🌋🧠 EXAM 2 — MULTIPLE CHOICE PRACTICE TEST (75 QUESTIONS)
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75 Terms
What are the two most abundant gases in volcanic emissions?
Water & CO₂
What causes melting at subduction zones?
Water addition
What causes melting at divergent boundaries?
Pressure decrease
Which magma type is least viscous?
Ultramafic
Which magma type has the highest silica content?
Felsic
What does high-viscosity magma tend to do?
Trap gases
Which eruption style is least explosive?
Hawaiian
Which eruption style involves magma interacting with water?
Surtseyan
Which eruption style produces lava fountains and some pyroclasts?
Strombolian
Which eruption style involves a lava dome blocking the throat?
Vulcanian
Which eruption style produces pyroclastic flows named after Mt. Pelée?
Peléan
Which eruption style produces tall ash columns?
Plinian
What are shield volcanoes composed of?
Mafic lava flows
What are cinder cones composed of?
Mafic pyroclasts
What are composite volcanoes composed of?
Alternating pyroclasts + intermediate lava
Why are lava flows rarely deadly?
They move too slowly
What is the deadliest volcanic hazard?
Pyroclastic flows
What is a lahar?
A mudflow of water + volcanic debris
Why can lahars occur without an eruption?
Rain or snowmelt can mobilize ash
What killed 22,000 people in Armero, Colombia?
Lahar
What caused the Lake Nyos disaster?
CO₂ released from magma accumulated in the lake
What saved Heimaey’s harbor in 1973?
Spraying seawater + building barriers
What triggered Eyjafjallajökull’s explosive eruption in 2010?
Glacial meltwater entering magma
What was the first sign of Mt. St. Helens reactivation in 1980?
M3 earthquake swarm
What do most earthquake swarms near volcanoes do?
Rarely cause eruptions
What is mass wasting?
Movement of material downslope by gravity
How is relief created?
Upward and downward displacement
A slope becomes unstable when what occurs?
Shear > resistance
How does water destabilize slopes?
Increasing pore pressure
What effect does a small amount of water in sediment have?
Increases cohesion
Why does saturated sediment fail?
Grains lose contact
How does vegetation stabilize slopes?
Roots holding regolith + absorbing water
What is the angle of repose?
Steepest angle material can hold
What is the angle of repose for rounded sand?
30–37°
What is the angle of repose for angular gravel?
45°
When are slopes most unstable?
When layers are parallel to slope
What is creep?
Slow
What are signs of creep?
Tilted poles
Where does solifluction occur?
Permafrost
What direction does a slump move?
Along a curved surface
What does a debris flow contain?
Water, mud, and large rocks
What is a rockfall?
Free-fall
What are natural triggers of landslides?
All of the above
What are human triggers of landslides?
All of the above
What caused the Lituya Bay megatsunami?
Rockfall from strike-slip fault
What causes tsunamis?
Sudden displacement of water
Where do most tsunamis occur?
Convergent boundaries
What can the tsunami wavelength be?
200–500 km
What is the tsunami period?
10 minutes–2 hours
How fast can a tsunami travel in deep water?
435 mph
Why are tsunamis harmless to ships?
They have small amplitude in deep water
What happens as tsunamis approach shore?
Slow down and grow taller
What is a drawback in tsunami terminology?
Water receding before tsunami
What is run-up elevation?
Vertical height reached
What is inundation limit?
Horizontal distance inland
Is danger over at the inundation limit?
No
Why do tsunami waves bend around islands?
Refraction
What causes tsunami interference patterns?
Both A and B
How do tsunamis arrive?
As wave trains
What do DART stations detect?
Pressure changes on seafloor
What is the most abundant atmospheric gas?
Nitrogen
Where does weather occur?
Troposphere
What warms the stratosphere?
Ozone absorbing UV
Why is the mesosphere cold?
No ozone
Why is the thermosphere hot?
Absorbs high-energy radiation
What is weather?
Short-term
What is climate?
Long-term
Why does warm air rise?
It expands and becomes less dense
Why does cold air sink?
It contracts and becomes denser
What does relative humidity measure?
How close air is to saturation
Which air holds more water?
Warm
What causes wind?
Pressure differences
How does Coriolis affect air in the Northern Hemisphere?
Deflects to the right
When do clouds form?
When air rises and cools
What is the jet stream?
A high-altitude fast wind