Chapter 2 Gateway 2 Flashcards
Explain the formation of fold mountains.
Layers of rocks when compressed and folded form fold mountains. They are formed along convergent plate boundaries, where plates move along towards each other and collide. The resultant compressional force creates immense pressure, causing the layers of rocks to buckle and fold. This process is known as folding which involves the compression of rock layers to wave-like structures
Upfold → anticline, downfold → syncline.
When there is an increasing compressional force on one limb of a fold, the rocks may buckle until a fracture forms. The limb may move forward to ride over the other limb
Examples include Himalayas and Rocky Mountains.
Explain the formation of rift valley and block mountain.
Rift valleys and block mountains are formed at divergent plate boundaries, where plates are pulled apart, giving rise to fault. A fault is fracture in the rocks along which the rocks are displaced. Tensional forces from these movements result in parts of the crust being fractured. This process is known as faulting.
Sections of the crust extend along fault lines. Tensional forces can cause a central block of land to subside between a pair of parallel faults, giving rise to rift valley. Block mountain is formed between a pair of parallel faults. A block mountain is a block of land with steep stones left standing higher than the surrounding land.
For example, two block mountain, Vosges in France and the Black Forest in Germany are separated by the Rhine Valley. They are form due to the divergence of the Eurasian Plate and North American Plate.
Explain the formation of volcanoes.
A volcano is a landform formed by magma ejected from the mantle onto the earth’s surface. Magma is molten rock found below the earth’s surface and builds up within the crust to form a magma chamber. A magma chamber is a reservoir of molten rock beneath the earth’s crust.
Volcano can be found at divergent and convergent plate boundaries where there is subduction. Mantle material melts to form magma and magma rises as it is less dense than the surrounding rock. Magma accumulates in the magma chamber, where the pressure builds up until the magma forces its way onto the earth’s surface through vents. Vents are opening in the earth’s surface with a pipe leading to the magma chamber. Magma that is ejected onto the earth’s surface is known as lava which builds up around the vent to form a volcano. The upward movement of the magma both into the earth’s crust and onto the earth’s surface is known as vulcanicity.
Define ‘viscosity’ and explain the formation and impacts of lava with different viscosity.
Viscosity refers to the stickiness of the lava or its resistance to flow.
Low-silica lava has lower viscosity which result in less explosive volcanic eruptions. Low-silica lava allows gases to escape easily and flows more easily through the vent before reaching the surface. Outer layer of cooling lava forms a thin crust upon contact with the earth’s surface.
High-silica lava is more viscous and thus traps more gases more easily. This result in the build-up of pressure below the earth’s surface. Gases expand when magma rises towards the earth’s surface, causing an outward explosion. This volcanic eruption eject lava, ash, rock fragments and gases into surrounding environment
Describe the characteristics of shield volcanoes.
Shield volcanoes have gently sloping sides and a broad summit. These volcanoes are formed where low-silica lava has been ejected. Low-silica lava flows easily and spreads out over a large area before solidifying. The eruptions are not explosive since lava does not trap much gas. With each successive eruption, the base of the volcano increases in size as lava accumulates. Shield volcanoes are found near divergent plate boundary.
An example of a shield volcano is Mount Washington in the United States of America.
Describe the characteristics of stratovolcanoes.
Stratovolcanoes develop from successive eruptions of lava and pyroclasts. Pyroclasts refer to ash, rock fragments and volcanic bombs ejected during a volcanic eruption.
After the initial eruptions of pyroclasts, the subsequent eruption ejects lava which covers the pyroclasts and prevents it from being eroded away. Over time, successive eruptions build a high volcano with a slightly concave profile, which means that the volcano steeper at the top and gentler at the base. Secondary cones may develop as magma from the vent seeps into the sides of the cone and erupts
Describe how the stratovolcanoes erupt.
- As more magma seeps into the magma chamber, the amount of pressure in the chamber builds up, giving rise to a volcanic eruption.
- When a stratovolcano erupts, pyroclasts are released. The force of the volcanic eruptions depends on the amount of pressure built up within the volcano.
- A new eruption of lava covers the pyroclasts and builds up the volcano.
- Lava builds up around the vent, solidifying to form a small volcanic cone. The bowl-shaped opening is called the crater.
- During the formation of the volcano, the vent may become blocked. This forces the magma to find a new exit route to the surface. A secondary cone of newer volcanic material will then develop.
- The summit of a volcano may be blown off during an explosive eruption. The sides of the crater collapse inwards due to the loss of structural support. As a result, a large depression known as a caldera is formed.
Explain how an earthquake is formed.
Earthquake is a vibration in the earth’s crust caused by the sudden release of stored energy in the rocks found along fault lines. Due to friction between the moving plates, there is a slow build-up of stress on the rocks found on either side of the fault. When the rocks can no longer withstand the increasing stress, they can suddenly slip many metres, causing an earthquake.
Earthquake releases energy in the form of seismic waves. Seismic waves radiate out from a point of sudden energy release called the focus. The epicentre is the point on the earth’s surface directly above the focus. Most of the energy released by the earthquake travels along the surface of the earth, causing the ground to vibrate violently.
After an earthquake, stress from the ground within the earth’s crust may cause aftershocks to occur along the fault line
Compare the deep-focus earthquake and shallow-focus earthquake.
Deep-focus earthquake occurs between 70 and 700 km below the earth’s surface. Shallow-focus earthquake occurs in upper 70 km of earth’s crust.
Deep-focus earthquake have a smaller impact on the land as vibrations or seismic waves take a longer time to reach the surface. Energy lost along its way. Shallow-focus earthquake has a greater impact on land as vibrations or seismic waves reach the land surface more quickly
Explain how the damaged done by earthquake is affected by magnitude.
Earthquake release different amounts of energy. The amount of energy released is described as the magnitude of an earthquake. The Ritcher Scale is used to measure the magnitude of an earthquake. For each increasing magnitude on the Ritcher scale, the impact of the earthquake becomes 10 times greater in magnitude than the previous one.
Explain how the damaged done by earthquake is affected by population density.
Earthquakes in sparsely populated areas affect fewer peope than in densely populated areas. Therefore, an earthquake in a city cause more casualties and damage than an earthquake in the countryside.
Explain how the damaged done by earthquake is affected by level of preparedness.
Preparations include having evacuation plans, trained rescue workers and a range of action plans. The damage done by an earthquake is more manageable when people are better prepared for it.
Explain how the damaged done by earthquake is affected by distance from epicentre, with reference to examples.
The damage caused by an earthquake is more severe when an area is closer to the epicentre of the earthquake. During the earthquake in Christchurch, New Zealand in 2011, the epicentre was in a town a few kilometres away from the city centre. The city suffered more damage than areas further away from the city.
Explain how the damaged done by earthquake is affected by time of occurrence, with reference to examples.
The time of day during which the earthquake occur determines where people are and what they are doing. This will affect people’s chances of survival in an earthquake. If earthquake occurs when people are sleeping, there is a higher chance that these people will be trapped in their houses and more death will occur. For example, more than 2,400 people died when an earthquake occured a couple of hours after midnight in the Sun Moon Lake Region in Taiwan in 1999.
Explain how the damaged done by earthquake is affected by type of soil, with reference to example.
In places where the sediments are loose and unconsolidated, the seismic waves are amplified and this result in greater damage when earthquake occur. Structures build on saturated and unconsolidated sediments can be affected by liquefaction. Liquefaction is when the ground becomes unstable and saturated soil flows like a liquid. In Christchurch, many houses and buildings had to be abandoned because of liquefaction after the earthquake in 2011.
Explain how are earthquake are measured.
A seismograph records the seismic waves released by an earthquake. A spring-mounted weight in the seismograph moves up and down when tremors are detected. An ink marker then records the motions of the ground by making vertical markings on a piece of graph paper which is attached to a rotating drum.
The distance that a location shifts as a result of an earthquake is closely related to the magnitude of the earthquake. Measuring how far a location shift allows scientists to calculate the magnitude of the earthquake that has occured. The Global Positioning System can be used to measure how far a location has shifted as a result of an earthquake.
Explain how earthquake causes tsunamis, with reference to examples.
Seismic energy from an oshore earthquake forces out a mass of sea water. On reaching shallower water, greater friction slows the waves and forces the to increase in height . At the point of impact on the coast, the tsunami waves is travelling at faster speeds and greater heights. Sometimes the sea recedes from the coast before advancing onshore because water first rushes to fill the void caused by the movement of the sea floor. It only does so mintues before the tsunamis reaches the shore. Water forced out again soon afterwards, causing a tsunamis.
In 2004, a 9.2 magnitude earthquake occurred in the Indian Ocean and triggered a tsunami with waves that spread throughout the Indian Ocean. The tsunami caused damage to coastal communities in 12 countries, most damaged being Sumatra, Indonesia.
Explain how earthquake causes disruption of services, with reference to examples.
Earthquake disrupts services such as the supply of electricity, gas and water, potentially affecting a large area. Vibration on the ground can snap pipes and break cables which may cause outbreak of fires. Communication services such as television broadcasts and telephone connections may also be affected. The earthquake in Kobe, Japan, in 1995, damaged pipes and transimission lines. This disrupts electricity, gas and water supplies to about a million of Kobe city’s 1.4 million residents.
Explain how earthquake result in landslides, with reference to examples.
Shaking of ground during earthquakes can weaken the slopes of hills and mountains. The unstable slopes result in landslides. Thus, there is rapid downward movements of soil, rock and vegetation debris from a slope. In 1970, an earthquake off the coast of Peru destabilised the slope of Mount Huascarán and triggered a massive landslide. The landslide travelled at more than 160 km/h and completely flatten the town of Ranrahirca within seconds. The death troll was more than 18,000 and only 200 people survive the disaster. Mudflows may also occur when there is heavy rainfall, which saturates the soil, causing the mixed soil debris to flow down the slope.
Explain how earthquake result in destruction of properties, with reference to examples.
Earthquakes can cause widespread destruction to many homes. People may be without homes after the disaster and reside at temporary shelters while their homes are being rebuilt. The earthquake in Tohoku, Japan, in 2011 caused a tsunami which travelled up to 10 km inland. Extensive structural damage results in hundreds of thousands of people being forced from their homes. There was a severe shortage of housing and concerns about a long-term consequences on the health of the people.
Explain how earthquke can cause destruction of infrastructure, with reference to examples.
Earthquake may cause cracks to form in the infrastructure such as roads and bridges. Transportation can be disrupted as it is unsafe to use the damaged road. For example, after the earthquake in Kobe, Japan, many places in the city become inaccessible or difficult to reach. Japan’s total cost of repair after the earthquake in tohoku was US$300 billion. This amount wold have be much greater if not for the enforcement of building codes in Japan, which resulted in less damage to infrastructure.
Explain how earthquake result in loss of lives, with reference to examples.
Earthquake and their associated hazards often threatens the lives of those livong in those earthquake zones. In SiChuan, China, on May 2008, a 7.9 magnitude earthquake occurred. The estimated number of death was 100,000 and 374,000 people was injured.
State and define the three types of volcanoes present.
Active volcanoes refers to volcanoes which are currently erupting or are expected to erupt in the near future. Dormant volcanoes are currently inactive but may erupt in the future. Extinct volcano refers to volcanoes without current seismic activities and no geological evidence of eruption for the past thousand of years.
Explain how massive destruction by volcanic materials is a risk of living near volcanoes, with reference to examples.
Volcanic materials produced by volcanic eruptions include lava and pyroclastic that consists of ash, rock fragments and volcanic bombs. This volcanic materials can lead to widespread damage of property. The lava has high temperatures are between 500 degrees Celsius and 1400 degrees Celsius and burned the area it flow through. Low silica lava move rapidly and flow over long distances, causing damage to larger areas. A pyroclastic flow can destroy everything in its path with hot rock fragment ranging from ash to boulders traveling at a speed greater than 200 m/s. Inhaling the hot ash and gases can result in serious injury or death. Vocanic bomb of heated rocks can fall in areas surrounding the volcano and cause damage to property. The eruption of Nevado del Ruiz in the Andes mountains of South America in 1985 released a pyroclasts and glacial ice along its path triggered lahars. Lahars are flow of wet volcanic debris on the side of the volcano. The lahar engulfed the town of Armero and killed more than 20,000 people.
