a forecast?
17. Explain the USGS ground alert levels and aviation color codes.
18. Why can volcanic forecasts be useful even when exact prediction is not possible?
19. List community actions that reduce volcanic losses.
20. Recommend personal actions before, during, and after a volcanic eruption.
21. Why have lava-flow diversion and hydraulic chilling had mixed success?
22. Use Mount St. Helens, Mount Pinatubo, Nevado del Ruiz, and Eyjafjallajokull to compare warning, evacuation, and linked-hazard outcomes.

## Quick Review Checklist

Before the quiz or test, make sure you can:

- explain the connection between volcanoes and plate tectonics;
- identify the three magma-forming processes;
- compare basaltic, andesitic, and rhyolitic magma;
- connect silica, viscosity, volatiles, and eruption style;
- identify the major volcano types and their features;
- distinguish a crater, caldera, lava dome, pyroclastic flow, lahar, and tephra;
- use the VEI as a relative measure of explosivity;
- locate the Ring of Fire, Iceland, East Africa, Hawaii, Yellowstone, and Long Valley;
- identify primary and secondary volcanic effects;
- trace volcanic linkages to earthquakes, fires, floods, landslides, tsunamis, and climate;
- list volcanic natural service functions;
- explain why human activities generally do not control eruptions but do affect losses;
- describe seismic, deformation, thermal, magnetic, hydrologic, gas, and geologic monitoring;
- distinguish USGS ground alert levels from aviation color codes;
- explain why evacuation, education, land-use planning, and hazard maps reduce risk;
- describe the limits of lava-flow control;
- recommend personal actions before, during, and after an eruption; and
- use the chapter case studies to explain volcanic hazards and adjustments.