tectonics/natural hazards

“A natural event (for example earthquake, volcanic eruption, tropical storm, flood) that threatens people or has the potential to cause damage, destruction and death.”

There are different types of natural hazards that can affect people around the globe, including;
• Atmospheric hazards - Created in the atmosphere, by the movement of air and water
• Terrestrial/Geological hazards  - Created by the movement of the Earth's tectonic plates  or surface rock and soils
• Water based hazards - Created by rivers, sea or oceans
• Biological Hazards - Any biological substance that poses a threat to the health of people

NATURAL FACTORS - a gently sloping coastline will often suffer more damage than a steep coastline in a hurricane’s storm surge. It is known that generally earthquake shaking in soft sediments is larger and longer than when compared with the shaking experienced at a "hard rock" site. Softer sediments are more likely to liquefy too, which can contribute to building collapse.

MAGNITUDE - A hurricane of magnitude 5 on the Saffir Simpson scale will have more impact than that which has a magnitude 3, whilst every step up the Earthquake Richter scale represents a 10 fold increase in damage and a 30 fold increase in energy released.

POPULATION DENSITY - greater the number of people in an area, the greater the potential for disaster.

EDUCATION – regardless of level of development people can be educated to survive natural hazards.  Education about the risks of contaminated flood water or Earthquake drills (like the ones Japan has on the 1st September to commemorate the 1923 Tokyo Earthquake) can save many lives.

MANAGEMENT-
Predict – some natural hazards are easier to predict than others, hurricanes can be identified by satellites and then tracked.  This allows governments to evacuate if needed.
Preparations - if a place is well prepared regardless of its level of development this can limit the impact of a hazardous event.  In India, despite its low level of economic development, rounded wooden houses have been designed to be earthquake proof, thus limiting the impact of these hazards.
Prevent – this could be preventing damage to buildings etc. through strict building rules.

 TECH– HICs can afford the technology to help them predict events, the USA has the United States Geological Survey to collect earthquake data from seismometers for example.  They also have the technology to help buildings survive various natural hazards

• Plate boundary - the boundary or margin between two tectonic plates.
• Tectonic hazard - a natural hazard caused by movement of tectonic plates (including volcanoes and earthquakes).
• Tectonic plate - a rigid segment of the Earth’s crust which can ‘float’ across the heavier, semi-molten rock below. Continental plates are less dense, but thicker than oceanic plates.

Plate Tectonics is a theory that tries to explain how the Earth is structured and what it is made up of. Tectonic plates are moving about very slowly, pushed and shoved around from underneath by currents within the mantle called convection currents. Another theory suggests that this is more localised, with slabs of crust pushed apart at constructive plate margins (SLAB PUSH) and where the plates increase in density away from these margins get pulled down into the mantle (SLAB PULL) by gravity and local convection cells.

Continental crust is thicker, older and lighter, and is composed mainly of Granite. It is 22 mi (35 km) thick on average and less dense than oceanic crust. Continental crust is more complex than oceanic crust in its structure and origin and is formed primarily at subduction zones at destructive plate margins.
Oceanic crust is younger and heavier, and is mainly composed of basalt and Gabbro. It is mainly formed at constructive margins or spreading mid ocean ridges.

The major plates include the Pacific, Eurasian, African, Antarctic, North American and South American, and the Indo-Australian. There are other smaller plates however, such as the Philippines and Cocos plates. The tectonic plates join at zones called plate margins, where most of the world’s volcanic and earthquake activity occurs. Remember that this is a theory proposed by Alfred Wegener as CONTINENTAL DRIFT in 1912, and is now supported by lots of evidence since.

• Conservative plate boundary - Tectonic plate margin where two tectonic plates slide past each other.
• Constructive plate boundary -Tectonic plate margin where rising magma adds new material to plates that are diverging or moving apart.
• Destructive plate boundary - Tectonic plate margin where two plates are converging or coming together and oceanic plate is subducted. It can be associated with violent earthquakes and explosive volcanoes.

At this type of plate margin two plates are moving apart (DIVERGE) from each other in opposite directions. Convection currents moving in opposite directions (caused by the intense heat of the Earth's interior) in the mantle move two plates apart. As these plates move apart this leaves cracks and fissures (lines of weakness), that allows magma from the mantle to escape from the highly pressurised interior of the planet. This magma fills the gap and eventually erupts onto the surface and cools as new land. This can create huge ridges of undersea mountains and volcanoes, and where these mountains poke above the level of the sea, islands are created. Both earthquakes and volcanoes can result at these margins, the earthquakes caused by the movement of magma through the crust. A really good example of this is the Mid-Atlantic Ridge, where the Eurasian plate moves away from the North American plate at a rate of around 4cm per year. Iceland owes its existence to this ridge.

At conservative margins mountains are not made, volcanic eruptions do not happen and crust is not destroyed. Instead, 2 plates either slide past each other in opposite directions, or 2 plates slide past each other at different speeds. As they move past each other stress energy builds as the plates snag and grind on one another. When this stress energy is eventually released it sends shock waves through the earth’s crust. We know these shock waves as earthquakes, and a good example of this is the San Andreas Fault in California, where the Pacific plate is moving NW at a faster rate than the North American plate.

At these margins 2 plates move or CONVERGE together and the destruction of some of the Earth's crust results. An oceanic plate (denser) is pushed towards a continental plate (less dense) by convection currents deep within the Earth's interior. The oceanic plate is subducted (pushed under) the continental plate at what is called a subduction zone, creating a deep ocean trench. It is the Oceanic crust which sinks down into the mantle because it is denser (heavier). As it descends friction, increasing pressure and heat from the mantle melt the plate. Some of this molten material can work its way up through the continental crust through fissures and cracks in the crust to collect in magma chambers. This is often some distance from the margin where magma can eventually re-emerge at the surface to create a range of mountains. The movement of the plates grinding past one another can create earthquakes, when one plate eventually slips past the other releasing seismic energy. There are several really good examples of destructive plate margins, including along the West coast of the Americas and Japan, where the Philippines sea plate is pushed under the Eurasian plate.

At least 15,550 people killed, 5,344 missing, 5,314 injured, 130,927 displaced and at least 332,395 buildings destroyed this led to many blocked roads and massive problems of homelessness.

the total economic loss in Japan was estimated at 309 billion US dollars.

Electricity, gas and water supplies, telecommunications and railway service disrupted

east coast of Honshu, Japan, occurred as a result of thrust faulting on or near the subduction zone interface plate boundary between the Pacific and North America plates. 

magnitude-9.0 earthquake 

New laws were passed to make buildings and transport structures even more earthquake proof.

Operation USA began immediately working to address needs for material aid in the face of the enormous damage caused by the earthquake and tsunami, with a focus on shelter and medical supplies.

japanese red cross mobilised 230 emergency service teams fir medical and emotional support

shelters set up un schools

Port Au Prince, the capital, is on a fault line running off the Puerto Rico Trench, where the North American Plate is sliding under the Caribbean plate. 7.0 on the Richter Magnitude scale.

•316,000 people died and more than a million people were made homeless, even in 2011 people remained in make shift temporary homes.  Large parts of this impoverished nation were damaged, most importantly the capital Port Au Prince, where shanty towns and even the presidential palace crumbled to dust. 3 million people in total were affected. Few of the Buildings in Haiti were built with earthquakes in mind, contributing to their collapse

•Rubble from collapsed buildings blocked roads and rail links.
• The port was destroyed
• Sea levels in local areas changed, with some parts of the land sinking below the sea
• The roads were littered with cracks and fault lines

Communication systems, air, land, and sea transport facilities, hospitals, and electrical networks had been damaged by the earthquake, which slowed rescue and aid efforts.

The EU gave $330 million and the World Bank waived the countries debt repayments for 5 years.

USA took charge of trying to coordinate Aid distribution

Between 23 major charities, $1.1 billion had been collected for Haiti for relief efforts, but only two percent of the money had been released
• One year after the earthquake 1 million people remained displaced
• The Dominican Republic which neighbours Haiti offered support and accepted some refugees.

olcanic soils are fertile  as the weathering of volcanic rock releases potassium into the soil, which is essential for plant growth e.g. Naples, Italy has olives, vines, nuts and fruit (mainly oranges and lemons) growing area to Mount Vesuvius.

Tourism is a popular activity in these areas. Mount Etna, attracts thousands of tourists, who travel in cable cars and 4 wheel drives to the crater, providing a range of jobs for local people. The Blue Lagoon in Iceland is heated by geothermal heat and  1.2 million people visited the Lagoon in 2010

n Iceland volcanoes provide cheap geothermal power, 28 % of all its energy. This is even used to heat pavements in winter in Reykjavik.

Poor people, especially in LICs cannot afford to live away from volcanoes as they provide jobs and their families and friends live there.

Management strategies - Techniques of controlling, responding to, or dealing with an event.
• Monitoring - Recording physical changes, such as earthquake tremors around a volcano or tracking a tropical storm by satellite, to help forecast when and where a natural hazard might strike.
• Planning - Actions taken to enable communities to respond to, and recover from, natural disasters, through measures such as emergency evacuation plans, information management, communications and warning systems.
• Prediction - Attempts to forecast when and where a natural hazard will strike, based on current knowledge. This can be done, to some extent for volcanic eruptions and tropical storms, but less reliably for earthquakes.
• Protection - Actions taken before a hazard strikes to reduce its impact, such as educating people or improving building design.

Earthquake proof building

Planning
We can also plan for earthquake and volcanic activity.  Prior to events we can plan where we will or will not allow building.  Preventing building on softer sediments can protect people from the worst of the shaking and liquefaction during earthquakes for example.  Plans should also be in place prior to events so that emergency services know what to do during a volcanic or earthquake event

Seismometers
For earthquakes the equipment above is used plus other equipment and measures, these include;
Using foreshocks by monitoring seismic waves– we often get small earthquakes before “the big one” that can give warnings. The Japan Tsunami (mag 9.0) was preceded by a massive magnitude 7.2 earthquake.

Seismic waves
Scientists can use seismic or earthquake waves to show if a volcano is getting ready to erupt. Many volcanoes experience an increasing intensity in frequency and size of earthquakes as they prepare to erupt. We can monitor these using seismometers which produce seismographs.  This technique was used in Nevado Del Ruiz in 1985 and for Mount Pinatubo in 1991.