GLG 103 Lab 6. Volcanic Hazards |
Questions and Answers | 2026/2027 Updated
| 100% Correct - Arizona State University.
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
50 exam-style multiple-choice questions. Each question includes the correct answer and a complete rationale
for focused revision.
COVERAGE
GLG 103 Lab 6 examines volcanic hazards, eruptive styles, and hazard assessment. Students interpret
volcano monitoring data, evaluate case studies, and apply plate tectonic and magmatic principles to
real-world eruption scenarios.
STUDY GUIDE
Recommended duration: 2 hours. Passing target: 70%.
HIGHP - Page 1 of 17
,1. A shield volcano in an oceanic hotspot setting produces fluid lava fountains and long
lava tubes. Which combination of magma properties best explains this eruptive style?
[ ] A. High silica, high viscosity, high dissolved gas
[ ] B. Low silica, low viscosity, low dissolved gas
[ ] C. High silica, low viscosity, high dissolved gas
[ ] D. Low silica, high viscosity, low dissolved gas
CORRECT: B. Low silica, low viscosity, low dissolved gas
Shield volcanoes erupt mafic (low-silica) magma with low viscosity and low gas content, allowing lava to flow
long distances and form lava tubes. High-silica magmas are viscous and produce explosive eruptions, not the
effusive style described.
2. A pyroclastic density current (PDC) is approaching a valley community. Which hazard
characteristic makes PDCs more lethal than lava flows?
[ ] A. PDCs move slowly, allowing evacuation
[ ] B. PDCs are confined to summit craters
[ ] C. PDCs travel rapidly and contain hot gas and ash
[ ] D. PDCs only occur underwater
CORRECT: C. PDCs travel rapidly and contain hot gas and ash
PDCs are fast-moving (100-700 km/h) avalanches of hot gas, ash, and rock that can incinerate and
asphyxiate, making them far more lethal than slow lava flows. Lava flows are generally slow enough for
evacuation, and PDCs are not confined to craters.
3. Which monitoring signal most directly indicates that magma is migrating toward the
surface at a restless volcano?
[ ] A. Increased seismic tremor and shallow earthquakes
[ ] B. Decreased gas emissions
[ ] C. Ground subsidence without seismicity
[ ] D. Steady background fumarolic activity
CORRECT: A. Increased seismic tremor and shallow earthquakes
Shallow volcanic earthquakes and harmonic tremor reflect magma and gas movement beneath the edifice,
often preceding eruptions. Decreased gas or subsidence would suggest waning activity, and steady
fumaroles are baseline.
4. A lahar is generated on a snow-capped stratovolcano after a modest eruption. Which
factor most amplifies the lahar's downstream hazard?
[ ] A. Low water content in the volcanic ash
[ ] B. Rapid melting of snow and ice by hot pyroclastic material
HIGHP - Page 2 of 17
, [ ] C. Slow lava effusion that does not interact with ice
[ ] D. Gas emissions that dissipate before reaching the ice
CORRECT: B. Rapid melting of snow and ice by hot pyroclastic material
Lahars form when hot pyroclastic material rapidly melts snow and ice, creating fast-moving volcanic
mudflows that can travel far downstream. Slow lava effusion or dry ash would not generate a significant
lahar.
5. Which tectonic setting is most associated with explosive, high-silica volcanism such as
that of Mount St. Helens?
[ ] A. Mid-ocean ridge
[ ] B. Oceanic hotspot
[ ] C. Continental hotspot
[ ] D. Subduction zone
CORRECT: D. Subduction zone
Subduction zones generate viscous, silica-rich magmas through partial melting of hydrated mantle wedge,
leading to explosive stratovolcanoes like Mount St. Helens. Mid-ocean ridges and hotspots typically produce
mafic, effusive eruptions.
6. A volcanic ash cloud from a large eruption enters the jet stream. Which societal impact
is most likely to occur far downwind?
[ ] A. Immediate lava inundation of cities
[ ] B. Aviation disruption and respiratory health issues
[ ] C. Localized pyroclastic flows
[ ] D. Lahars in distant river valleys
CORRECT: B. Aviation disruption and respiratory health issues
Fine ash can travel thousands of kilometers in the jet stream, disrupting aviation and causing respiratory
problems. Lava, PDCs, and lahars are localized near the volcano and do not affect distant downwind areas.
7. During a volcanic crisis, which combination of monitoring data would most strongly
suggest an imminent explosive eruption?
[ ] A. Decreasing SO2 emissions and ground inflation
[ ] B. Increasing SO2 emissions, ground inflation, and shallow tremor
[ ] C. Steady gas emissions and no deformation
[ ] D. Ground subsidence and decreasing seismicity
CORRECT: B. Increasing SO2 emissions, ground inflation, and shallow tremor
Rising SO2, inflation, and shallow tremor indicate magma ascent and pressurization, signaling an imminent
HIGHP - Page 3 of 17
Questions and Answers | 2026/2027 Updated
| 100% Correct - Arizona State University.
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
50 exam-style multiple-choice questions. Each question includes the correct answer and a complete rationale
for focused revision.
COVERAGE
GLG 103 Lab 6 examines volcanic hazards, eruptive styles, and hazard assessment. Students interpret
volcano monitoring data, evaluate case studies, and apply plate tectonic and magmatic principles to
real-world eruption scenarios.
STUDY GUIDE
Recommended duration: 2 hours. Passing target: 70%.
HIGHP - Page 1 of 17
,1. A shield volcano in an oceanic hotspot setting produces fluid lava fountains and long
lava tubes. Which combination of magma properties best explains this eruptive style?
[ ] A. High silica, high viscosity, high dissolved gas
[ ] B. Low silica, low viscosity, low dissolved gas
[ ] C. High silica, low viscosity, high dissolved gas
[ ] D. Low silica, high viscosity, low dissolved gas
CORRECT: B. Low silica, low viscosity, low dissolved gas
Shield volcanoes erupt mafic (low-silica) magma with low viscosity and low gas content, allowing lava to flow
long distances and form lava tubes. High-silica magmas are viscous and produce explosive eruptions, not the
effusive style described.
2. A pyroclastic density current (PDC) is approaching a valley community. Which hazard
characteristic makes PDCs more lethal than lava flows?
[ ] A. PDCs move slowly, allowing evacuation
[ ] B. PDCs are confined to summit craters
[ ] C. PDCs travel rapidly and contain hot gas and ash
[ ] D. PDCs only occur underwater
CORRECT: C. PDCs travel rapidly and contain hot gas and ash
PDCs are fast-moving (100-700 km/h) avalanches of hot gas, ash, and rock that can incinerate and
asphyxiate, making them far more lethal than slow lava flows. Lava flows are generally slow enough for
evacuation, and PDCs are not confined to craters.
3. Which monitoring signal most directly indicates that magma is migrating toward the
surface at a restless volcano?
[ ] A. Increased seismic tremor and shallow earthquakes
[ ] B. Decreased gas emissions
[ ] C. Ground subsidence without seismicity
[ ] D. Steady background fumarolic activity
CORRECT: A. Increased seismic tremor and shallow earthquakes
Shallow volcanic earthquakes and harmonic tremor reflect magma and gas movement beneath the edifice,
often preceding eruptions. Decreased gas or subsidence would suggest waning activity, and steady
fumaroles are baseline.
4. A lahar is generated on a snow-capped stratovolcano after a modest eruption. Which
factor most amplifies the lahar's downstream hazard?
[ ] A. Low water content in the volcanic ash
[ ] B. Rapid melting of snow and ice by hot pyroclastic material
HIGHP - Page 2 of 17
, [ ] C. Slow lava effusion that does not interact with ice
[ ] D. Gas emissions that dissipate before reaching the ice
CORRECT: B. Rapid melting of snow and ice by hot pyroclastic material
Lahars form when hot pyroclastic material rapidly melts snow and ice, creating fast-moving volcanic
mudflows that can travel far downstream. Slow lava effusion or dry ash would not generate a significant
lahar.
5. Which tectonic setting is most associated with explosive, high-silica volcanism such as
that of Mount St. Helens?
[ ] A. Mid-ocean ridge
[ ] B. Oceanic hotspot
[ ] C. Continental hotspot
[ ] D. Subduction zone
CORRECT: D. Subduction zone
Subduction zones generate viscous, silica-rich magmas through partial melting of hydrated mantle wedge,
leading to explosive stratovolcanoes like Mount St. Helens. Mid-ocean ridges and hotspots typically produce
mafic, effusive eruptions.
6. A volcanic ash cloud from a large eruption enters the jet stream. Which societal impact
is most likely to occur far downwind?
[ ] A. Immediate lava inundation of cities
[ ] B. Aviation disruption and respiratory health issues
[ ] C. Localized pyroclastic flows
[ ] D. Lahars in distant river valleys
CORRECT: B. Aviation disruption and respiratory health issues
Fine ash can travel thousands of kilometers in the jet stream, disrupting aviation and causing respiratory
problems. Lava, PDCs, and lahars are localized near the volcano and do not affect distant downwind areas.
7. During a volcanic crisis, which combination of monitoring data would most strongly
suggest an imminent explosive eruption?
[ ] A. Decreasing SO2 emissions and ground inflation
[ ] B. Increasing SO2 emissions, ground inflation, and shallow tremor
[ ] C. Steady gas emissions and no deformation
[ ] D. Ground subsidence and decreasing seismicity
CORRECT: B. Increasing SO2 emissions, ground inflation, and shallow tremor
Rising SO2, inflation, and shallow tremor indicate magma ascent and pressurization, signaling an imminent
HIGHP - Page 3 of 17
