Option D Flashcards
(73 cards)
1
Q
The internal structure of the earth
A
Crust
- Continental crust
- Oceanic crust
- On the outside is a very thin rigid crust it is composed from two parts:
- Continental crust – Thicker (20-60km), found under land masses or continents. It is generally older than oceanic crust and is less often destroyed.
- Oceanic crust – Thinner (5km), found underneath the oceans. It is denser than continental crust and can besubducted.
Mantle
Has properties of a solid but can flow very slowly
Makes up 82% of the volume of earth.
Outer core
Made from liquid nickel and iron
Inner core
Made from solid nickel and iron
2
Q
Density of the layers is controlled by two things:
A
- Pressure
2. Temperature
3
Q
Lithosphere
A
Rigid outer later that is made up of the crust and the top part of the mantle.
4
Q
Radiogenic
A
(radioactive decay of materials in the mantle and crust )
5
Q
Primordial heat
A
(heat lost by the earth as it continues to cool from its original formation)
6
Q
How is the heat transported?
A
- Conduction Main heat lost through the crust
- Convection - Main source of internal heat with the rest mainly originating in the crust Main heat transfer
- Volcanic advection - only 1% - heat transfer through liquid
7
Q
Advection
A
Is a lateral or horizontal transfer of mass, heat or other property
8
Q
Large scale convection currents:
-Large scale convection currents occur in the earth interior
A
- The inner core heats up magma at the bottom of the outer core
- Magma rises from the core to the surface
- It then spreads out at mid-ocean ridges
- The cold solidifies crust sinks back into the earth’s interior because it is heavier and denser than the surrounding material.
- The CAUSE of the movement is radioactive decay of uranium and potassium in the mantel.
9
Q
Subduction
A
Refers to the plunging of one plate beneath another.
10
Q
Formation of subduction zones:
A
Lithosphere plate colliders with either a Continental OR Oceanic plate
Subduction zones form where an oceanic lithospheric plate collides with another plate – can be continental or oceanic. The density of the oceanic plate is similar to the asthenosphere; thus it can be easily pushed down into the upper mantle.
The sub-ducted oceanic crust remains cooler and therefore denser then the surrounding mantle for millions of years thus the subduction will carry on. The subducting plate drags or pulls the rest of the plate behind it. Plates are hot at the mid-ocean ridge but cool as they move away.
11
Q
Rifting:
A
Where does it occur: Constructive plate boundaries, where the lithosphere is being pulled apart.
Cause: Hotspot activity is believed to be the main cause of rifting.
The rift valleys created consist of rock that is hotter and less dense than the older colder plate. Hot material wells up beneath the ridges to fill the gasps created by the spreading plate.
12
Q
Plate margin
A
the region where two or more plate tectonics meet. It is a zone of intense seismic activity.
13
Q
Types of plate boundaries
A
- Destructive (convergent)
- Collision
- Constructive (Divergent)
- cONSERVATIVE
14
Q
Destructive plate margin (Convergent)
A
Involves an oceanic plate and a continental plate.
- The plates move towards one another; this can cause earthquakes.
- The plates collide
- The oceanic plate is forced beneath the continental plate. This is subduction. This happens because the oceanic plate is denser (heavier) than the continental plate.
- When the oceanic late sinks into the mantle it melts to form magma.
- The pressure of the magma builds up beneath the earth’s surface.
- The magma escapes through weaknesses in the rock and rises up through a composite volcano. (eruptions are often violent, with lots of steam, gash and ash)
15
Q
Collision margin
A
When two continental plates collide neither can sink and so the land buckles up to form fold mountains. This Is called a collision margin.
*Earthquakes occur here
16
Q
Constructive plate boundaries (Divergent
A
- Two plates move apart from one another
- Magma from the mantle rises up to fill the gap (constructing new land)
- This causes shield volcanoes (don’t erupt with force as the magma can escape easily)
*Both earthquakes and volcanoes are found here.
Example- Mid-Atlantic Ridge
17
Q
Conservative plate margins (Transform)
A
- The plates move past each other or are side by side moving at different speeds.
- As the plates move, friction occurs and the plates become stuck.
- Pressure builds up because the plates are still trying to move.
- When pressure is released, it sends out huge amounts of energy, causing an earthquake.
- Earthquakes at conservative plate boundaries are very destructive because they are close to the surface
- There are no volcanos at a conservative plate margin.
Example- San Andreas Fault
18
Q
Speed of onset-
A
is how quickly the peak of the hazard event occurs, with the starting time at the first point of the process towards it becoming a hazard.
19
Q
Frequency-
A
refers to the number of hazard events in a given period of time
20
Q
Duration
A
is how long the hazard event lasts.
21
Q
Magma plumes
A
A column of hot rock rising through the mantle. The heat form the plume causes the rock to melt. . The lower lithosphere rocks are heated by theplumesand melt to form hot spots.
22
Q
Hot spot-
A
A proportion of the earth’s surface which experience volcanism.
23
Q
The types of volcanoes
A
Three most common types of volcanoes:
¬ Shield
¬ Composite
¬ Cinder
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Q
- SHIELD VOLCANOES
A
Formation: Shield volcanoes formed from very hot, runny basaltic lava. The lava is hot thus is can flow great distances therefore building up shield volcanoes.
Features: Gently sloping sides, a shallow crater and a large circumference. No explosive activity due to how they are built so no ejected fragments.
Plate boundary- constructive
Explosions: Not destructive
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2. COMPOSITE / STRATO
-Most common type of volcano
Formation: Formed by alternating eruptions of fragment material followed by lava outflow.
Features: Characterized by slopes by 3 degrees near the summit and 5 degrees near the base. The highest volcano in the word is composite. Steep-sided and cone shaped. Made up of ash and lava which doesn’t flow every far.
The main cone consists of layers of ash and lava fed from the main pipe which accumulates in the crater. Large explosions form due to cooled lava in the pipe which leads to gas build up,may blow the top off the cone and from a larger crater within which a secondary cone may develop. Frequently parasitic cones grow on the sides.
Explosions: Very destructive and violet: The pipe becomes plugged with cooled lava, the pressure of gas builds up and the result is a violent explosion.
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3.CINDER VOLCANO
Formation: Formed by fragments of solid material which accumulate as a steep conical hill around the vent to form a cone.
Features: The shape depends on the nature of the material. It is usually concave and the material spreads out near the base and has a very steep angle of 30-40 degrees depending on the size of the material. Cinder and ash cones are not usually as high (300m)
Explosions: violent eruptions, lava is ejected into the atmosphere and breaks up into cinders, ash and other fragments.
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Volcanoes are categorized on how active they are
Active- erupt frequently
Dormant – Temporarily inactive but not fully extinct
Extinct- Never likely to erupt again
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Eruptions are categorized into two main groups:
1) Lava eruptions
| 2) Pyroclastic eruptions
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Lava eruptions
The amount of silica in a lava eruption is what makes the difference between the volcanoes in Iceland and Hawaii (erupt frequently) and those in Japan and the Philippines (infrequent eruptions but violent).
Lava released where the oceans meet the continents absorb silica-rich sediments. This causes the lava to become more viscous and block the vents until enough pressure has built up to break them open.
Icelandic lava eruptions
• Persistent fissure eruptions
• Large qualities of basaltic lava may build up vast horizontal plaines.
Hawaiian eruptions
• Have a central vent
• Occasional pyroclastic activity occurs
• Runny basaltic lava flows down the sides of the volcano and gases escape easily
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Pyroclastic eruptions:
Stombolian eruptions
• explosive eruptions that produce pyroclastic rock.
• Eruptions are commonly marked by a white cloud of steam emitted from the crater.
• Frequent gas explosions blast quantities of runny lava into the air, and then these settle and cool to form a cone.
Vulcanian eruptions
• violent eruptions
• occur when the pressure of trapped gases in viscous magma becomes sufficient to blow off the overlaying crust of solidified lava.
• eruptions clear a blocked vent and spews large quantities of of volcanic ash into the atmosphere.
• Violent gas explosions blast out plunges of sticky or cooled lava.
• Fragments build up the cone of ash and pumice.
Vesuvian eruptions
• very powerful blasts of gas that push ash clouds high into the sky.
• Lava flows also occur. Ash falls to cover the surrounding area.
Plinian eruptions
• extremely violent eruptions
• huge clouds of pilcerised rock and ash (kms thick)
• Huge explosions caused when gas rushes up through the sticky lava and blasts ash and fragments into the sky.
• Gas clouds and lava rush down the slopes.
• Part of the volcano may be blast away
Pelean eruptions
• Large quantities of viscous magma are erupted
• Form glowing ash associated with pyroclastic flows
• Produce steep sided conical volcanoes
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Primary effect:
Hazards which are a direct result of the volcanic eruption (disaster)
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Secondary effect:
Hazards which are a consequences of the primary effect
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Primary effects of volcanos
Lava flows
Layers of molten lava can destroy almost everything on their path,
Pyroclastic flows
Fast moving avalanche of volcanic material including hot ash, lava fragments (pumice) and gases ejected
Tephra
-Rock fragments and particles ejected by a volcanic eruption
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Volcanic gas
Variety of dangerous gases emitted:
-Hydrogen supplied
-CO2
CO (carbon monoxide)
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Secondary hazards of volcano
Landslides
Large masses of rock and soil that fall, slide or flow very rapidly under the force of gravity.
Tsunami
A long high wave caused by an earthquake or other disturbance.
Lahars
Violent type of mudflow caused by ash erupting and mixing with river water.
Flooding
Melting glaciers / ice caps can release huge quantities of water in short periods
Climate change
Large volumes of ash ejected
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Epicenter
A point on the earth’s surface directly /vertically above the focus, point in the crust where a seismic rupture begins.
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Focus
The point inside the crust where the pressure is released is called the focus.
Earthquake energy is released in seismic waves. These waves spread out from the focus. The waves are felt most strongly at the epicenter, becoming less strong as they travel further away.
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Seismic waves
An elastic wave generated by an impulse such as an earthquake or an explosion.
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How are earthquakes recorded
The power of an earthquake is measured using a seismometer. A seismometer detects the vibrations caused by an earthquake. It plots these vibrations on a seismograph.
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Body waves
Waves that travel within the earth (P and S)
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Surface Waves
Waves that travel on the surface. They are slower moving than body waves but must larger thus more destructivity only travel through solid media.
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Body waves-
P-waves (Primary waves)
- Move back and forth
- Waves that cause the ground to compress and expand (move back and forth in the direction of travel)
- Compressional wave caused by the movement of two plates that travel through the body of the earth to the surface.
- First waves plotted on the seismograph.
- This wave travels the quickest.
- Travels through solid, liquid and gases (speed decreases when it changes state from solid to liquid)
-Cause the least harm to environment.
S-waves (Secondary waves)
- Sideways and up and down (Transverse) wave that shake the ground in a motion that is perpendicular to the direction of travel.
- Move the ground horizontally = damage
- They always arrive after P waves at seismic recordings
- Only travel through solids
- Horizontal movement of the ground can cause damage
- Moderate speed
- Shadow zones: Places where secondary waves occur
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Surface waves
Body waves travel from the focus to the epicenter…
When P and S ways meet the surface they transform into:
Love waves (Surface waves)
- Cause the ground to move sideways
- Out of the two surface waves love waves move faster.
- Only pass through solid media.
Rayleigh (Surface waves)
- Cause the ground to shape in an elliptical patter (like ocean waves) up and down
- Spread of the most of all the waves thus giving them a long duration on seismograph recordings
Surface ways have a slower speed = they cause the most damage…
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The size of the earthquake depends upon the thickness of the descending slab and the rate of movement.
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How human activities cause earthquakes:
Human activity’s cause many earthquakes to occur a long way from any plate boundary…
Construction of large dams
The extra water pressure created in the micro cracks and fissures in the ground under or near the reservoir. When the pressure of the water in the rocks increase it acts to lubricate faults which are already under tectonic strain, but are prevented from slipping by the friction of the rock surfaces.
Mining
Removal of millions of tons of rock alters and puts stress on the remaining rock
Testing of nuclear weapons
Releases a lot of energy in the immediate region
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Fracking
Fracking (hydraulic fracturing) –is a process in which water containing certain chemicals is injected at very high pressure into rocks in order to open up their pore spaces and release natural gas contained within the rocks. – lead to an earthquake in Canada, magnitude of 4.4
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Fracking (hydraulic fracturing
is a process in which water containing certain chemicals is injected at very high pressure into rocks in order to open up their pore spaces and release natural gas contained within the rocks. – lead to an earthquake in Canada, magnitude of 4.4
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Hazzard
A threat (natural or human) that has the potential to cause loss of life, injury, property damage, socio-economic disruption or environmental degradation.
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Hazzard event
The occurrence of a hazard, the effects of which change demographic, economic and environmental conditions.
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Primary effects of earthquakes
Ground shaking
Result of the passage of seismic waves through the ground
Ground rupture
When an earthquake moves along a fault and breaks the earth’s surface.(very rare)
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Secondary effects of earthquakes
Tsunamis
Series of water waves caused when the seafloor moves vertically
Liquefaction and subsidence (sinking) of the ground
Liquefaction is when sediment grains are literally made to float in groundwater, which causes the soil to lose its solidity. Subsidence can then follow and the soil recompacts.
Landslides
A collapse of a mass of earth or rock from a mountain or cliff
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Impacts of earthquakes
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Impacts:
• Loss of life
• Destruction of buildings
• Interruption of water supplies
• Breakup of sewage disposal systems
• Release of hazardous material
• Fires
• Spread of chronic illness due to lack of sanitary conditions
• Floods due to collapsed dams
• Loss of public utilities such as electricity
• Business are destroyed
• High rebuilding costs
• Damage and loss of transport
• Natural and human landmarks will be lost
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Mass movement
include any large-scale movement of the earth’s surface that are not accompanied by a moving agent such as a river, glacier or ocean wave
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Types of mass movement
- Soil creep, very slow movements
- Avalanches, fast movements
- Rock falls, dry movement
- Mudflows, very fluid movement
- Landslide
- Slumping
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Safety factor
likelihood of a slope falling – relative strength or resistance of a slope compared to the force acting on it.
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Slope failure is caused by two factors:
• A reduction in the internal resistance or shear strength of the slope.
• An increase in shear stress – that is, the forces attempting to a pull a mass downslope.
Both can occur at the same time
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Shear strength
Reduction in internal strength
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Shear stress
Forces trying to pull the material down
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Causes of mass movement due to human actions
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Deforestation
Construction of roads
Irrigation
Mining
Building on steep gradient
Agriculture
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Spatial distribution
is the arrangement of a phenomenon across the Earth's surface and a graphical display of such an arrangement is an important tool in geographical and environmental statistics.
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Where do earthquakes occur?
Most earthquakes occur along the edge of the oceanic and continental plates. The earth's crust (the outer layer of the planet) is made up of several pieces, called plates. The plates under the oceans are called oceanic plates and the rest are continental plates.
Collision plate margin
Constructive plate margin
Destructive plate margin
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Where do volcanoes occur?
Where do volcanoes occur?
There are three main places where volcanoes originate:
• Hot spots - not a plate boundary
• Divergent plate boundaries (such as rifts and mid-ocean ridges)
• Convergent plate boundaries (subduction zones)
Sixty percent of all active volcanoes occur at the boundaries between tectonic plates
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The Ring Of Fire
The ring of fire is a major area in the basin of the Pacific ocean where many earthquakes and volcanic eruptions occur.
It is a very active area as it consists of most of the earths 3 main subduction zones.
1. Eurasian plate
2. Pacific plate
3. Indo-Australian plate
Roughly 90% of all earthquakes occur along the ring of fire.
Ring is dotted with 75% of all active volcanoes on earth (452 volcanoes in total).
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Hotspot volcanoes
The vast majority of volcanic activity occurs where tectonic plates collide, called convergent boundaries, or spread, called divergent boundaries. However, there is a special class of volcanoes that form within plates.
These inter-plate volcanoes are known as hotspot volcanoes. Hotspot volcanoes that form under continental plates are called super volcanoes, representing the most powerful and violent volcanoes on Earth.
• Don’t occur at plate boundary’s but under them.
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How to manage earthquakes:
Prediction:
Seismic preparedness using using seismic zonation maps to predict earthquakes.
Prediction – use seismometers
Management:
• Increase communication sources
- Phone updates - Every smartphone in Japan is installed with an earthquake and tsunami emergency alert system. Triggered around five to ten seconds prior to the impending disasters, it’s meant to give users time to quickly seek protection if necessary. The system chants “Jishin desu! Jishin desu!” (translating to “There is an earthquake”) until the earthquake stops.
• Have distinguished open assembly area
• Transportation
- Bullet train to evacuate individuals
• Implement building codes for engineered structures
- They use rubber to absorbs shock/ steel frames/ deep foundations to absorb seismic waves
• Evacuation plans/drills and public education
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How to manage landslides:
Prediction:
They use multiple factors and combine them to make a world map of risk in relation to landslides.
-Use rainfall data from the global precipitation measurement core observatory (GPM) to analysis risk.
-They look at faults in the earth
-Deforestation and construction
-Nature of geology in that area
Data is combined to create a map of precipitation which shows which are the most venerable
Management:
* Trees should be planted
* Modify slop geometry
* Use chemical agents to reinforce slop material
* Installing structures such as piles and retaining walls
* Diverting debris pathways
* Rerouting surface and underwater drainage
* Created a website to share information – reports submitted by the public to make the info more accurate – landslides.nasa.gov
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How to manage volcanos:
Volcanoes
Prediction:
Use gases to determine behavior of volcano
Sulphur dioxide emissions rise and fall with the activity of the volcano as its emitted close to the surface – measured using an ultra-violent spectrometer.
Management:
• Stay indoors until the ash settles
• Wear masks and goggles to create a barrier between sources emitted from the volcano
• Public education
• Establish evacuation centers, routes and logistics.
• Put out information on TV, radio or if need be personal contact.
• Volcano monitoring
• Relocation
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Recurrence interval / return period
Is the expected frequency of occurrence in years for an event of a particular size
High frequency occurrence = low magnitude
Low frequency occurrence = high magnitude
The larger the magnitude of events cause the most damage and therefore require the greatest management.
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Richter scale:
What is it?
Is a scale of numbers used to tell the power / magnitude of earthquakes
How does it work?
It is measured using a machine called a seismometer which produces a seismograph.
The earthquakes magnitude is determined using the logarithm of the amplitude (height) of the largest seismic wave calibrated to a scale by a seismograph.
The Richter scale is normally numbered 1-10. It is a logarithmic scale. Earthquakes measuring 1-2 on the scale are common and they are so minor that people cannot feel them. Earthquakes measuring upwards of 7 are less frequent but very powerful and can cause a lot of destruction.
Earthquakes are above 8 on the Richter scale tend to occur once a year on average. Whereas earthquakes below 5 occur thousands if not millions of times a year globally:
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Moment Magnitude scale (M) / Moment magnitude scale
What is it?
quantitative measure of an earthquake's magnitude
How does it work?
Calculations of an earthquake’s size using the moment magnitude scale are tied to an earthquake’s seismic moment (M0) rather than to the amplitudes of seismic waves recorded by seismographs. The moment magnitude scale is the only scale capable of reliably measuring the magnitudes of the largest, most destructive earthquakes (that is, greater than magnitude 8).
The Richter scale is not very accurate in measuring these larger earthquakes and today scientists use the Moment Magnitude Scale which uses the same logarithmic scale but which more accurately measures the strength of larger earthquakes.
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Mercalli scale
What is it?
is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake?
How does it work?
Categorizes earthquakes into 12 different categories. designed to describe the effects of an earthquake, at a given place, on natural features, on industrial installations and on human beings. The intensity differs from the magnitude which is related to the energy released by an earthquake.
How does it differ?
Unlike with the Richter scale, the Mercalli scale does not take into account energy of an earthquake directly. Rather, they classify earthquakes by the effects they have (and the destruction they cause). When there is little damage, the scale describes how people felt the earthquake, or how many people felt it.
Very often, non-geologists use this scale, because it is easier for people to describe what damage an earthquake caused, than to do calculations to get a value on the Richter scale.
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Volcanic Eruption Index.
What is it?
The strength of a volcano is measured by the Volcanic Eruption Index
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How does it work?
This is based on the amount of:
1. material ejected in the explosion
2. the height of the clouds it creates
3. amount of damage caused
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- Basalt eruptions are between 0-3
- Andesite eruptions are between 4-7
*The larger the VEI value, the larger the eruption
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Measuring landslides:
How does it work?
measured by extensometer, inclinometer or GPS (global positioning system).
This equipment’s are measuring some points or along the lines; it is difficult to measure the whole landslide area.
extensometer - is an instrument used to measure the movement of cracks on unstable rock slopes
inclinometer - is an instrument used for measuring angles of slope
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Risk calculation
Risk = Hazard + Vulnerability
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Post natural hazard
| The 3 Rs:
1) Relief (Phase1)
- The relief cycle tarts straight away.
- During the first few hours and days efforts are made to provide food, water, clothing, shelter and medical care to all inhabitants of the affected area, and to stop continued loss and disruption directly related to the event (such as the collapse of damaged buildings, or the spread of fire or infectious disease).
- Relies on speed and efficiency.
- Mistakes can be made despite efforts to make rational decisions in the face of panic reactions and lack of time, resources and full information and understanding.
- Relief teams from outside the immediate area may arrive to help or organize search, rescue and care operations.
- Urgent supplies of medical drugs and equipment, rescue equipment, clothing and food may be flown in;
- International relief agencies such as the Red cross provide vital logistical, medical and humanitarian support during this critical initial phase of disaster response.
2) Rehabilitation (phase 2)
- Lasts several weeks or months
- Actions are designed to restore physical and community structures to at least a temporary return to normality
- Mass shelter is replaced by temporary housing, the injured are transferred from field hospitals to regular hospitals, money and resources are made available to the unemployed and dispossessed.
- - rehabilitation requires accurate assessment of needs and carefully coordinated planning of responses
- - The risk of recurrent disasters commonly remains during this phase - if the hazard strikes again
- Rehabilitation efforts are normally planned and executed locally
3) Reconstruction (phase 3)
- when permanent changes are introduced to restore the quality of life and economic stability to at least its original level or improve on the past by creating better economic opportunities and a higher quality of life.
