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Earthquakes and Volcanoes
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Earthquakes and Volcanoes
Earthquakes and Volcanoes
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1
Question
What happens to rocks under compressive stress that deform plastically?
Answer
The rocks crumple into folds, which are bends in the rock layers.
2
Question
How do joints and faults differ in terms of rock fracture?
Answer
A joint is a fracture where blocks of rock remain stationary, while a fault is a fracture where blocks of rock move on one or both sides.
3
Question
Why are faults often reactivated multiple times?
Answer
Because plate tectonic processes continue in the same locations and faults are zones of weakness, making movement along existing faults easier than creating new ones.
4
Question
What is the relationship between plate boundaries and earthquakes?
Answer
Nearly all earthquakes occur at plate boundaries—divergent, convergent, and transform boundaries all experience earthquake activity due to movement of lithospheric plates.
5
Question
Explain the elastic rebound theory of earthquakes.
Answer
It describes how stress builds up in rocks until they rupture suddenly, releasing stored energy and causing the rocks to move and generate an earthquake.
6
Question
Differentiate between the earthquake focus and epicenter.
Answer
The focus is the point below the Earth's surface where the rupture starts, while the epicenter is the point on the Earth's surface directly above the focus.
7
Question
Why do shallow earthquakes usually cause more damage than deeper ones?
Answer
Because their focus is close to the Earth's surface where people and structures are located, causing stronger surface shaking and destruction.
8
Question
Describe the role of transform plate boundaries in earthquakes, with an example.
Answer
Transform boundaries involve plates sliding past each other horizontally, leading to shallow focus earthquakes; the San Andreas Fault in California is an example.
9
Question
What are seismic waves and how do they transmit earthquake energy?
Answer
Seismic waves are vibrations that travel through the Earth's interior and surface, carrying the energy released by an earthquake away from its focus.
10
Question
Compare body waves and surface waves in seismic activity.
Answer
Body waves travel through the Earth's interior and include P-waves (fastest) and S-waves (slower), causing sharp jolts, while surface waves travel along the ground surface and cause rolling motions, responsible for most damage.
11
Question
How does a seismograph record earthquake waves?
Answer
It uses a suspended pen attached to a stationary frame and a rotating drum connected to the ground; as the ground shakes, the drum moves beneath the still pen, creating a seismogram showing wave patterns.
12
Question
How can the earthquake epicenter be determined using seismograms?
Answer
By using at least three seismograms to calculate distances from different seismometers, drawing circles with these distances as radii, and finding the intersection point of the circles corresponding to the epicenter.
13
Question
What were the limitations of the Mercalli Intensity Scale?
Answer
It was subjective, depending on people's perceptions and local conditions, which made comparison between earthquakes difficult.
14
Question
Explain how the Richter magnitude scale quantifies earthquakes.
Answer
It measures the amplitude of the largest seismic wave logarithmically, where each whole number increase represents a tenfold increase in wave amplitude and roughly a 30-fold increase in energy released.
15
Question
Why might a high Richter magnitude not always indicate greater damage?
Answer
Because Richter measures the largest jolt, a short sharp pulse might score higher than a longer intense earthquake that releases more energy and causes more damage.
16
Question
How does the moment magnitude scale differ from the Richter scale?
Answer
The moment magnitude scale measures total energy released based on fault rupture area and movement distance, providing a more accurate magnitude; it is also logarithmic like the Richter scale.
17
Question
What factors make accurate earthquake prediction difficult?
Answer
Predictions must specify date, location, and magnitude accurately to be useful, but current science cannot reliably provide such precise forecasts, and false alarms have serious consequences.
18
Question
How and where do volcanoes generally form?
Answer
Volcanoes form where magma chambers exist beneath Earth's crust, often along convergent plate boundaries where subduction occurs, such as the Pacific Ring of Fire.
19
Question
Describe the basic mechanism of a volcanic eruption.
Answer
Magma expands due to heating and pressure underground, seeks cracks (vents), and escapes to the surface as lava or gases, resulting in an eruption that can be explosive or effusive.
20
Question
What distinguishes explosive volcanic eruptions from non-explosive ones?
Answer
Explosive eruptions occur when magma interacts with water and gases under high pressure causing violent bursts, while non-explosive eruptions involve calm lava flows with less sudden gas release.
21
Question
How does magma composition affect lava viscosity and eruption style?
Answer
High silica content increases lava viscosity, causing it to flow poorly, clog vents, trap gas, and produce explosive eruptions; low-viscosity lava flows more easily, resulting in effusive eruptions.
22
Question
What is pyroclastic material and how is it formed?
Answer
Pyroclastic material consists of solidified fragments of molten rock ejected into the air during explosive eruptions, like pumice which shows gas bubble holes from trapped gas in the lava.
23
Question
What are the three major types of low-viscosity lava and how do they differ?
Answer
A’a lava has a rough, jagged texture; pahoehoe lava is smooth and rope-like; pillow lava forms when lava extrudes underwater creating rounded, pillow-shaped formations.
24
Question
What natural features form when hot water heated by magma reaches the Earth's surface?
Answer
Hot springs and geysers form where heated water reaches the surface; geysers erupt explosively when superheated water trapped underground breaks through narrow vents.