Chapter 1 Gateway 2: Rift Valley And Fold Mountains Flashcards
How are fold mountains formed?
Over millions of years, layers of rocks when compressed and folded
What are examples of fold mountains?
- The Himalayas
- Rocky Mountains
- The Andes
What is folding?
The process by which the resultant compressional force creates immense pressure which causes the layers of rocks to fold and buckle
Upfold
Downfold
Anticline
Syncline
Description of the formation of the Himalayas
For example, the Himalayas, which span across Southern Asia, were formed when the northward-driving Indian plate collide with the Eurasian plate
Description of the formation of the Rocky Mountains
The Rocky Mountains, located in North America, are another example of fold mountains. They are formed from the almost complete subduction of the Juan de fuca plate beneath the North American plate
Where are rift valleys and block mountains formed?
Divergent plate boundaries
Sedimentary rocks
Formed from multiple layers of sediments
Igneous rocks
Formed when molten rocks cool and solidify
Matamorphic rocks
Formed when rocks are changed by high temperature or pressure within the crust
What is a fault?
A fracture in the rocks along which the rocks are displaced
What is faulting?
The process by which the tensional forces from these movements result in parts of the crust being fractured
What is a Rift Valley?
A valley with steep sides
Rift Valley formation
Convection currents drag the continental plates above it and cause it to diverge. Due to tensional forces, they are stretched and faults are formed at the plate boundary. When sections of the crust extend along fault lines, the central block of land subsides forming a linear depression know as a rift valley
What is a block mountain?
A block of land with steep slopes left standing higher than the surrounding land
Block mountain formation
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What is a volcano?
A landform formed by magma ejected from the mantle onto the earth’s surface
What is a magma chamber? How is it formed?
A reservoir of molten rock beneath the earth’s crust
Magma is molten rock found below the earth’s surface and builds up within the crust to form a magma chamber
What are vents?
Openings in the earth’s surface with a pipe leading to the magma chamber
What is vulcanicity?
The upward movement of the magma both into the earth’s crust and onto the earth’s surface
Formation of volcano (general)
Volcanoes can be found at divergent plate boundaries and convergent plate boundaries where there is subduction. At these subduction zones, mantle material melts, forming magma. Magma rises as it is less dense than the surrounding rock. It then accumulates in the magma chamber, where pressure builds up until the magma forces it’s way up onto the earth’s surface through vents. The lava builds up around the vent to form a volcano.
What are the characteristics of volcanoes?
- Vary in shape and size due to the characteristics of the lava
- Low-silica lava —> low viscosity
- High-silica lava —> high viscosity
What is viscosity?
The stickiness of the lava or it’s resistance to flow
What are the types of volcanoes?
- Shield volcanoes
2. Stratovolcanoes
What is an earthquake? (Definition, occur, formation, energy released)
DEFINITION
An vibration in the earth’s crust caused by the sudden release of stored energy in the rocks along fault lines
OCCUR
When there is plate movement along plate boundaries
FORMATION
Due to friction between the moving plates, plates movements cause the 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 slip many metres, causing an earthquake
ENERGY RELEASED
Seismic waves
What is focus, epicentre and aftershocks?
FOCUS wait EPICENTRE The point on the earth’s surface directly above the focus AFTERSHOCKS Many smaller earthquakes
What are the types of earthquakes?
- Deep-focus earthquake
2. Shallow-focus earthquake
Deep-focus earthquake
LOCATION
Occurs between 70 and 700 kilometres below the earth’s surface
IMPACT
Smaller impact on the land surface as vibrations or seismic waves take a longer time to reach the surface and would have lost most of their energy by then
Shallow-focus earthquake
LOCATION
Occurs in the upper 70 kilometres of the earth’s crust
IMPACT
Greater impact on the land as vibrations or seismic waves reach the surface more quickly
What is the richter scale?(definition,increasing magnitude)
DEFINITION
Used to measure the magnitude of an earthquake
For each increasing magnitude, the impact of the earthquake becomes 10 times greater
Shield volcano and stratovolcano
SHIELD Low-silica lava Low viscosity Less explosive Short Divergent plate boundaries EXP: Mount Washington in the united states of america STRATO High-silica lava High viscosity Explosive Tall EXP: Mount Pinatubo in the Philippines
Extent of earthquakes
- Magnitude
- Population density
- Level of preparedness
- Distance from epicentre
Magnitude
Magnitude is the amount of energy released in during an earthquake and is measured using the richter scale. For each increasing magnitude on the richter scale, the impact of the earthquake becomes 10 times greater than the previous one
Population density
The number of people living in the affected area is an important factor. Earthquakes in sparsely populated areas are likely to affect lesser people than in densely populated areas
Level of preparedness
The amount of preparation taken by the authorities and citizens makes a significant difference to the impact of an earthquake. These preparations include evacuation plans. The damage caused by an earthquake is more manageable when people are prepared for it.
Distance from epicentre
The damage caused by an earthquake is more severe when an area is closer to the epicentre of an earthquake
Time of occurrence and type of soil yk
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Tsunami
An unusually large sea wave
The movement of the sea floor during a large earthquake at the subduction zones
An explosive underwater volcanic eruption
A landslide above sea level which causes materials to plunge into the water
Tsunamis can travel long distances and cause widespread destruction at coastal areas
In 2004, a 9.2 magnitude earthquake occured in the Indian Ocean and triggered a tsunami with waves that caused damage to coastal communities in 12 countries. The most damage was experience in the low-lying coastal areas of western Sumatra, including the city of Banda Aceh. The tsunami waves were between 4 to 39 metres high, and went as far inland as 10 kilometres
Landslides
Landslides are rapid downslope movements of soil, rock and vegetation debris from a slope. They can range from several metres to several kilometres in both length and width
In 1970, an earthquake off the coast of Peru destabilised the slopes of Mount Huascaran and triggered a massive landslide. The landslide travelled at more than 160km/hr and completely flattened the city of Ranrahirba within seconds. The death toll is more than 18000 and only 200 people survived the disaster.
Disruption of services
An earthquake can disrupt services such as the supply of electricity, gas and water and can potentially affect a large area. Vibrations on the ground can snap pipes and break cables which may cause the outbreak of fires. Communication services such as telephone connections may also be affected.
The earthquake in Kobe, Japan in 1995 damaged pipes and transmission lines. This disrupted electricity, gas and water supplies to around a million of Kobe city’s 1.4 million residents
Destruction of properties
Earthquakes can cause widespread destruction to many homes. People may be without homes after the disaster and reside a temporary shelter while their homes are being rebuilt
The earthquake in Tohoku, Japan in 2011 caused a tsunami which travelled up to 10 kilometres inland. Extensive structural damage resulted in hundreds of thousands of people being forced to leave their homes
Destruction of infrastructure
Earthquake may cause cracks to form in infrastructure such as roads and bridges. Transportation can be disrupted as it is unsafe to use the damaged roads
For example, after the earthquake in kobe, japan, in 1995, many places in the city became inaccessible or difficult to reach. Japan’s total cost of repair after the earthquake in tohoku, in 2011 was US$300 billion
Loss of lives
Earthquakes and their associated hazards often threaten the lives of those living in earthquake zones
The earthquake in Haiti in 2010 resulted in an estimated death toll of 300000 people
Massive destruction by volcanic materials
Volcanic materials can lead to widespread damage of property. Lava has high temperatures and burns the areas it flows through. Low-silica lava moves rapidly and flows over long distances, causing damage to larger areas. A pyroclastic flow can destroy everything in its path with hot rock fragments with speeds greater than 200m/s. Inhaling hot ash and gases can result in serious injury or death. Volcanic bombs can fall in areas surrounding the volcano and cause damage to property. Landslides have the potential to obstruct the flow of rivers causing floods, blocked roads, and buried villages and farmlands
The eruption of Nevado del Ruiz in the Andes Mountains of South America in 1985 released a pyroclastic flow. The mixing of pyroclasts and glacier ice along its path triggered lahars. The lahar engulfed the town of Armero and killed more than 20000 people
Pollution
Ash particles ejected during a volcanic eruption can disrupt human activities over large distances from the volcano. Thick plumes of ash may eventually settle on the ground and block sunlight, suffocate crops, and cause severe respiratory problems for people and animals
The eruption of Eyjafjallajokull in Iceland in 2010 produced extensive volcanic ash clouds containing tiny particles of abrasive glass, sand and rock. These particles posed a serious danger to aircraft engines and resulted in the closure of air space over much of Europe. The cancelled flights caused delays to 1.2 million passengers daily and cost the airline industry a total of US$1.8 billion
Fertile soil
Lava and ash from volcanic eruptions break down to form fertile volcanic soils which are very favourable to agriculture
The volcanic soils of Java and Bali in Indonesia support the cultivation of crops such as tea. This is the main reason why these two islands have been able to support a large rural population over many decades. Despite continuous use, the soils are more fertile than most non-volcanic areas of Indonesia
Precious stones and minerals
Volcanic rocks can be rich in precious stones and minerals. Precious stones like diamonds are formed when heated and pressurised carbon is cooled in magma pipes beneath the earth’s surface
The old volcanic rocks at Kimberly in South Africa are one of the world’s richest sources of diamond
Tourism
Volcanic areas offer a variety of activities for tourists to engage in. It is also rich in histsory and people can visit these areas to learn more about them
The ruins of Pompeii, Italy, were buried by layers of ash from the nearby Mount Vesuvius when it erupted in 79 CE. The unearthed archaeological site has revealed buildings left intact. Almost 3 milion people visit the site every year.
Geothermal energy
When groundwater comes into contact with hot rocks beneath the surface, it heats up and erupts as hot water or steam which can be harnessed to drive turbines and produce elecricity
Most of Iceland’s electricity is generated from geothermal power because of the large number of volcanoes in the country. Over 70% of homes in iceland are heated by volcanic steam
Account for the difference in the shape of the volcanic soils
For shield volcano, the silica content of the lava is lower so it is less resistant to flow. The lava travels further away from the vent before solidifying to create a cone with a broad base but gentle slopes.
For stratovolcano, the silica content of the lava is higher so it is more resistant to flow. The lava cannot travel far but solidfy close to the vent, creating a cone with a narrow base but steep slopes
