Earth Hazards

Tectonics

Definitions

Collision theory : plate boundary in which two similar plates come together – neither is destroyed but both are folded to form fold mountains, e.g. the Eurasian and Indian plates which collide and form the Himalayas.

Conservative boundary : plate boundary in which two similar plates pass each other –neither is destroyed but earthquake activity is common, e.g. the San Andreas fault where the North American plate and Pacific plate move in the same direction but at different speeds.

Constructive boundary : plate boundary at which new material is being created, e.g. Iceland. Also called a divergent boundary.

Destructive boundary : plate boundary at which material is destroyed at a subduction zone e.g. off the west coast of South America.

Epicentre : the point on the ground surface immediately above the focus

Focus : the point underground where the earthquake happens.

Primary hazards : the direct hazards associated with an event, for example ground shaking during an earthquake

Secondary hazards : the delayed hazards associated with an event, for example hypothermia that people may experience as a result of having to live outside after buildings have been destroyed.

Plate Boundaries

Where oceanic crust meets continental crust

Oceanic subducts under the continental

Deep trench created

E.g. Aleutian Trench

• Occur when two plates move past each other

• No formation or destruction of crust

• E.g. San Andreas fault

• Intense earthquake activity

New ocean floor material is created here

Forms mid-ocean ridges e.g. Mid-Atlantic Ridge

Fresh magma rises, cools and solidifies

As the ridge gives way, earthquakes and volcanoes occur

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Earthquake in a MEDC

Background Information

On 17th January 1995, an earthquake struck Kobe, a heavily populated urban area in Japan. It measured 7.4 on the Richter scale and occurred as a result of plate movement along the boundary between the Philippines Plate, Pacific Plate and Eurasian Plate.

Short term effects

35000 people injured.

Buildings and bridges collapsed despite their earthquake proof design.

Long term effects

Buildings destroyed by fire when the gas mains fractured.

316000 people left homeless and refugees moved into temporary housing.

Short term responses

People were evacuated and emergency rations provided.

Rescue teams searched for survivors for 10 days.

Long term responses

Many people moved away from the area permanently.

Jobs were created in the construction industry as part of a rebuilding programme.

Kobe, Japan, 1995

Earthquake in a LEDC

Background Information

On 8 October 2005, an earthquake measuring 7.6 on the Richter scale hit the Kashmir region of Pakistan. The earthquake was the result of collision between the Indian and Eurasian plates.

Short term effects Buildings collapsed. 79,000 people were killed. Landslides, and large cracks appeared in the ground.

Long term effects

Broken sewerage pipes contaminated water supplies and spread disease. People died of cold during the harsh winter.

Short term responses

The army and emergency services arrived to join the rescue effort.

Tents were given out by charities.

Aid workers arrived from abroad to find survivors and treat the injured.

Long term responses

Schools and hospitals were rebuilt.

Building regulations were improved to reduce damage and the death rate in future earthquakes.

Kashmir, Pakistan, 2005

Tsunamis

What causes a tsunami and what effects do they have?

A tsunami is a huge wave, usually caused by volcanic or earthquake activity under the ocean, which can eventually crash onto the shoreline. The effects on a community can be devastating.

What causes a tsunami?

When an earthquake, volcano or landslide happens on the ocean floor, water is displaced. This water forms the start of the tsunami.

When the waves reach shallower water:

their height can increase by several metres

the shallow water slows the wave

the waves get closer together

It is hard to see that a tsunami is approaching. The most obvious sign is the coastal water retreats just before the waves reach the shore. This is actually the trough of the wave following behind.

What effects does a tsunami have?

The main impact a tsunami has is flooding. The waters are also able to erode the foundations of coastal structures.

Tsunami Case Study

On 26 December 2004 a tsunami occurred in the Indian Ocean. It was the result of the Indio-Australian Plate subducting below the Eurasian Plate. It was caused by an earthquake measuring more than magnitude 9. The earthquake caused the seafloor to uplift, displacing the seawater above.

In open ocean the tsunami measured less than 1 metre high.

The tsunami travelled at speeds up to 800km per hour.

When the Tsunami reached the shores, the height of the wave increased to 15 metres in some areas.

Main impacts

A quarter of a million people died.

Two million people were made homeless.

People were swept away in the waters, which arrived rapidly and with little warning.

Thirteen countries were affected, the worst being Indonesia.

Indonesia was hit by the tsunami first. 45minutes later the tsunami reached Thailand.

Mangrove swamps helped to act as a barrier to reduce the energy of the water in some areas.

Short-term aid, such as water purification tablets, temporary housing and medical supplies were given from international countries.

Islands reliant on tourism and fishing, such as the Maldives, had to rebuild their industries.

An early warning system between countries surrounding the Indian Ocean has been set up.

Asian Tsunami, 2004

Volcanic Hazards

Definitionsand types of volcano

Pyroclastic flows : super heated flows of ash, cinders and pumice capable of travelling at speeds up to 160km and reaching temperatures up to 1000°C.

Lahars : mudflows caused by the combination of water with volcanic ash and dust

Shield volcanoes are usually found at constructive or tensional boundaries.They are low, with gently sloping sides.They are formed by eruptions of thin, runny lava.Eruptions tend to be frequent but relatively gentle.

Composite volcanoes are made up of alternating layers of lava and ash (other volcanoes just consist of lava).They are usually found at destructive or compressional boundaries.The eruptions from these volcanoes may be a pyroclastic flow rather than a lava flow. A pyroclastic flow is a mixture of hot steam, ash, rock and dust.A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of over 400°C

Impact of Earthquakes

Impacts of Earthquakes

Social impacts Economic impacts Environmentalimpacts

Short term impacts People may be killed or injured. Homes may be destroyed. Transport and communication links may be disrupted. Water pipes may burst and water supplies may be contaminated.

Shops and business may be destroyed. Looting may take place. The damage to transport and communication links can make trade difficult.

The built landscape may be destroyed. Fires can spread due to gas pipe explosions. Fires can damage areas of woodland. Landslides may occur.Tsunamis may cause flooding in coastal areas.

Long term impacts Disease may spread. People may have to be re-housed, sometimes in refugee camps.

The cost of rebuilding a settlement is high. Investment in the area may be focused only on repairing the damage caused by the earthquake. Income could be lost.

Important natural and human landmarks may be lost.

Factors affecting the damage caused

Factor Description

The strength of the earthquake and the number of aftershocks

• The stronger the earthquake the more damage it can do

• An earthquake of 6.0 on the Richter scale is ten times more powerful than of 4.0

Population density

• An earthquake that hits an area of high population density could inflict far more damage than an area of low density population

The types of buildings

• MEDC’s generally have better quality buildings that are more able to cope with vibrations from earthquakes

• They are also likely to have insurance.

The time of day• An earthquake in rush hour would be far more

dangerous than one in the middle of the night where less traffic is about.

The distance from the epicentre

• The closer to the epicentre, the more damage done.

The type of rock and sediment

• Loose material may act as a liquid when shaken.

The impacts of earthquakes can be reduced in a number of ways include:• Land use zoning • Building design• Stabilisation of

steep slopes• Improved

warning and predictions

The world’s worst earthquakes by death toll in the 20th

and 21st

century

Country Year Death toll Richter scale

Indonesia 2004 248 000 9.1

China 1976 242 149 7.5

China 1927 200 000 8.3

China 1920 180 000 8.6

Messina, Italy 1908 160 000 7.5

Tokyo, Japan 1923 142 800 7.9

Turkmenistan 1948 110 000 7.3

Kashmir, Pakistan 2005 86 000 7.6

China 1932 70 000 7.6

Chengdu, China 2008 69 000 7.9

Peru 1970 66 800 7.7

Iran 1990 50 000 7.7

Quetta, Pakistan 1935 45 000 7.7

Turkey 1932 32 000 7.8

Avezzano, Italy 1915 30 000 6.9

Bam, Iran 2003 30 000 6.6

Chile 1939 28 000 7.8

Iran 1978 25 000 7.7

Armenia 1988 25 000 6.8

Guatemala 1976 23 000 7.5

Factors affecting the impact of a volcano

Factor and solutions affecting the impact of a volcano

Factor Description

Type of eruption Runny basaltic lava eruptions result in less violent eruptions and generally less loss of life. For example, Mauna Loa in Hawaii. In contrast, explosive eruptions like Mount St Helens result in greater destruction of the environment, economy an loss of life.

Population density A volcanic eruption that hits an area of high population density could inflict far more damage than an area of low density population. For example, Pompeii.

Size of eruption The eruption in Krakatoa in 1883 was heard thousands of miles away whereas small scale eruptions and lava flows do not result in any loss of life.

Frequency of eruptions Frequent eruptions reduce the pressure in the magma chamber which reduces the likelihood of explosive eruptions and visa versa.

Solution Description

Monitoring and prediction

Vital to reducing the loss of life in a volcanic eruption. The Nyiragongo volcano in the Democratic Republic of Congo was not predicted where Mount St Helens was predicted. The ongoing monitoring of the Soufriere volcano means loss of future life will be limited.

Understanding secondary hazards

Some people are more at risk than others. One of the main secondary hazards of a volcanic eruption is lahars or mudflows. On Monserrat, lahars were concentrated in main valleys which directed the liquid in a certain direction

Volcanic Eruption Case Study

March 15th 1991: a succession of earthquakes was felt on the north-western side of the volcano.

Further earthquakes of increasing intensity were felt over the next two weeks.

April 2nd 1991, the volcano awoke.

The volcano had phreatic eruptions occurring near the summit along a 1.5 km long fissure.

Over the next few weeks, small eruptions continued, dusting the surrounding areas with ash.

Seismographs detected hundreds of small earthquakes every day.

Radiocarbon, dating of charcoal found in old volcanic deposits revealed the three major explosive eruptions in the recent millennia.

Geological mapping showed that much of the surrounding plains were formed by lahar deposits from previous eruptions

The measurements of Sulphur dioxide emission showed a rapid increase from 500 tonnes per day on May 13th to 5,000 tonnes per day by May 28th.

This implied that there was a rising column of fresh magma beneath the volcano.

After May 28th, the amount of Sulphur dioxide being emitted decreased substantially.

This raised fears that the degassing of the magma had been blocked somehow. Leading to a pressure build-up in the magma chamber and a high likelihood of explosive eruptions.

The first magma eruptions occurred on June 3rd.

The first large explosion was on June 7th,. Which generated an ash column 7 km high.

The Philippine Institute of Volcanology and Seismology issued a warning indicating the possibility of a major eruption within two weeks.

Mount Pinatubo Eruption 1991

Volcanic Eruption Case Study

Evacuation of Pinatubo

The volcanologists were under some pressure to deliver a timely and accurate assessment of the volcanic risk.

Three successive evacuation zones were defined:

The innermost containing everything within 10 km of the volcano's summit.

The second extending from 10 to 20 km from the summit.

And the third extending from 20 to 40 km from the summit.

The 10 km and 10–20 km zones had a total population of about 40,000 people.

While some 331,000 people lived in the 20–40 km zone.

Five stages of volcanic alert were defined, from level 1 which is a low level seismic disturbances up to level 5 which is a major eruption in progress.

Many of the Aeta who lived on the slopes of the volcano left their villages of their own volition when the first explosions began in April.

The Aeta gathered in a village about 12 km from the summit.

Mount Pinatubo Eruption 1991

Volcano Case Study

Montserrat is a small island in the Caribbean. There is a volcanic area located in the south of the island on Soufriere Hills called Chances Peak. Before 1995 it had been dormant for over 300 years. In 1995 the volcano began to give off warning signs of an eruption (small earthquakes and eruptions of dust and ash). Once Chances Peak had woken up it then remained active for five years. The most intense eruptions occurred in 1997.

During this time, Montserrat was devastated by pyroclastic flows. The small population of the island (11,000 people) was evacuated in 1995 to the north of Montserrat as well as to neighbouring islands and the UK.

Despite the evacuations, 19 people were killed by the eruptions as a small group of people chose to stay behind to watch over their crops.

Volcanic eruptions and lahars have destroyed large areas of Montserrat. The capital, Plymouth, has been covered in layers of ash and mud. Many homes and buildings have been destroyed, including the only hospital, the airport and many roads.

The graphic shows the progress of the eruption

and its impact on the island.

Short-term responses and results

Evacuation.

Abandonment of the capital city.

The British government gave money for compensation and redevelopment.

Unemployment rose due to the collapse of the tourist industry.

Long-term responses and results

An exclusion zone was set up in the volcanic region.

A volcanic observatory was built to monitor the volcano.

New roads and a new airport were built.

Services in the north of the island were expanded.

The presence of the volcano resulted in a growth in tourism.

Chances Peak, Montserrat, 1995-97

Hazard management and risk assessments

Ways of managing the consequences of a hazard

Modifying the hazard event, through building design, building location and emergency procedures.

Improved forecasting and warning – for example, it is difficult to predict earthquakes, although in some cases there may be a ‘recurrence interval’

Sharing the cost of loss, through insurance or disaster relief

The likely size and range of natural processes involved

The extent of the impacts

Ways in which the impacts can be reduced

Risk assessment

Managing disasters

Pre-disaster planning Post-disaster responses

Prevention: action to reduce the severity of impact

Response: effectiveness depends on education, training and experiences of emergency responses teams

Mitigation: actions to reduce property damage and minimise economic impacts

Recovery: action to assist communities to return to pre-disaster conditions

Preparedness: action to increase speed and efficiency responses

Redevelopment: action to manage economic losses; there should be a long term link between natural hazard and national economic activities

Physical adjustments Social adjustments

Building and construction techniques to withstand a hazard of given size and strength

Land-use zoning and restrictions for hazardous locations

Identifying and avoiding sites where hazardsare likely to occur

Spreading economic loss more fairly though insurance

Predicting where and when a hazard might occur

Public awareness through education

Preventing or altering characteristics Evacuation plans

Emergency preparedness

Issuing early warning signs