Natural Hazards

Introduction to Natural Hazards• What is a “Geohazard”?

– Earth processes (involving the lithosphere, hydrosphere & atmosphere) that, upon interaction with human activity, cause loss of life and property

– It is important to understand the human element• without it, there would be no hazard• because of it, the science of geohazards becomes more

important every year– mitigation: reduction/prevention

geo-process

humanprocess

Hazardousconditionor result

• The Earth’s population is increasing• more people living in hazard-prone areas• populations are becoming hyper-concentrated• consumption of resources• examples:

– today there are 6 billion people on Earth ( ~ 50% live in cities)

– by 2025, there will be ~8 billion people (~ 66% in cities)

– of these cities, 40% are coastal

» prone to severe storm and tsunami damage

– and a large majority lie in areas subject to other geohazards (for example volcanoes and earthquakes)

Why is the human element so critical?

•CANNOT stop the geologic processes•CANNOT stop the population growth/expansion

•Therefore, we must try to reduce (mitigate) the hazards through:

•scientific study•population education•changes in engineering/building practices•management plans and hazard response scenarios

Types of Natural Hazards• Volcanoes, floods, earthquakes,

tornadoes, tsunamis, etc.– can act adversely on human

processes– can occur:

• without warning (e.g. earthquakes)• with warnings (precursors) (e.g.

satellite monitoring of cyclone tracks, or the presence of ground deformation at a volcano before an eruption)

• To help mitigate the hazard we need to know:• Frequency vs. Magnitude

– F: how often a given event occurs in a certain region

– M: how powerful (amount of energy released) an event is

• for example, high M hazards happen with low F, but are much more destructive

• Scope– S: area affected by a given hazard

• local: landslides, floods, earthquakes, fire …• regional: tsunamis, volcanoes, larger earthquakes,

cyclones …• global: large volcanoes, global warming, meteorite

impacts …

Practical Exercise 1.

Impact of Environmental Disasters

Earthquakes and Tsunamis

What is an Earthquake? • Ground movement caused by the sudden

release of seismic energy due to tectonic forces.

The focus of an earthquake is the actual location of the energy released inside the Earth’s crust.

The epicentre is the point on the Earth’s surface directly above the focus.

Why do earthquakes occur?• Seismic energy is usually caused by the brittle

failure (fracturing) of rocks under stress.

• This commonly occurs due to movement along tectonic plate boundaries

Figure showing the distribution of earthquakes around the globe

Earthquake MagnitudeMagnitude Earthquake Effects Approx. number

each year< 2.5 Usually not felt, but recorded 900,000

2.5-5.4 Often felt, only minor damage 30,000

5.5-6.0 Slight damage to buildings and other structures

500

6.1-6.9 May cause a lot of damage in very populated areas

100

7.0-7.9 Major earthquake. Serious damage.

20

> 8.0 Great earthquake. Can be totally destructive near the epicentre.

1 every 5-10 years

San Francisco - Great Earthquake

• Magnitude 7.7 - 8.3

Earthquake Hazards• These are important hazards to understand:

– the natural hazard that on average kills the highest number of people per year (> 1 million during the past century)

– commonly strikes without warning – no time for evacuation – not a predictable trend to earthquake numbers,

magnitude or location • 1000's of large earthquakes every year • ~ 20 are > M7.0 and these account for 90% of the energy

released and 80% of all the fatalities

How do we mitigate the hazard from earthquakes?

• Reinforce buildings

• Education

• Disaster plan

Earthquakes and Tsunami’s• An earthquake under the ocean has the

potential to form a tsunami.

• The earthquake must vertically displace overlying water (extensional or compressional faults - not transform)

Extension CompressionTransform

How does an earthquake form a tsunami?

2004 South Asian Boxing Day event

• Biggest earthquake in 40 years!

• Magnitude 9.2• 150 km off the west

of Northern Sumatra

• Generated a disastrous tsunami in 12 countries

• The earthquake occurred at a convergent tectonic plate boundary (subduction zone)

• An estimated 1,600 km (994 miles) of faultline slipped about 15 m (50 ft)!

• The earthquake released 20 x 1017 Joules of energy– Equivalent to:

• 475,000,000 kg of TNT• 23,000 Hiroshima atomic bombs!

Second largest recorded earthquake

Tsunami

Animations of the Boxing Day tsunami showing how the tsunami radiated from the entire length of the 1,600 km (994 miles) rupture.

Above: Countries most effected by the tsunami

A village near the coast of Sumatra lays in ruin after the tsunami.

How do we mitigate the hazard from tsunamis?

• Monitoring– process is very technology-

intensive• high costs for many poorer

countries

– often no technology available to monitor local tsunamis

• for example,• Papua New Guinea has no

monitoring stations– reliant on the Pacific Tsunami

Warning Center

• tsunami in 1998 was not detected

• Building restrictions in hazard prone areas – In Hawaii, Hilo harbor and

downtown was destroyed by the tsunamis of 1946 and 1960

– The town is now rebuilt on higher ground and the devastated area is a park

How do we mitigate the hazard from tsunamis?

• Seawall construction – cause early wave breaking– prevent wave run up into urban areas

How do we mitigate the hazard from tsunamis?

• Education– warning systems– evacuation plans– general understanding

of the hazards involved

PunishmentPunishmentFrom God From God

45%45%

Natural eventNatural event35%35%

Bomb 20%Bomb 20%Population reaction: Papua New Guinea (1998)

How do we mitigate the hazard from tsunamis?

Practical Exercise 2.

Locating Earthquake Epicentres

Tropical Storms

Same Storm - Different Name

Tropical Cyclones• Background:

– Can be deadly!• For example, in 1991 a large

cyclone in Bangladesh killed >138,000 people in just two days!

• Most widespread destructive weather hazard – For example: Hurricane

Floyd (1999) • only a moderate level

hurricane

• caused US$5.6 billion in damage in the Bahamas and North Carolina (USA) and 57 fatalities

Tropical Cyclones

(Left) Three different cyclones spinning over the western Pacific Ocean on August 7, 2006.

How do cyclones form?

The above figure shows how cyclones form. The green arrows show

where warm air is rising. The red arrows indicate where cool air is sinking.

Cyclone CategoriesCategory Wind Speed

(mph)Damage at

LandfallStorm Surge

(feet)

1 74-95 Minimal 4-5

2 96-110 Moderate 6-8

3 111-130 Extensive 9-12

4 131-155 Extreme 13-18

5 > 155 Catastrophic 19+

The Saffir-Simpson Hurricane Scale

Hurricane Katrina

• Hurricane Katrina was the most costly and most deadly hurricane in the history of the USA.– Category 5

• At least 1,836 fatalities

• Damage estimated at US$ 81.2 billion

Hurricane Katrina

What damage is produced?• Storm Surge

– water that is pushed toward the shore by the force of the cyclone winds.

What damage is produced?

• Wind– responsible for the

loss of power and utilities

– wind damage affects larger areas than surge

– flying debris– tree loss

What damage is produced?

• Flying debris– debris

propelled at high speeds

How do we mitigate the hazard from a cyclone?

• Monitoring– early warning systems

• Infrastructure– cyclone walls– communal shelters

• Education and planning

Natural Hazards Summary

Graph showing the number of deaths per year due to natural hazard events

HAZARDDamage Potential

Awareness- Effect on Elements

Society

Quicker Recovery

ActionPlans Communities

MoreResilient

Huge Losses/Damages

ReducedLosses

Elements at Risk

More Stable Society

HAZARDDamage Potential

Elements at Risk

Slopes of hills

Sea & Sea-coast

Low-lying Areas

River/Stream Banks

Natural Features

Unsecured personal assetsLivelihood tools / Equipment

Public Infrastructure

Agri. & Horticultural crops

Weak Buildings

Huts & Semi-permanent Houses

People & Live-stock

Societal Elements

CYCLONEDamage Potential

SocietyPoorer than

before

Disruption ofNormal life & DevelopmentSuffers

Huge Losses/Damages

Elements at Risk

Major natural disasters:   •   Flood

• Cyclone• Drought

• Earthquake

Minor natural disasters: • Cold wave

• Thunderstorms• Heat waves• Mud slides

• Storm

Major manmade disaster: 1. Setting of fires

2. Epidemic 3. Deforestation

4. Pollution due to prawn cultivation

5. Chemical pollution. 6. Wars

 

Minor manmade disaster:• Road / train accidents, riots

• Food poisoning • Industrial disaster/ crisis• Environmental pollution

    

Types of disasters

Scale of DisasterIs Dependent on :• Lead Time Available.• Intensity of Hazard.• Duration.• Spatial Extent.• Density of Population & Assets.• Time of Occurrence.• Vulnerabilities existing in the

Elements at Risk.

•Hazard X Vulnerability = Disaster

ELEMENTS AT RISK• People• Livestock• Rural Housing Stock• Houses Vulnerable• Crops, Trees,Telephone, Electric

poles• Boats, Looms, Working Implements• Personal Property• Electricity, Water and Food Supplies• Infrastructure Support

AIMS OF DISASTER MANAGEMENT

• Reduce (Avoid, if possible) the potential losses from hazards.

• Assure prompt and appropriate assistance to victims when necessary.

• Achieve rapid and durable recovery.

 

 

DURING DISASTER

DISASTER MANAGEMENT CYCLE

PRE-DISASTER                 

 

PO

ST

- D

ISA

ST

ER

 

Stages of DisasterCyclone

Well Before Weeks-Months

Just Before - Hours

Actual Time Period

Rescue Rehabilitation Relief Reconstruction

BEFORE AFTERDURING

Jan - Apr MAY June- Oct

Role Players in Disasters• People : Individuals, House -Holds,

Volunteers• Gram Panchayat : Sarpanch, Panchayati Secretary, Panchayati Members• Village Elders : Caste/Community/Religious Leaders, Teachers, Doctors, Engineers, Retired Army & Police Personnel• Govt. Deptl. Officers : Agriculture, Medical, Engineers (Housing, Roads & Buildings, Irrigation) Revenue Department, Public Health, Police etc. NGOs

DEFINITIONS OF “VULNERABILITY”

• “The extent to which a community, structure, service or geographic area is likely to be damaged or disrupted by the impact of particular disaster hazard…”

• “Vulnerability is the propensity of things to be damaged by a hazard”.

DISASTER PREPAREDNESS

• Disaster preparedness aims at minimizing the adverse effects of a hazard -

• Through effective precautionary actions

• Ensure timely, appropriate and efficient organisation and delivery of emergency response following the impact of a disaster.

PREPAREDNESS• Vulnerability Analysis and Mapping to

include Resources.• Assess strengthening requirements and

execute.• Funding for preparedness must be

arranged.• Peoples’ cooperation through Political

leaders, elders, Volunteers and NGOs• Create lead time by interpreting Warnings• Plan to include movement of resources

with time frame.• Aim to reduce the destructive potential of

cyclones, timely & appropriate relief to victims and quick & durable recovery

Disaster Preparedness Framework

Rehearsals Public Education

and Training

Response Mechanisms

Warning Systems

Resource Base

Information System

Institutional Framework

PlanningVulnerability Assessment

COMPONENTS OF PREPAREDNESS

Disaster Response Activities

• Warning • Evacuation/Mitigation• Search and Rescue• Assessment• Emergency Relief• Logistics and Supply• Communication and information

Management • Survivor Response and coping• Security• EOC & coordination• Expedite rehabilitation and

reconstruction.

Floods and Water Hazards

Elements at Risk• Everything in

the flood plain.• Earthen or

soluble structures

• Buried services and utilities

• Food stores• Crops and

livestock

Main Mitigation Strategies.

• Land use control• Engineering of

strictures• Elevation of

structures• Flood control

structures• Reforestation

projects (watershed management)

Strong Winds

Elements at Risk

• Lightweight structures.

• Elevated utilities (Power and communication lines)

• Fishing boats and other maritime industries.

Main Mitigation Strategies.

• Structural engineering measures.

• Planting of windbreaks.