Plate tectonics and associated hazards 1

On 11 March 2011, a 9.0 magnitude earthquake off the north-eastern coast of Japan – the strongest ever recorded in the country – triggered a tsunami up to 30 metres high that washed up to 5 kilometres inland. It resulted in massive loss of life, environmental devastation and infrastructural damage. The disaster also damaged several nuclear power plants, leading to serious risks of contamination from radioactive releases.

Choose which environmental issues require attention during the recovery phase:

Soil and groundwater: When seawater penetrates far inland, land salinity (and hence agricultural productivity) and shallow groundwater quality (if used for drinking or irrigation) can be affected;

  • De-silting of coastal canals: Coastal waterways were fully silted by the tsunami and will need to be drained in order to become operational;
  • Water supply and sewage networks: Damage to urban water supply and sewage networks can result in cross contamination, leading to health impacts for the population;
  • Coastal ecosystems: Coastal habitats and ecosystems can be destroyed, with implications for livelihoods; and
  • Environmental risks of reconstruction: Reconstruction operations can have a significant environmental footprint, particularly if environmental considerations are not taken into account in planning and managing operations such as waste disposal and clean-up.

Plate tectonics and associated hazards 2

Name the type of the tectonic plate boundary shown on the Figure below

There are two plates moving towards each other, and one is forced below the other into the mantle. Continental crust meets continental crust (note that this is very rare). These boundaries mark the site at which the Earth’s crust is at its thickest.

Plate tectonics and associated hazards 3

What is the climate impact on the Himalayas?

The Himalayas have a profound effect on the climate of the Indian subcontinent and the Tibetan plateau. It prevents frigid, dry Arctic winds from blowing south into the subcontinent, which keeps South Asia much warmer than corresponding temperate regions in the other continents. It also forms a barrier for the monsoon winds, keeping them from traveling northwards, and causing heavy rainfall in the Terai region. The Himalayas are also believed to play an important part in the formation of Central Asian deserts such as the Taklamakan and Gobi deserts.

The mountain ranges also prevent western winter disturbances from Iran from traveling further, resulting in snow in Kashmir and rainfall for parts of Punjab and northern India. Despite being a barrier to the cold northerly winter winds, the Brahmaputra valley receives part of the frigid winds, thus lowering the temperature in the northeast Indian states and Bangladesh. These winds also cause the North East monsoon during this season for these parts.

In turn, the weather phenomenon called Jet Stream affects our image of the highest peaks on earth. The strong stream of winds from the west passes through Everest, creating a familiar plume of snows blowing from the summit, and visible from a great distance.

The Himalayas with dazzling pinnacles of snow-covered ranges extend for 2,250-km from the Namcha Barwa on the bend of the Tsang-po (Brahmaputra) to Nanga Parbat on the Indus. The range runs east to west up to central-Nepal and then takes a southeast to northwest direction. The average width of the Himalayas is about 200-km.

Compositions of the forests on this mighty ranges are affected by the combined effect of altitude, rainfall and latitude. The rainfall, mainly from the monsoons, decreases from the east to the west. Comparatively, in winter, due to the influence of tropical west wind drift, the northwest areas have more precipitation in the form of rain and snow. From these snow covered ranges with big glaciers, flow the great rivers that have made the Indo-Gangetic plain one of the most fertile in the world and the heart Land of India.

Plate tectonics and associated hazards 4

Which main geophysical disaster is caused by tectonic plates in the Himalayas?

Himalayas, as a region, has always been susceptible to disaster, due to the neo-tectonic mountain-building process, like earthquakes, landslides, floods, etc.

It should be noted that the damages in the event of an earthquake primarily result from the unplanned developmental activities in seismicity-prone areas, which increase the casualties of life and loss of property manifold. Therefore special attention should be paid in undertaking major developmental activities like human settlements, urbanization, road building, laying of railway tracks etc. Japan, seismically one of the most vulnerable countries, has successfully shown that the damages accruing from an earthquake, even with a higher magnitude of 7 on the Richter Scale, can be minimized by adopting an integrated approach of generating awareness, building earthquake resistant structures, always keeping the level of preparedness at a higher level, and preparing and regular updating of elaborate disaster management plan in case of an eventuality.
 
Plate tectonics and associated hazards 5

Name the type of a tectonic plate boundary shown on the Figure

Destructive margins - plates move towards each other and one forces to be below the other into the mantle.

Plate tectonics and associated hazards 7

Read the definition and write down missed term.

_______________  the study of the fossil magnetism in rocks, used to determine the past configurations of the continents and to investigate the past shape and magnitude of the earth's magnetic field

Palaeomagnetism - the study of the fossil magnetism in rocks, used to determine the past configurations of the continents and to investigate the past shape and magnitude of the earth's magnetic field

Plate tectonics and associated hazards 8

Write down which type of plate boundary is Mid-Atlantic Ridge.

Almost all the Earth's new crust forms at divergent boundaries, but most are not known because they lie deep under the oceans. These are zones where two plates move away from each other, allowing magma from the mantle to rise up and make a new crust. Divergent boundaries are where the plates move apart. Seafloor spreading is a procces in which the magma creates new land under water and this process takes over millions of years to form a ten foot hill cause the growth ranges from two-ten centimeters per year. The magma is buoyant and creates more ridges and an example of this is Mid-Atlantic Ridge.  

Plate tectonics and associated hazards 9

Choose locations with convergent plate boundaries

Convergent plate boundaries:

  • Cascade Mountain Range
  •  St. Lucia and St. Vincent and the Grenadines
  • the Andes mountain range

Divergent plate boundaries:

  • Mid-Atlantic Range
  • West Antarctic Rift
  • Baikal Rift Zone
Plate tectonics and associated hazards 10

Choose examples of divergent (constructive) plate boundary

Divergent (constructive) plate boundary:

  •  the Mid-Atlantic Ridge exposed above sea level on the island of Iceland
  • the Mid-Atlantic Ridge between North America and Africa
  • the East Africa Rift

Convergent plate boundary:

  •  the Mid-Atlantic Ridge
  • Mariana Trench
  •  the Cascade volcanoes along the Washington-Oregon coast of North America
Plate tectonics and associated hazards 11

Watch on the picture below. Which process is shown schematically by it?

Seafloor spreading - is a process in which new ocean floor is created as molten material from the earth's mantle rises in margins between plates or ridges and spreads out.

Plate tectonics and associated hazards 12

Slab pull forces occur at which type of plate boundary?

Slab pull is the pulling force exerted by a cold, dense oceanic plate plunging into the mantle due to its own weight. The theory is that because the oceanic plate is denser than the hotter mantle beneath it, this contrast in density causes the plate to sink into the mantle. The process of a tectonic plate descending into the mantle is termed subduction.

Subduction zones are just one type of convergent boundary where two tectonic plates are colliding. Convergent boundaries can occur between two oceanic plates, such as in the south Pacific, and between an oceanic and a continental plate, such as on the northwest coast of the United States.

Plate tectonics and associated hazards 13

Read the definition below.

A dipping planar (flat) zone of earthquakes that is produced by the interaction of a downgoing oceanic crustal plate with a continental plate. These earthquakes can be produced by slip along the subduction thrust fault or by slip on faults within the downgoing plate as a result of bending and extension as the plate is pulled into the mantle.

Write down the term described by it.

Benioff Zone  -  a long narrow region, usually adjacent to a continent, along which earthquake foci lie on a plane which dips downwards at about 45° and along which the oceanic lithosphere is thought to be descending into the earth's interior. Compare subduction zone (named after Hugo Benioff (1899–1968), American seismologist, who first discovered the phenomenon)

Plate tectonics and associated hazards 14

Select only secondary hazards that may result from an earthquake.

Earthquakes occur because of a slow build up of pressure in the earth's rocks, which is quickly released.

Primary Hazards are hazards due directly to the earthquake itself, and consist of ground movement and shaking.

Earthquakes emit body waves (travel through the earth) and surface waves. It is surface waves that cause most damage as they impact on what is on the surface of the earth

Secondary Hazards are indirect hazards that may result from an earthquake:

Soil Liquefaction - Solid material changed into a liquid state. Damages building foundations, resulting in them sinking.

Landslides - Often as a result of the ground shaking, even if a slope is gentle. Cause burial of people and overrun buildings.

Tsunami (tidal waves) - If the focus of the quake is beneath the sea, tsunami can occur. Ninety percent occur in the Pacific basin. The more movement of the sea floor and the shallower the focus the larger the wave that is created.

Plate tectonics and associated hazards 15

Read careful the describtion and write down which shape of volcano is it.

Very gentle slope, found at diverging ocean plates, basaltic lava, can flow over large distances.

The shapes of volcanoes that you should be able to recall are:

  1. Fissure: Very gentle slope, found at diverging ocean plates, basaltic lava, can flow over large distances.

  2. Basic / Shield: Have gentle slopes, steeper than fissure due to repeated explosions and subsequent build up of basalt based lava. (Mauna Loa Hawaii)

  3. Cone: Symmetrical in shape, A acid where thick viscous lava, rapidly cools B) Ash / Cinder.

  4. Composite: Very large old volcanoes. Both ash and lava are deposited (Mt. St. Helens)

  5. Crater / Caldera: Form when a very violent eruption occurs after a build up of gas beneath the volcano. Can destroy the magma chamber leaving a large crater.

Plate tectonics and associated hazards 16

Read the describtion below and select which shape of volcano is it.

Form when a very violent eruption occurs after a build up of gas beneath the volcano.

The shapes of volcanoes that you should be able to recall are:

  1. Fissure: Very gentle slope, found at diverging ocean plates, basaltic lava, can flow over large distances.

  2. Basic / Shield: Have gentle slopes, steeper than fissure due to repeated explosions and subsequent build up of basalt based lava. (Mauna Loa Hawaii)

  3. Cone: Symmetrical in shape, A acid where thick viscous lava, rapidly cools B) Ash / Cinder.

  4. Composite: Very large old volcanoes. Both ash and lava are deposited (Mt. St. Helens)

  5. Crater / Caldera: Form when a very violent eruption occurs after a build up of gas beneath the volcano. Can destroy the magma chamber leaving a large crater.

Plate tectonics and associated hazards 17

Which shape of volcano is presented by Mauna Loa Hawaii

The shapes of volcanoes that you should be able to recall are:

  1. Fissure: Very gentle slope, found at diverging ocean plates, basaltic lava, can flow over large distances.

  2. Basic / Shield: Have gentle slopes, steeper than fissure due to repeated explosions and subsequent build up of basalt based lava. (Mauna Loa Hawaii)

  3. Cone: Symmetrical in shape, A acid where thick viscous lava, rapidly cools B) Ash / Cinder.

  4. Composite: Very large old volcanoes. Both ash and lava are deposited (Mt. St. Helens)

  5. Crater / Caldera: Form when a very violent eruption occurs after a build up of gas beneath the volcano. Can destroy the magma chamber leaving a large crater.

Plate tectonics and associated hazards 18

Read the describtion below and write down which type of lava flow is it.

Is fluid rather than viscous, but does not move quickly. Often the surface layer is static whilst flow continues beneath.

Types of lava Flow

This ranges from being extremely thick and viscous, to highly fluid. The amount of pyroclastic material also varies. The two types are:

Aa flow - This is a few metres thick, a mix of uneven shaped, sharp edged ash and cinder blocks. It is unstable.

Pahoehoe flow - Is fluid rather than viscous, but does not move quickly. Often the surface layer is static whilst flow continues beneath.