HAZARDOUS ENVIRONMENTS -HAZARDS CAUSED BY TECTONIC PROCESSES

• ·         They occur on all types of plate boundary, At hot spots away from plate boundaries, At fault lines
• ·         When two plates try to move but become stuck against each other, stress builds up.
• ·         Eventually, the plates break free along a fault causing a sudden release of pressure and releasing a tremendous amount of energy, which sends seismic waves out from the focus
• ·         The focus is the point on the Earth’s surface immediately above the focus is the epicentre.
• ·         Seismic waves are strongest at the epicentre

v  DESTRUCTIVE/CONVERGENT plate boundaries have shallow, intermediate and deep earthquakes inclined along the Benioff Zone on the subducting plate where slap pull occurs

v  COLLISION plate margins of two converging continental plates, such as between the EURASIAN & INDIAN plates where the Himalayas formed

v  CONSERVATIVE plate margins where faults, such as SAN ANDREAS IN CALIFORNIA, have earthquakes but no volcanic activity. In this case the NORTH AMERICAN & PCAIFIC plates are moving side-by side.

• Great friction builds up between the plates as they catch against each other and is eventually released in very powerful earthquakes usually from a shallow focus

v  CONSTRUCTIVE plate margins at mid-ocean ridges where ridge push occurs. The lithosphere is too weak and thin for a lot of stress to build up, so large earthquakes do not occur

• A volcano results from the build-up of molten material emitted onto the surface through an opening or fissure in the crust
• An active volcano has erupted in the last 80 years
• Dormant volcanoes are inactive but may become active again in the future
• Extinct volcanoes will not erupt again

v  SHAKING

• Earthquakes send out seismic energy waves, which are recorded by seismographs
•   PRIMARY (P) WAVES travel fastest and arrive at a place first, followed by SECONDARY (S) WAVES
•   The slowest waves are SURFACE WAVES, they travel along the Earth’s surface. Being long waves with large amplitude they cause the most of the damage as they shake the ground most violently

v  MEASURING EARTHQUAKES

Ø  The total amount of energy released/ magnitude of an earthquake is measured on the RICHTER SCALE

Ø  The number of earthquakes increased as their magnitude decreases

Ø  The 12-point MERCALLI SCALE measures the intensity of an earthquake

Ø  The focus of an earthquake can be up to 700km deep. Below that rocks are so hot they bend rather than break

Ø  Deep focus earthquakes are generally not as destructive as shallow focus ones, because of the thickness of rocks above the focus that absorb the shockwaves

v  TSUNAMIS

Ø  These are high, long-period waves in the ocean, resulting from a sudden displacement of the sea bed along a fault

Ø  In the open sea tsunami wave crests are small and wave lengths very long, making them difficult to monitor. When the wave crests reach shallow water at the coast, they slow and this dramatically in height.

Ø  The waves then retreat, pulling water back out to sea, before returning to hit the coast with tremendous force.Their heights can exceed 30m and they can flood thousands of kilometres away from the focus

Ø  Coastal areas near earthquake epicentres have little or no warning because a tsunami travels very rapidly. The tsunami generated by the large earthquake off the West coast of Sumatra on 26th December 2004 reached Aceh province a few minutes afterwards, so people fleeing from the earthquake were caught in the flood that surged inland.

v  SOIL LIQUIFACTION

Ø  This occurs when the shaking of the ground makes weak or unconsolidated rocks act as liquids and flow, leading to the sinking and destruction of buildings.

Ø  This occurs when groundwater is near the surface and soft sediment like sand mixes with water

LANDSLIDES

Ø  In April 2015, a shallow 7.9 magnitude earthquake struck Nepal with its epicentre 80km north-west of KATHMANDU.

Ø  Climbers at the south base camp on Mount. Everest, about 200 km away, reported that after the ground shook there was a massive fall of rocks, snow and ice down the mountain, causing 19 deaths in the camp. Landslides blocked roads, delaying the arrival of aid

1. Gases
• Water vapour constitutes up to 80% of the gases emitted and after conversion conversion to rain is responsible for dangerous mudflows and lahars

• Other gases include carbon dioxide an average of 200 million tons a year, sulphur dioxide which can corrode aircraft and hydrogen sulphide which is toxic

• A long period of inactivity and highly viscous magma causes such a solid plug to grow in the vent of a volcano that highly gas charged lava eventually explodes sideways out of a weakness in the flank of the volcano in a primary hazard known as nuée ardente

• A very hot incandescent cloud composed of gas and tiny fragments of solid material moves very rapidly down the slope keeping contact with it if temperatures can reach 1000 degrees celsius

• Only two people out of 30000 survived when a new adonte road down the capital town of st. Pierre from Mt. Pelée on Martinique in the Caribbean in 1902

LIQUIDS

• Lava is both the liquid material that flows out of the carter of the volcano and the rock it forms when solidified. It's originates from magma, molten rock beneath the surface , which rises from a magma chamber beneath the volcano through a vent to reach the surface

• The most dangerous lava flows are runny basalts, which occur at constructive plate boundaries and oceanic hotspots. As they move at 50 km an hour anything in their path is rapidly covered

• The fastest basalt lovers are of the aa-type formed when a lot of lava erupts quickly. Aa lava is thick, up to 10 metres deep with the surface that breaks into rough clinkers as it moves. Its steep slope in front moves forward as a unit with sudden dangerous surges of speed destroying anything it touches

• Slow flowing pahoehoe larva is less than 2 meters thick because it forms when low volumes are ejected more slowly. As it solidifies while moving, its smooth surface has curved flow lines, giving it a rope like appearance. Is flaws in individual lobes, moving around obstacles, setting flammable objects on fire as it does so. It is less viscous than in aa lava it cools more slowly and flows further

• PYROCLASTIC MATERIAL is solid particles that reach the ground in pyroclastic falls (airbone reach the ground in pyroclastic falls (airbone PYROCLASTIC MATERIAL is also known as tephra) . Some of it is the shattered remains of the plug that solidified in the vent after the previous eruption. Other pieces form when molten lava solidified while in the air.

• Solid materials are categorised by their size and shape: ASHES, the smallest, are less than 4mm in diameter while CINDERS are about 4 to 5 mm in diameter and LAPILLI are pebble sized. Volcanic block a large angular fragments resulting from the shattering of solid lava during an eruption, where is volcanic bombs are rounded because they form as molten lava cool while speeding through the air. All injections of pyroclastic material can be dangerous as it is usually hot it is also heavily and even ash can collapse roofs and cause damage to crops, machinery and electronics and people's lungs.

• Heavier particles such as bombs usually fall to the ground within 3 kilometres of the vent but the lighter particles can rise high into the atmosphere where they can damage aircraft engines. The enormous ash cloud emitted by EYJAFKALLAJÖKULL in 2010 drifted over europe from iceland and disrupted flights for more than a week, more than 100000 for a cancelled costing airlines almost 2.5 billion us dollars

• When lava domes collapse, hot dry rock fragments and gases move rapidly away from the vent down slopes and valleys by gravity. These pyroclastic slopes and valleys by gravity. These pyroclastic flows kill almost half the people who die as a result of volcanic eruptions.

• Their highly destructive nature results from their high density, fast speed travel, long distances covered and intense heat. The density of material is lowest at the top of the cloud and greatest in its base flow. The densest parts containing boulder sized fragments moves in contact with the ground and destroys everything with which it makes contact.

• Above the base flow hot gases keep the ash fragments buoyant. The heat sets nearby buildings, forest and crops on fire and people and animals on the edge of the flows die from breathing in the hot gases. Wide areas are buried by hot pyroclastic debris up to 200 m thick that often welds together. If loose, it can provide material for equally hazardous lahars to occur if water is added to the deposit

STRATOVOLCANOES these form at this destructive plate boundaries where the magma gains added silica as it rises through continental rocks. As the lava is intermediate between acidic and basic it is more viscous resulting in steep sides which usually steepen towards the summit giving a concave slope overall. Stratovolcano are particularly dangerous because they have long dormant period so people are not always convinced that they should heed warnings to evacuate during dormancy a fake plug of solidified magma builds up in the vents and as the magma has a high viscosity a considerable amount of pressure has to build up to unblock the vent usually culminating in an explosion which shatters the plug into pyroclastic fragments followed by the outpouring of lava. ORSORNO IN CHILE

1. CINDER CONES cinder cones form when blobs of gas charged lava are thrown into the air and break into fragments. The inappropriately named Lava Butte in Oregon is an example during it's growth it blocked and diverted the Deschutes river

2.LAVA DOMES these relatively small domes, with steep sides and rounded tops can form on the slopes of, or in the creators of stratovolcano. They are composed of silica lava which is too viscous to flow far, so solidifies quickly, forming a thick crust. Domes swell as they grow from within. Very explosive eruptions results when they collapse

3. SHIELD VOLCANOES these a form of basic lava, containing less than 50% silica. Consequently its fluid, flows long distances and solidifies slowly. If it issues from fissures, is forms extensive plateaus like the Deccan in India, but shield volcanoes results when there is a central vent. These volcanoes are enormous with very wide basis and gentle slopes of about 5 degrees

• VULCANIAN - eruptions are more violent because the more viscous lava solidifies more quickly and traps gases. Ashes and cinders are emitted when pressure is released. Dark, ash-laden clouds rise to form

• VESUVIAN - the viscous magma gains a high gas content during long periods of inactivity and deep plug forms, which can only be blown off after considerable pressure has built up. The violent eruption sends a wide, dark ash cloud into the stratosphere. Ash falls over a wide area.

• PLINEAN - a very violent explosion of gas, ash and pumice results in a narrower cloud that extends into the stratosphere. The ash cloud from Mt. Pinatubo's 1991 eruption circulated the world several times in the stratosphere, causing temporary global cooling about 0.5°c temporary global cooling about 0.5°c

• PELÉAN - highly viscous magma and a long period of inactivity cause an explosion out of a weakness in the side of the volcano, with a nuée ardente

• ICELANDIC - fluid basalts issue quietly from fissures at mid-ocean ridges

• HAWAIIAN - fluid basalts issue from vents in volcanoes. Gases escape easily and quietly with occasional spurts of gases from lava lakes causing lava fountains

• STROMBOLIAN - less fluid lava and gases escape with moderate explosions in which lava bombs are ejected. Stromboli is known as ' The lighthouse of the Mediterranean' because of its very frequent activity.

• Lahars these volcanic mudflows form when water mixes with loose pyroclastic material, with particle sizes varying from small debris to boulders, forming flows resembling wet concrete down the slopes of volcanoes and into valleys beyond them.The source of water can be the intense rainfall accompanying the eruption, glacier melt, snow melts or dam failure.

• Lahars are dense and viscous by flow very fast, reaching speeds of 75 km an hour. The more volcanic material they contain the faster they flow and the more destructive they are.They are most common on steep slopes of stratovolcano where the downward pull of gravity is strong but can occur on shield volcanoes as in Iceland. They quickly increase in size as they gain more water and erode more material to carry but die out as they move away from the volcano

• Volcanic landslides these masses of rock and soil moving downslope under gravity can be dry or wet although they are drier than lahars. With addition of water as they flow they can transform into lahars if they contain more than 3% fine clay particles. The landslide originates as a large slab of rock disintegrate into progressively smaller particles as they move downslope. a volcanic landslide can be as huge as 100 kilometres cubed in volume and faster than 100 km/hr.
• Volcanic landslides result when magma forces its way to the surface and pushes outwards, causing the rock to break or over-steppen and collapse by gravity down the high, steep sides of the stratovolcano. They can also be triggered by large earthquakes beneath a volcano.
• Volcanic landslides trigger volcanic eruptions by removing the lid on the gases and rising magma. They bury valleys and after coming to rest cause lahars as water drains down the valley from them. 

• At DIVERGENT / CONSTRUCTIVE plate boundaries (Iceland) and OCEANIC HOT SPOTS ( Lanzarote, Galapagos Islands and Easter island), there are shield volcanoes. The magma/lava erupts on the ocean floor, so it is magic (e.g. basalt), basic and fluid. Other emissions are effusive as lava flows with fire fountains and ash flows. Routed followed depend on gravity, relief and the viscosity of the flow. Secondary activity include, floods and occasional big ash clouds that disrupt air traffic, like in Iceland 2010.
• At CONVERGET/ DESTRUCTIVE plate boundaries (especially along the Pacific Ring of Fire), there are stratovolcanoes and dome volcanoes. Magma/lava rises through silica-rich continents so it is mostly silicic (e.g. rhyolite, andesite), acidic and viscous. Other emissions are explosive such as pyroclastic flows, nuée ardentes and ash affect wide areas. Secondary activity include lahars, global cooling from atmospheric ash clouds and floods.

• Amount of energy released
• Depth of focus- The shallower the focus the greater the effect. The rocks above absorb some of the enrrgy of deep-focus earthquakes.
• Number and strength of foreshocks and aftershocks. Buildings weakened or damaged by 1 earthquake may collapse when further damaged by another.
• Distance away from the epicenter. As the distance increases, the strength of the shockwaves decreases.
• Nature of the bedrock. If it is solid damage is limited but where rocks are weak or loose sands or clays, liquefaction can occur. It can be very destructive particularly on a slope.
• Population density at or mnearvyhe epicentre
• Strength and type of the buildings. Modern buildings in earthquake zones and economically developed countries are usually strengthens against earthquake damage
• The time of day is also significant during the night they'll be fewer deaths in strongly built homes than at rush hour when people on the streets are likely to be hit by falling masonry. More people are out of their homes during weekdays than weekends.
• Deaths also depend on risk perception, which leads to the amount of preparation by the population and by emergency services before, during and after the events this is greater in HICs than LICs, where funding is a problem.

Earthquake primary impacts
• Deaths, injuries, panic and shock caused by collapsed buildings and bridges.
• Roads are destroyed as vertical movements cause fault scarps to develop or the ground is offset horizontally.

Earthquake secondary impacts
• Soil liquefaction, caused by shaking, leading to buildings sinking.
• Homelessness, lack of shelter and loss of livelihoods occur.
• People living in temporary tented accommodation or sleeping outside in areas with cold winters or very cold nights can die from hypothermia.
• Water often becomes contaminated with sewage, leading to disease.
• Fires and lack of power are caused by the destruction of electricity cables and gas pipes.
• Water shortages and thirst result from broken water mains.
• Breakdowns in telephone and internet connections, mudflows, landslides and tsunamis can occur.
• Famine can be a long-term effect
• Theft and other crimes can result.

Volcanic eruption primary impacts
• Lava flows, ash and tephra falls, pyroclastic flows, release of gases and nuée ardentes

Volcanic eruptions secondary impacts
• Lahars, landslides, tsunamis from undersea eruptions.
• Crop damage and famine, loss of homes and livelihoods
• Disruption to flights where ash clouds occur, long-term cooling of the atmosphere 

• The New Zealand Earthquake Commission predicts a major earthquake will happen in Christchurch everybl 55 years. It is not possible the predicts exactly when an earthquake will occur or where it's epicentre will be. Short term predictions cannot be made. Most majorvearthquakes occur along plate boundaries as a result of a cycle in which strain builds up and is eventually released. The average movement of plates, usually a few millimeters a year, has been calculated but it is not know exactly where in the cycle a particular location is

• Geologists use the SEISMIC GAP THEORY to work out where a strong earthquake is likely to occur. 'Gap' refers to the section of an active fault that has not experienced earthquakes for a considerable time compared with other segments along that fault. All parts of the fault are expected to experience the same degree of displacement over time.

• The location of the 1989 earthquake in the San Francisco Bay area along the San Andreas fault was at a known gap. Using past records, the frequency of earthquakes along part of a fault is calculated to predict the next one and the rate of movement of sections along the fault is also used. The longer the period without an earthquake, the greater the accumulated stress and the greater the likelihood of a strong earthquake

 - horizontal movements are detected by measuring the change in the time it takes a laser beam to move between two fixed points on either side of a fault.

- changes in slope are detected by a tilt meter, which is like a very sophisticated spirit level.

- variations in the Earth's magnetic field, resulting from changes in stress in the rocks, are measured by a magnetometer.

- seismograph records are monitored. Clusters of small earthquakes often precede a large one.

- the amount of radon gas rising to the surface is measured, as it can increase before an earthquake. 

• This is undertaken to show areas of ground that are likely to liquefy, fault locations and dared of past movement, past earthquakes epicentre with magnitudes and dates and areas where landslides and tsunamis might result.

• After the 2008 earthquake in Sichuan, which destroyed a school built on a fault, geologists started searching for fault locations to map them as unsuitable locations for development. Ground movements leave earthquake scarps, which need to be mapped, but this vital evidence is often quickly removed by erosion and landslides. However, the authorities in Sichuan could not wait for the maps to be completed before they rebuilt and the replacement buildings are not strong enough to survive an earthquake of the same magnitude. There are now many vulnerable large cities in earthquake belts in China.

4. Hard engineering : engineer geologists know what infrastructures need replacing, moving or strengthening. It is cost-effective to make the necessary changes rather than meet the expense of restoration after a strong earthquake.

5. Strengthening buildings : there is little space for building in mountainous Japan, so skyscrapers are built in a pyramid shape for strength. In Japan, buildings have a damper in the roof which acts like pendulum, reducing building swaying. Also there is cross bracing which stops floors from collapsing. There are shock absorbers built into cross braces, a strong steel frame which is also fexiblr to stop cracking. There is strong double glazed windows to stop broken glass showering down. Very deep foundations to prevent collapse. Piles made out of alternate layers of steel and rubber to make it flexible.

6. Land-use zoning : land uses, such as oil storage depots, that are potential fire or explosion risks are positioned away from homes, and are built on solid rock. Land likely to liquefy is used for playing fields, nature reserves and parks, not buildings

7. Increasing risk perception : earthquake drills allow people to practice what to do in an earthquake and our regular events in schools and workplaces in many tectonic areas. Japan holds an earthquake awareness day each year so everyone will be able to follow emergency procedures without panic. Evacuation points with water food and medical supplies are placed in every neighborhood. People are giving maps of routes to follow and leaflets about how to dress and what to take. They informed how to improve safety in the home such as securing furniture to the walls and knowing how to switch off the gas supply. In Japan gas supplies automatically switch off in an earthquake to reduce the fire risk. People are advised to keep a survival pack near an exit and to have food and drink available to last at least 3 days.

• When I said make a vent is detected that could cause a tsunami and tsunami watch is started. Sea level height detectors confirm if one has been generated. An international Tsunami Early Warning System operated by NOAA in hawaii covers the pacific ocean. Seismograph stations and tidal stations spread across the ocean send automatic warnings to hawaii as soon as the water reaches a certain height. Satellite monitor the tsunami as it crosses the ocean. Communication systems at threatened coasts, warned by the center in hawaii make residents aware of the impending danger by various methods including text messages and evacuation procedures are put into place. After the 2004 tsunami and international warning system was set up for the indian ocean.

Remote sensing by satellite sensors the text deformation of the ground surface and temperature changes caused by heating in the ground before an eruption. Gravity metres on the ground the traditional changes due to magma movement. Geochemical changes are also indicative of an impending eruption. Thermal waters such as hot springs on volcanoes have increased levels of CO2 and H2and He dissolved in them before an eruption. Chemical sensors also measure increased sulphur levels. 

In Iceland and Hawaii cold water was hosed on lava flows to cool them and reduce their flow lengths. On Etna lava flows were bombed and diverted away from settlements by channels and in 1992, when the town of Zafferana was threatened, large concrete blocks were dropped into lava tubes from which the lava was flowing, it stopped before it reached the town.

People live near tectonic hazards because:
• The hazard may not have been predicted

• People may be unaware of the danger is the volcano is dormant or there has been no large earthquake in recent time

• they are reluctant to leave their place of birth family or friends 

• Some, such as the afghan people take a fatalistic attitude that has it cannot be controlled so it has to be accepted

• the perception of the risk is that it will happen to others but not to them so they do not accept that they need to take action to reduce risk people interviewed after hazard often comments that it is something that happens elsewhere but was not expected to happen to them

• Economic reasons, some people are reluctant to leave your jobs. Sulfur is mined from active volcanoes and basic lavas weather to fertile soils suitable for intensive agriculture as on the densely populated island of Java. Geothermal energy in volcanic areas leads to industrial development and cheap heating for homes and for crops grown in hothouses as in Iceland. The dramatic volcanic landscape attracts tourism which encourages population growth. For such reasons people believe that the benefits from living and hazardous areas will be greater than the cost of doing so.