Natural Hazards and Natural Disasters

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  • 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 i

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