Natural Hazards and Natural Disasters

8/11/2019 Natural Hazards and Natural Disasters

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EENS 3050 Natural Disasters

Tulane University Prof. Stephen A. Nelson

Natural Disasters & Assessing Haar!s an! "is#

This page last updated on 20-Aug-2013

Natural Hazards and Natural Disasters

A natural hazard is a threat of a naturally occurring event will have a negative effect onhumans. This negative effect is what we call a natural disaster. In other words when the

hazardous threat actually happens and harms humans we call the event a natural disaster.

!atural "azards #and the resulting disasters$ are the result of naturally occurring processes that

have operated throughout %arth&s history.

'ost hazardous process are also (eologic )rocesses.

(eologic processes effect every human on the %arth all of the time *ut are most

noticea*le when they cause loss of life or property. If the process that poses the hazardoccurs and destroys human life or property then a natural disaster has occurred. Among

the natural hazards and possi*le disasters to *e considered are+

%arth,uaes

olcanic %ruptions

Tsunami

/andslides

u*sidence

loods

roughts

"urricanes

Tornadoes

Asteroid Impacts

All of these processes have *een operating throughout %arth history *ut the processes

have *ecome hazardous only *ecause they negatively affect us as human

*eings. Important Point -There would be no natural disasters if it were not for

humans. Without humans these are only natural events.

is is characteristic of the relationship *etween humans and geologic processes. 4e

all tae riss everyday. The ris from natural hazards while it cannot *e eliminated can

in some cases *e understood in a such a way that we can minimize the hazard to

humans and thus minimize the ris. To do this we need to understand something a*out

the processes that operate and understand the energy re,uired for the process. Then we

can develop an action to tae to minimize the ris. uch minimization of ris iscalled hazard mitigation.


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Although humans can sometimes influence natural disasters #for e5ample when poor

levee design results in a flood$ other disasters that are directly generated *y humans

such as oil and to5ic material spills pollution massive automo*ile or train wrecs

airplane crashes and human induced e5plosions are considered technological disasters

and will not *e considered in this course e5cept when they occur as a secondary result

of a natural disaster.

ome of the ,uestions we hope to answer for each possi*le natural disaster are+

4here is each type of hazard liely to *e present and why6

4hat scientific principles govern the processes responsi*le for the disasters6

"ow often do these hazards develop into disasters6

"ow can each type of disaster *e predicted and7or mitigated6

As discussed *efore natural disasters are produced *y processes that have *een operating since

the %arth formed. uch processes are *eneficial to us as humans *ecause they are responsi*lefor things that mae the %arth a ha*ita*le planet for life. or e5ample+

Throughout %arth history volcanism has *een responsi*le for producing much of the

water present on the %arth&s surface and for producing the atmosphere.

%arth,uaes are one of the processes responsi*le for the formation of mountain ranges

which which direct water to flow downhill to form rivers and laes.

%rosional processes including flooding landslides and windstorms replenishes soil and

helps sustain life.

Such processes are only considered hazardous when they adversely affect humans and

their activities.

Classification of Natural Hazards and Disasters

!atural "azards and the natural disasters that result can *e divided into several different

categories+

(eologic "azards - These are the main su*8ect of this course and include+

%arth,uaes

olcanic %ruptions

Tsunami

/andslides

loods

u*sidence

Impacts with space o*8ects

Atmospheric "azards - These are also natural hazards *ut processes operating in the

atmosphere are mainly responsi*le. They will also *e considered in this course and

include+

Tropical 9yclones

Tornadoes roughts

evere Thunderstorms


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/ightening

:ther !atural "azards - These are hazards that may occur naturally *ut don&t fall in to

either of the categories a*ove. They will not *e considered to any great e5tent in this

course *ut include+

Insect infestations

isease epidemics

4ildfires

!atural "azards can also *e divided into catastrophic hazards which have devastating

conse,uences to huge num*ers of people or have a worldwide effect such as impacts with

large space o*8ects huge volcanic eruptions world-wide disease epidemics and world-wide

droughts. uch catastrophic hazards only have a small chance of occurring *ut can have

devastating results if they do occur.

!atural "azards can also *e divided into rapid onset hazards such as olcanic %ruptions

%arth,uaes lash floods /andslides evere Thunderstorms /ightening and wildfires whichdevelop with little warning and strie rapidly.Slow onset hazards lie drought insect

infestations and disease epidemics tae years to develop.

Anthropoenic Hazards

These are hazards that occur as a result of human interaction with the environment. They

includeTechnological Hazards which occur due to e5posure to hazardous su*stances such as

radon mercury as*estos fi*ers and coal dust. They also include other hazards that have formed

only through human interaction such as acid rain and contamination of the atmosphere or

surface waters with harmful su*stances as well as the potential for human destruction of the

ozone layer and potential glo*al warming.

!ffects of Hazards

"azardous process of all types can have primary secondary and tertiary effects.

Primary Effectsoccur as a result of the process itself. or e5ample water damage during

a flood or collapse of *uildings during an earth,uae landslide or hurricane.

Secondary Effectsoccur only *ecause a primary effect has caused them. or e5ample

fires ignited as a result of earth,uaes disruption of electrical power and water service as

a result of an earth,uae flood or hurricane or flooding caused *y a landslide into alae or river.

Tertiary Effectsare long-term effects that are set off as a result of a primary event. These

include things lie loss of ha*itat caused *y a flood permanent changes in the position of

river channel caused *y flood crop failure caused *y a volcanic eruption etc.

"ulnera#ility to Hazards and Disasters

ulnera*ility refers the way a hazard or disaster will affect human life and property

ulnera*ility to a given hazard depends on+

)ro5imity to a possi*le hazardous event


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)opulation density in the area pro5imal to the event

cientific understanding of the hazard

)u*lic education and awareness of the hazard

%5istence or non-e5istence of early-warning systems and lines of communication

Availa*ility and readiness of emergency infrastructure

9onstruction styles and *uilding codes

9ultural factors that influence pu*lic response to warnings

In general less developed countries are more vulnera*le to natural hazards than are

industrialized countries *ecause of lac of understanding education infrastructure *uilding

codes etc. )overty also plays a role - since poverty leads to poor *uilding structure increased

population density and lac of communication and infrastructure.

"uman intervention in natural processes can also increase vulnera*ility *y

evelopment and ha*itation of lands suscepti*le to hazards or e5ample *uilding on

floodplains su*8ect to floods sea cliffs su*8ect to landslides coastlines su*8ect to

hurricanes and floods or volcanic slopes su*8ect to volcanic eruptions.

Increasing the severity or fre,uency of a natural disaster. or e5ample+ overgrazing ordeforestation leading to more severe erosion #floods landslides$ mining groundwater

leading to su*sidence construction of roads on unsta*le slopes leading to landslides or

even contri*uting to glo*al warming leading to more severe storms.

Affluence can also play a role since affluence often controls where ha*itation taes place for

e5ample along coastlines or on volcanic slopes. Affluence also liely contri*utes to glo*al

warming since it is the affluent societies that *urn the most fossil fuels adding 9:2to the

atmosphere.

Assessin Hazards and $is%

"azard Assessment and is Assessment are2 different concepts;

Hazard Assessmentconsists of determining the following when and where hazardous processes have occurred in the past.

the severity of the physical effects of past hazardous processes #magnitude$.

the fre,uency of occurrence of hazardous processes.

the liely effects of a process of a given magnitude if it were to occur now.

and maing all this information availa*le in a form useful to planners and pu*lic

officials responsi*le for maing decisions in event of a disaster.

$is% Assessmentinvolves not only the assessment of hazards from a scientific point of view

*ut also the socio-economic impacts of a hazardous event. is is a statement of pro*a*ility thatan event will cause 5 amount of damage or a statement of the economic impact in monetary

terms that an event will cause. is assessment involves

hazard assessment as a*ove

location of *uildings highways and other infrastructure in the areas su*8ect to hazards

potential e5posure to the physical effects of a hazardous situation

the vulnera*ility of the community when su*8ected to the physical effects of the event.

is assessment aids decision maers and scientists to compare and evaluate potential hazards

set priorities on what inds of mitigation are possi*le and set priorities on where to focus

resources and further study.


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Prediction and &arnin

is and vulnera*ility can sometimes *e reduced if there is an ade,uate means of predicting a

hazardous event.

Prediction

)rediction involves+

A statement of pro*a*ility that an event will occur *ased on scientific o*servation

uch o*servation usually involves monitoring of the process in order to identify some

ind ofprecursor event(s)- an anomalous small physical change that may *e nown to

lead to a more devastating event. - %5amples+

"urricanes are nown to pass through several stages of development+ tropical

depression - tropical storm - hurricane. :nce a tropical depression is identified

monitoring allows meteorologists to predict how long the development will tae

and the eventual path of the storm. olcanic eruptions are usually preceded *y a sudden increase in the num*er of

earth,uaes immediately *elow the volcano and changes in the chemical

composition of the gases emitted from a volcanic vent. If these are closely

monitored volcanic eruptions can *e often *e predicted with reasona*le

accuracy.

'orecastin

ometimes the word


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responsi*le for taing action in the event of a potential disaster will not respond.

're(uency of Natural Disasters

Again it is important to understand that natural disasters result from natural processes that

affect humans adversely.'irst - Size )atters

or e5ample+

"umans coe5ist with rivers all the time and *enefit from them as a source of water and

transportation. :nly when the volume of water in the river *ecomes greater than the

capacity of the stream channel is there a resulting disaster.

mall earth,uaes occur all of the time with no adverse effects. :nly large earth,uaes

cause disasters.

Second * +ocation, location, location

or e5ample+

A volcanic on an isolated uninha*ited island will not result in a natural disaster.

A large earth,uae in an unpopulated area will not result in a disaster.

A hurricane that maes landfall on a coast where few people live will not result in a

disaster.

o what we have to worry a*out is large events that strie areas where humans live.

Thus in natural hazards studies it is important to understand the relationship *etween

fre,uency of an event and the size of the event. ize is often referred to a magnitude.

or 8ust a*out any event statistical analysis will reveal that larger events occur less fre,uently

than small events.

tatistical analysis of some types of events for specific locations allow one to determine

the return periodor recurrence interval.

%5amples+


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Flood Frequency-

or any river high

discharge events are rare.

/arge discharge events

occur much less

fre,uently than smalldischarge events.

Meteorite Impacts -

Although we as humans have not had the opportunity #fortunately$ of o*serving large asteroidor meteorite impacts the data suggest that impacts of large asteroids #1 m or larger$ occurs

only once every 10 million years.

Earthquakes-

As we have 8ust noted large earth,uaes occur much less fre,uently than smaller earth,uaes.

Those with magnitudes greater than ?. only occur once every 3 years on the average #see Ta*le

3.3 in your te5t or http+77www.iris.edu7h,7gallery7photo710CC$
http://www.iris.edu/hq/gallery/photo/1066http://www.iris.edu/hq/gallery/photo/1066


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Is the 're(uency of Natural Disasters Increasin

Are natural disasters *ecoming more fre,uent as it seems from news reports of recent activity6

The short answer appears to *e that yes natural disasters are increasing in fre,uency

#seehttp+77maps.grida.no7go7graphic7trends-in-natural-disasters. Dut this suggests some other

important ,uestions *efore we start maing conclusions a*out the end of the world+

1. Is the fre,uency of hazardous events increasing62. 4hy is the fre,uency of natural disasters increasing #what could e5plain the trend$6

irst Is the fre,uency of hazardous events increasing6 This is much more difficult to answer

since natural events responsi*le for natural disasters have *een occurring throughout the E.

*illion year history of the %arth. !evertheless there is no evidence to suggest that hazardous

events are occurring more fre,uently.

4hat a*out glo*al warming6 There is evidence to suggest that weather related disasters are

*ecoming more fre,uent compared to other disasters lie earth,uaes. or e5ample the

fre,uency of disasters from tropical cyclones and floods has *een increasing the fre,uency of

earth,uaes has changed little. Although this is what we e5pect from glo*al warming there is

not yet enough statistical data to prove this right now.

econd is there another e5planation for the the fre,uency of natural disasters increasing6 irst

consider the following facts+

"uman population has *een increasing at an e5ponential rate. 4ith more people vulnera*ility

increases *ecause there are more people to *e affected *y otherwise natural events.

"uman population is moving toward coastal areas #seehttp+77www.livescience.com7E1C=-

flocing-coast-world-population-migrating-danger.html$. These are areas most vulnera*le to

natural hazards such as tropical cyclones tsunami and to some e5tent earth,uaes.

:ur a*ility to communicate news of natural disasters has *een increasing especially since the

invention of the internet. %arlier in human history there may have *een 8ust as many disasters

*ut there were few ways the news of such disasters could *e communicated throughout the

world.

'eanwhile+

eaths from natural disasters has decreased in developed countries and increased in developing

countries. 4hat could e5plain this6 )olitics6 %conomics6 9ultural ifferences6 %ducation6

The cost of natural disasters has *een increasing in developed countries. 4hat could e5plain

this6 %conomics6

his Course

This course is nota*out the political cultural or economic aspects of natural disasters.

It is a*out the science of natural disastersand how can use our nowledge of the scientific

aspects of disasters to reduce the death and destruction caused *y otherwise natural events.

!/amples of (uestions on this material that could #e as%ed on an e/am

1. efine and give e5amples of each of the following types of hazard #a$ geologic hazard#*$ atmospheric hazard #c$ catastrophic hazard #d$ rapid onset hazard #e$
http://maps.grida.no/go/graphic/trends-in-natural-disastershttp://maps.grida.no/go/graphic/trends-in-natural-disastershttp://www.livescience.com/4167-flocking-coast-world-population-migrating-danger.htmlhttp://www.livescience.com/4167-flocking-coast-world-population-migrating-danger.htmlhttp://www.livescience.com/4167-flocking-coast-world-population-migrating-danger.htmlhttp://maps.grida.no/go/graphic/trends-in-natural-disastershttp://www.livescience.com/4167-flocking-coast-world-population-migrating-danger.htmlhttp://www.livescience.com/4167-flocking-coast-world-population-migrating-danger.html


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anthropogenic hazard #f$ slow oneset hazard .

2. %5plain how poverty and affluence can play a role in increasing vulnera*ility to natural

hazards.

3. 4hat is the difference *etween hazard assessment and ris assessment6

E. 4hat factors determine the effectiveness of warning systems6

. %5plain the difference *etween primary secondary and tertiary effects of possi*le

hazards.

C. 4hat is the relationship *etween size of natural events disasters and fre,uency of

disasters6 4hat is the concept of recurrence interval6

=. 4hat might *e responsi*le for the apparent increase in recent years of the num*er of

natural disasters and the economic losses due to natural disasters6

Documents

Natural Hazards and Natural Disasters