Why are Some Areas at More Risk of Tectonic Hazards? Flashcards
(41 cards)
What is a hazard and what are its types?
A hazard is a potential threat to human life and property.
There are two types of natural hazards:
Hydro-meteorological hazards: Caused by climatic processes.
Geophysical hazards: Caused by land processes.
Where do geophysical hazards typically occur, and what causes them?
Geophysical hazards usually occur near plate boundaries.
Plates move at different speeds and directions, causing collisions, earthquakes, and volcanic activity.
Earthquakes can also occur away from plate boundaries (intraplate) due to pre-existing weaknesses in the plates that become reactivated, forming seismic waves.
What is a volcanic hotspot and where are they located?
A volcanic hotspot is a localized area of the lithosphere with unusually high temperature due to upwelling of hot molten material from the Earth’s core.
Hotspots are often found at the center of plates, such as the Hawaii hotspot.
What is the process that occurs at volcanic hotspots and what are examples of regions affected?
At hotspots, magma rises as a plume (hot rock) from the Earth’s mantle.
An example of a hotspot is the Ring of Fire, located around the Pacific Ocean.
What are the Oceanic and Continental Fracture Zones (OFZ and CFZ)?
The Oceanic Fracture Zone (OFZ) is a belt of tectonic activity through oceans and along mid-ocean ridges, passing through regions like Africa, the Red Sea, and the Dead Sea.
The Continental Fracture Zone (CFZ) is a belt of activity along mountain ranges, from Spain through the Alps to the Middle East and Himalayas.
What trends have been observed in tectonic hazards since 1960?
The total number of recorded hazards has increased.
The number of fatalities has decreased overall, though there are spikes during mega disasters.
The number of people affected by tectonic hazards has increased due to population growth.
The economic costs of hazards and disasters have risen significantly due to increased development, more expensive infrastructure, and a higher number of insurance policies, especially in developed countries
Why is reporting disaster impacts difficult?
Reporting is difficult due to several factors:
Deciding whether to count direct deaths or indirect deaths (e.g., from diseases spread after the disaster).
Challenges in accessing rural and isolated areas, making data collection hard.
Different methods used by organizations, leading to conflicting reports.
Potential bias in government-reported deaths, as seen in the 2004 Indian Ocean tsunami when the Burmese government reported zero deaths, likely due to political reasons.
What are the four main sections of the Earth?
The Earth consists of the crust, mantle, outer core, and inner core.
What is the crust, and what are its characteristics?
The crust, also known as the lithosphere, is the Earth’s uppermost layer.
It is the thinnest, least dense, and lightest layer.
Oceanic crust is only 7 km thick, while continental crust can be up to 70 km thick.
What is the mantle, and what are its key features?
The mantle, also called the asthenosphere, lies below the crust.
It is largely composed of silicate rocks rich in iron and magnesium.
The mantle is semi-molten, and convection currents within it are generated by a temperature gradient towards the core.
These convection currents may contribute to the movement of tectonic plates.
The mantle extends from 700 km to 2890 km below the Earth’s crust.
What is the outer core, and where is it located?
The outer core consists of dense, semi-molten rocks containing iron and nickel alloys.
It is located between 2890 km and 5150 km below the Earth’s surface.
What is the inner core, and what is its composition?
The inner core has a similar composition to the outer core, consisting mainly of iron and nickel.
It is located over 5150 km below the Earth’s crust.
The inner core is solid due to the extreme pressures it experiences.
The high temperature of the core results from:
Primordial heat left over from the Earth’s formation.
Radiogenic heat produced from radioactive decay.
What are the three types of plate boundaries and how do plates move?
Plates can move in three ways:
Destructive Plate Margins: Plates move towards each other.
Constructive Plate Margins: Plates move away from each other.
Conservative Plate Margins: Plates move parallel to each other.
What happens at destructive plate boundaries between oceanic and continental plates?
The denser oceanic plate subducts beneath the continental plate.
A deep ocean trench is formed where the oceanic plate subducts.
The subducted oceanic crust is melted in the asthenosphere.
The pressure caused by the molten magma builds up.
The pressurized magma forces through weak areas in the continental plate, resulting in explosive, high-pressure volcanoes known as composite volcanoes.
Fold mountains are formed as sediment is pushed upwards during subduction.
What happens at destructive plate boundaries between oceanic and oceanic plates?
The heavier oceanic plate subducts beneath the other, forming an ocean trench.
The built-up pressure causes underwater volcanoes to erupt through the oceanic plate.
Lava cools and forms new land, creating island arcs.
What happens at destructive plate boundaries between continental and continental plates?
Both plates are less dense than oceanic plates, so a lot of pressure builds up.
Ancient oceanic crust is subducted slightly, but continental crust is not subducted.
The pressure causes a pile-up of continental crust on top of the lithosphere.
Fold mountains are formed from the accumulation of continental crust.
What happens at constructive plate boundaries between oceanic plates?
Magma rises to fill the gap left by the two separating oceanic plates, forming new land when it cools.
Less explosive underwater volcanoes are formed as the magma rises.
The process of new land forming on the ocean floor is known as sea floor spreading, where the floor spreads and gets wider.
What is the evidence for seafloor spreading?
Seafloor spreading, theorized by Harry Hess in the 1940s, is supported by the study of paleomagnetism.
Paleomagnetism studies the magnetic fields of rocks. As new rocks form and cool at plate boundaries, the magnetic grains align with the Earth’s magnetic poles.
Since Earth’s poles switch periodically, new rocks formed at plate boundaries align in the opposite direction to older rocks.
Symmetrical bands of rock with alternating magnetic polarity on either side of constructive plate boundaries provide evidence for seafloor spreading.
What happens at constructive plate boundaries between continental plates?
As plates separate, land in the middle of the gap is forced apart, creating a rift valley.
Volcanoes form where magma rises to the surface.
Over time, the rift may fill with water, separating completely from the main landmass.
The raised areas of rocks are called horsts, while the valley itself is called a graben.
What forces influence how convergent plate boundaries occur?
Ridge Push: The slope created when plates move apart causes gravity to act on the plates, pushing them further apart (also known as gravitational sliding).
Slab Pull: When a plate subducts, the plate sinking into the mantle pulls the rest of the plate with it, further driving subduction.
What is a conservative plate boundary, and what occurs there?
At a conservative plate boundary, plates move parallel to each other in different directions or at different speeds.
No plates are destroyed, so no landforms are created.
Pressure builds up as the plates move, potentially displacing large amounts of water on oceanic crust or creating fault lines on continental crust.
What are the differences between oceanic and continental crust?
Oceanic crust: Has a high density, mainly made of basalt, is thin, and is newly created.
Continental crust: Has a low density, mainly made of granite, is thick, and is older.
How does the density of a plate determine its behavior at plate boundaries?
The density of a plate determines whether it subducts or is forced upwards.
This determines the landscape features and the hazards the margin is vulnerable to.
What are the different mechanisms that cause plate movement?
Mantle Convection: Radioactive decay in the Earth’s core generates thermal energy, causing the lower mantle to heat up and rise. As the magma rises, it cools, becomes denser, and sinks back down, creating convection currents that push the plates.
Slab Pull: Old oceanic crust, being the most dense, submerges into the mantle, pulling the rest of the plate with it. This mechanism, theorized by Dan McKenzie, is considered the primary cause of plate movement.
