NATURAL HAZARDS AND DISASTERS:ORIGINS, RISKS,

MITIGATION AND PREDICTION

Manfred Koch

Department of Geohydraulics and Engineering Hydrology,University of Kassel

Kurt-Wolters Str.3, D-34109 Kassel, Germany E-mail: kochm@uni-kassel.de

Keywords: Natural hazards, disasters, earthquakes, volcanic eruptions, landslides, tsunamis, vulnerability, risk, disaster reduction, prevention, mitigation,

prediction

Recent natural disasters, Summer 2000

Floods in Bangladesh, India, China, Cambodia and parts of Ethiopia,mudflows in Austria, droughts in various countries of Africa, wildfires inSpain and the US, earthquakes in Mexico, Sachsen, eruption of a longdormant volcano in Japan, opening of the hurricane season in the south-eastern US and the Caribbean countries with a prediction of several majorhurricanes for the next months.

The $100 million question:

Has the occurence of disasters increased in the last decades?Or is this only an impression stemming from increased media presence?

Overview

1. Introduction

2. Natural hazards: Definitions, concepts, assessment, prediction 2.1 Categories and energy sources of natural hazards and disasters 2.2 Effects of Hazards 2.3 Vulnerability and Susceptibility 2.4 Hazard and Risk Assessment 2.5 Disaster (risk) reduction by early warning, prediction and forecasting

3. Earthquakes 3.1 Causes and effects 3.2 Global distribution 3.3 Quantification of seismic destruction 3.4 Seismic risk analysis and earthquake prediction

Overview (continued)

4. Volcanoes 4.1 Global distribution and characteristics 4.2 Volcanic Hazards 4.3 Prediction of volcanic activity

5 Landslides 5.1 Causes 5.2 Occurrence and effects 5.3 Prediction of landslides

6 Tsunamis 6.1 Causes, occurrences and effects 6.2 Early warning of tsunamis

7. Conclusions

1. Introduction: International Decade of Natural Disaster Reduction (IDNDR, 1990-2000)

"....The aim of this decade is to reduce through concerted international actions,especially in developing countries, loss of life, property damage and social andeconomic disruption caused by natural disasters ... and ... its goals are :

(a) To improve the capacity of each country to mitigate the effects of natural disasters

(b) To devise appropriate guidelines and strategies for applying existing knowledge,taking into account the cultural and economic diversity among nations;

(c) to foster scientific and engineering endeavours aimed at closing critical gaps inknowledge

(d) to disseminate existing and new information for the assessment, prediction,prevention and mitigation of natural disasters

(e) To develop measures for the assessment, prediction, prevention and mitigation ofnatural disasters through programs of technical assistance and technologytransfer...."

1. Introduction

Losses from natural disasters over the timeperiod 1965-1990 (After Berz 1992)

Insurance losses between 1987 and 1999

1. Introduction: Individual insured losses of circa US$1 billion and above resulting from natural disasters since 1987

Event: insured loss (US$ billions)Storms - Europe 1987 3.5 Hurricane Hugo 1989 4.5Earthquake - Loma Prieta - United States 1989 2Storms - Europe (2 storms) 1990 10Typhoon Mireille - Japan 1991 15California Fire Storm - United States 1991 1.7Hurricane Andrew 1992 17Storms - United States 1993 1.75Flooding (Mississippi) - United States 1993 1Storms - United States 1994 1.65Earthquake - Northridge - United States 1994 12.5Storms/Flooding - Europe 1995 1Storms - United States 1995 1.4Hurricane Opal 1995 2.1Earthquake - Kobe -Japan 1995 2.5Hurricane Fran 1996 1.6Ice Storm - Canada/United States 1998 1.15Hurricane Georges 1998 3.5Tornadoes - United States 1999 1.5Typhoon Bart - Japan 1999 2.2Hailstorm - Australia 1999 1.1Hurricane Floyd - USand the Bahamas 1999 1.8Earthquake - Taiwan 1999 1Storms - Europe 1999 6.8Earthquake - Turkey 1999 12??

1. Introduction: Major natural disasters in documented history

Location, Date Disaster Fatalities--------------------------------------------------------------------------------------------------- Pompei, 79: Volcanic eruption 20000 Costantinopole, 542: Bubonic plague Genoa, 1347-49 Bubonic plague one third of European populatipn

Shansi, China, 1556 Earthquake 830,000 Sevilla, Spain, 1649: Plague 80,000 Lisbon, 1755: Earthquake and tsunami 30,000 Philadelphia, 1793: Yellow fever epidemic 5,000 Indonesia, 1883: Tsunami 36,000 Japan, 1896: Tsunami 27,000 Galveston, 1900: Hurricane 8000 Mt Pelee, 1902 Volcanic eruption 29,000 San Francisco, 1906: Earthquake and fire Messina, Italy, 1908: 7.5 Earthquake 70,000 Mexico City, 1911: Earthquake Worldwide, 1918: Influenza pandemic 25 million Gansu, China, 1920: 8.6 Earthquake 200,000 Yokohama, 1923: 8.3 Earthquake 143,000 Nanshan, China, 1927: 8.3 Earthquake 200,000 Gansu, China, 1932: 7.6 Earthquake 70,000 Quetta, Pakistan, 1935: 7.5 Earthquake 30,000 Turkey, 1939: Earthquake 33,000

1. Introduction: Major natural disasters in documented history (after 1950)

Location, Date Disaster Fatalities----------------------------------------------------------------------------------------

West Iran, 1968: 7.3 Earthquake 7,000 North Peru, 1970: 7.8 Earthquake 66,000 Tangshan, China, 1976: 6.4 Earthquake 650,000 Andhra, India, 1977: Cyclone 10,000 West Iran, 1976: 6.5 Earthquake 15,000 Mexico City, 1985 6.8 Earthquake 8,000 Armenia, 1988: Earthquake 25,000 West Iran, 1990: 6.4 Earthquake 50,000 Latur, India, 1993: Earthquake 22,000 Kobe, Japan, 1995: Earthquake 6,500 New Guinea, 1998: Tsunami 3,000 Yangtze China, 1998: Flooding 3,600 Central America, 1998: Hurricane Mitch 12,000 Turkey, 1999: Earthquake >17,000 Taiwan, 1999: 7.6 Earthquake 1,800 Orissa, India, 1999: Cyclone 7,600 Venezuela, 1999: Floods >15,000

2. Natural hazards: Definitions, concepts, assessment, prediction2.1 Categories and energy sources of natural hazards and disasters

(a) Geologic hazards: Earthquakes, volcanic eruptions, tsunamis, landslides, floods, subsidence, impacts with meteorites (demise of the

dinosaurs, at the end of Cretaceous era, 60 my ago)

(b) Hydrometeorological hazards: Hurricanes, cyclones, tornadoes, floods, droughts, understorms, lightning

(c) Diseases and wildfires

Energy triggering these processes comes from

(a) the earth's internal heat generated primarily from radioactive break down of elements within the Earth. Drives earthquakes and volcanoes.

(b) solar energy derived primarily from the fusion of hydrogen into helium. This source of energy drives the earth's weather and ocean currents.

(c) gravitational energy which works with the two sources above to produce convection currents, flood currents, lahars, landslides and subsidence.

2.2 Effects of Hazards

(a) Primary effects are a result of the process itself. For example, water damage due to a flood, and collapse of buildings due to an earthquake, landslide, hurricane.

(b) Secondary effects are a result of a primary effect. For example, fires ignited byearthquakes or volcanic eruptions, disruption of electrical power and water serviceafter an earthquake or flood, and coastal flooding caused by a tsunami triggered byan earthquake---the high death toll of the 1755 Lisboa earthquake is mainly aconsequence of a high tsunami flood waver gushing over the lower-lying area of thecity---, or a flood generated by a landslide moving into a lake or river. The huge deathtoll of the 1976 Tangshang seism is also due to secondary effect of peopledrowning after the dikes of the high lying Yellow River had broken.

(c) Tertiary effects are long-term effects set off as a result of a primary event. Forexample, loss of habitat caused by a flood, permanent changes in the position ofriver channel caused by flood, crop failure caused by a volcanic eruption etc.

2.3 Vulnerability and Susceptibility

Hazardous geological processes are only threatening and may become a naturaldisaster when they adversely affect humans and their activities

<===> vulnerability

Vulnerability to a given hazard depends on factors, such as

(1) proximity to a possible hazardous event; (2) population density in the area close to the event; (3) scientific understanding of the hazard; (4) public education and awareness of the hazard; (5) existence of early-warning systems and lines of communication; (6) availability and readiness of emergency infrastructure; (7) construction styles and building codes and (8) cultural factors that influence the public response to warnings

2.3 Vulnerability and susceptibility (statement of the General Secretary of the UN (1999))

„ ....Most disaster victims of natural disasters live in developing countries, where poverty and population pressures force growing numbers of people to live in harm's way. We know why the trend is upward. Ninety per cent of disaster victimsworldwide live in developing countries, where poverty and population pressures forcegrowing numbers of poor people to live in harm's way --on flood plains, in earthquake-prone zones and on unstable hillsides. Unsafe buildings compound the risks. Thevulnerability of those living in risk-prone areas is perhaps the single most importantcause of disaster casualties and damage. Second, we know that unsounddevelopment and environmental practices exacerbate the problem. Massive loggingoperations and the destruction of wetlands reduce the soil’s ability to absorb heavyrainfall, making erosion and flooding more likely. Given that the pressures of povertyand population growth continue to increase, the disaster trend is likely to worsen if we do not take disaster prevention more seriously....“.

2.4 Hazard and Risk Assessment

Hazard assessment is based on geological and geophysical scientific processes andconsists of determining

(1) when and where hazardous processes have occurred in the past (2) the severity of the physical effects of past hazardous processes (3) the frequency of occurrence of hazardous processes (4) the likely effects of a process of a given magnitude if it would occur now(5) making all this information available for disaster emergency plans.

Risk assessment, is the ultimate processes of interests to the public to theinsurance companies. Consists in the evaluation of the probability that a hazardousevent will cause a certain amount of damage. It involves (1) hazard assessment, as above (2) location of buildings, highways in the areas subject to hazards (3) potential exposure to the physical effects of a hazardous situation (4) the vulnerability of the population when subjected to a disaster

2.4 Hazard and risk assessment (generation of risk)

Hazards, location, exposure, vulnerability and risk

Effect of population increase on disaster occurrence

2.5 Disaster (risk) reduction by early warning, prediction and forecasting

Major objective of the IDNDR 1990-2000:

"...reduce the loss of life, property damage, and social and economic disruptioncaused by natural disasters, through concerted international action, especially indeveloping countries...".

The fundamental importance of early warning for realizing this objective of disasterreduction was soon declared the most important programme target of the IDNDR.By drawing on global scientific knowledge and practical experience, the IDNDR‘sadvisory committee encouraged all countries to ensure the ready access to global,regional, national and local warning systems as part of their own national plans. From a scientific point of view the IDNDR‘s request for early warning necessitates the prediction and/or forecasting of a disaster. Although the two terms are often usedconcurrently, prediction is mostly employed for the long term forecasting of geologicaldisasters, such as earthquakes or volcanic eruptions, whereas for the short-termprediction of hydro-meteorologic hazardous events, such as torrential rains, hurricanes and floods, the word forecast is usually employed.

3. Earthquakes3.1 Causes and effects

Generation of an earthquake and ofseismic waves after rupture of a fault

Typical seismogram with P-, S- and surface waves

3. Earthquakes3.1 Causes and effects (San Andreas Fault)

3. Earthquakes3.1 Causes and effects (the 1995 Kobe, Japan earthquake)

3.2 Occurence and global distribution (subduction zones and mid-oceanic ridges)

3.2 Occurence and global distribution (seismics events 1954-1998)

3.2 Occurence and global distribution (plates and stresses)

Plates and their relative movements

Tectonic stress due to the collision of theAfrican and European plate

3.2 Occurence and global distribution (Germany) (events >M=3)

3.3 Quantification of seismic destruction

Ground motion (shaking) from the passage of seismic waves is at the primary originof earthquake damage at a certain location. The intensity of ground motiondepends on

(1) strength (intensity, magnitude, moment) of the earthquake (duration of ground motion depends also on these factors)

(2) distance from focus

(3) local geology (soil constitution of the underground)

(4) period (frequency) of the seismic waves

triggers resonance of the natural frequency (or period) of the soil formation or, even worse, of the buildings.

T= 0.1, 0.5 and 1-2 sec for a 1 , 4-5 and 10-20 story building, respectively

3.3.1 Intensity, magnitude and moment of an earthquake

Intensity Characteristic Effect Richter Scale Equivalent--------------------------------------------------------------------------------------------------------------------------------I People do not feel any earth movement <3.4II A few people notice movement if at rest 3.4-3.8 III People indoors feel movement. Hanging objects swing back and forth 3.9- 4.8IV Dishes, indows, and doors rattle. Feels like a heavy truck hitting walls.

Some people outdoors may feel movement. Parked cars rock. 4.3 - 4.8V Almost everyone feels movement. Sleeping people are

awakened. Doors swing open/close. Dishes break. Small objects move or are turned over. Trees shake. Liquids spill from open containers 4.9 - 5.4

VI Everyone feels movement. People have trouble walking. Objects fall from shelves. Pictures fall off walls. Furniture moves. Plaster in walls may crack. Trees and bushes shake. Damage slight in poorly built buildings. 5.5 - 6.1

VII People have difficulty standing. Drivers feel cars shaking. Furniture breaks. Loose bricks fall from buildings. Damage slight to moderate

in well-built buildings; considerable in poorly built buildings. 5.5 - 6.1VIII Houses not bolted down shift on foundations. Towers & chimneys fall.

Well-built buildings suffer slight damage. Poorly built structures severely damaged. Hillsides crack if ground is wet. Water levels in wells change. 6.2 - 6.9

IX Well-built buildings suffer considerable damage. Houses not bolted down move off foundations. Some underground pipes broken. Ground cracks. Serious damage to Reservoirs. 6.2 - 6.9

X Most buildings & their foundations destroyed. Some bridges destroyed. Dams damaged. Large landslides occur. Water thrown on the banks of canals, rivers, lakes. Ground cracks in large areas. Railroad tracks bent. 7.0 - 7.3

XI Most buildings collapse. Some bridges destroyed. Large cracks appear in the ground. Underground pipelines destroyed. Railroad tracks badly bent. 7.4 - 7.9

XII Almost everything is destroyed. Objects thrown into the air. Ground moves in waves or ripples. Large amounts of rock may move. >8.0

Table 3: Modified Mercalli scale intensity and its equivalent Richter scale magnitude

3.4 Seismic risk analysis and earthquake prediction 3.4.1 Long-term seismic prediction

A long-term prediction evaluates the potential for an earthquake of a certainmagnitude to occur and is usually expressed in probabilistic terms

For example, a USGS- study of 1999, suggests there is a 70% probability of anearthquake with a magnitude of 6.7 (or higher) hitting the San Francisco area, duringthe next 30 years

Methodology of long-term prediction:

1) Historical earthquake records and paleo-geological signals

2) Analysis of seismicity and seismic gaps in a certain zone

Progress towards long-term prediction during this time has been disappointing

3.4.1 Long-term seismic prediction (Loma Prieta, California)

3.4.2 Intermediate and short-term prediction

Intermediate-term prediction is based on identifying some type of precursoryphenomena which indicates that the actual occurrence of a real big earthquake isimminent. Precursory signals used for this purpose are the following

-- Patterns and intensity of foreshocks: These usually increase in magnitude andmay luster or migrate down a fault to where the main shock will eventually occur

-- Increase in ground deformation in the focal area (measured by GPS or interferometry) -- Rapid fluctuations in water levels in groundwater wells -- Dramatic increases in radon gases and electromagnetic radiation (Loma Prieta earthquake) -- Changes in P and, namely, S seismic wave velocities in the fault zone as an

indication of cracks that fill up with fluids (dilatancy model)

-- Anomalous animal behavior

4. Volcanoes4.1 Global distribution and characteristics

October 1980 eruption of Krafla Volcano. ===>

4. Volcanoes4.1 Characteristics

Volcanic eruptions are ejections of molten rock ("magma"), volcanic gas, and (or) pre-existing "country"rock onto the Earth's surface, driven by gas pressures in the magma or in ground water heated bymagma. Eruptions are either effusive (the magma pours out gently out of a vent) or explosive (magmaand overlying rock is ejected high in the air and fragmented into volcanic ash and larger blocks). Themixture of lava and solid debris and ash that flows down the flanks of a volcano is called the pyroclasticflow. Whether a volcano erupts explosively or effusively depends on several geological and petrologicalfactors, namely on the magma composition which determines also its temperature and its viscosity .

----------------------------------------------------------------------------------------------------------------------------volcanic rock silica (SiO2 ) content melting temperature (

oC) relative viscosity

Basalt (mafic) low (<50%) 1400 low Andesite intermediate (~60%) 1100 intermediate Rhyolite (felsic) high SiO2 (70-80%) 800 high---------------------------------------------------------------------------------------------------------------------------

Inverse relationship between the melting temperature of the magma source rock and its viscosity.

===> basaltic magma is more fluid than rhyolitic (Granite) magma. ===> volcanoes with rhyolitic magma kind will most likely erupt explosively, whereas basaltic volcanoes erupt effusively.

Other factor determining eruption is the volcanic gas content, mostly water vapour and CO2. To initiate aneruption, a certain gas pressure has to build up in the magma chamber. If this gas pressure builds fasterthan it is relieved, an eruption will be explosive; otherwise it will be effusive.

4.2 Volcanic Hazards

Primary effects (lava and ashes)

* Vesuvius (79 A.D. eruption, destroying Pompeii with 20,000 people perished

* 1902 Mont Pelée, Martinique eruption destroying St Pierre and killing 29000 people.

Secondary effects (mudflows, landslides, lahars) (often more desasttous)

Nevado del Ruiz, Colombia, volcano in 1985. Minor pyroclastic eruption caused melting oflarge amounts of snow and ice at the summit. 1-2 hours later cool lahars, further fluidizedby water from several days of rainfall, buried the town of Armero, killing 22,000 people.

Long-term tertiary climatic effects

(1) 1815, Tambora volcano, Indonesia, the largest eruption in recorded history. The year after (1816) was called the "year without summer". Snow fell in parts of Europe in July.

(2) 1981, El Chichón Volcano, Mexico, In this case, however, the effects were masked by a strong El Niño in the year after.

(3) 1991 Pinatubo, Philippines. A lowering of the average temperature by about 1 oC was observed for the two years after.

4.2 Volcanic Hazards (Mt. St. Helens, 1980, eruption)

4.3 Prediction of volcanic activity

Compared with earthquake prediction that of an impending volcanic eruption appears to have been moresuccessful, as well for the long- (10's of years) as for the intermediate-term range (months) . Short-termprediction (days, hours) has been possible for the 1982 eruption of the Mt. St. Helena and the Pinatubo,1991, eruption Unlike for earthquakes (where and when?) volcano prediction requires only the answer toquestion of when? the eruption will take place, allowing a more concentrated approach of monitoring thevolcano under question. Another helping factor is the larger number of geophysical and geologicalprecursory phenomena that are indicative of an imminent eruption. These include the following:

-- Seismic Activity: Volcanic eruptions are usually preceded by a sudden increase in the number ofearthquakes (seismic tremors) immediately below the volcano. Earthquakes occur also as magmamoves upward into the volcano.

-- Seismic exploration and monitoring - the position and movement of the magma body can be delineated by seismic tomography (e.g. Koch, 1985a,b; 1991; 1992a;b 1993a;b;c) using

seismic waves generated by both earthquakes and artificial explosions and recorded by arrays of seismographs placed around the volcano. Because S-wave will not travel through a liquid detectionan S-wave „shadow zone“ will be indicative of the location of the magma body.

-- Ground deformation - monitoring of changes in volcano topography induced by small dislocations in the volcano, possibly due to the magma movements -- Monitoring of volcanic gases - recognizing changes in gas chemistry and emission rates due to newly formed fissures or cracks -- Changes in thermal and magnetic properties of the volcano.

5 Landslides5.1 Causes

Landslides, called also massmovement in geology, areoften a secondary effect ofearthquakes or volcanoeruptions, though often theyare also primary disasterscaused after heavy rainfall orrapid snow melt, when waterinfiltrating into the groundreduces the stability of the soil, which, under gravitationalinfluence may start to movealong a downhill slope.

Safety Factor Fs = Shear Strength/Shear Stress

If Fs < 1.0, slope failure is expected.

5 Landslides5.1 Causes (soil mechanics)

Clay-rich soils are particularlyvulnerably, because of thetendency of clay to expand andloosing strength when soakedwith water.

Dry unconsolidated grains have a high frictional contact betweenthe grains

Under extreme conditions ofwater saturation liquefactionoccurs , and a „slurry“-likemudslide or lahar may develop that can rush in an avalanche-manner downhill.

5.2 Landslides: Occurrence and effects

5.2 Landslides: Occurrence and effects

Examples of disastrous regional landslide events are the

-- 1921 Kansu, China, landslide triggered by earthquake with 100,000 people killed.

-- 1966, Aberfan, UK, mine waste dump slope instability causing 144 deaths.

-- 1963, Vaiont reservoir (Italy) landslide which generated a flood wave that overtopped the dam anddrowned about 2,000 people.

-- 1970, Peru, debris avalanche also triggered by an earthquake buried the towns of Yungay andRanrahirca killing more than 18,000 people.

-- 1985, Nevado del Ruiz volcano, Colombia, triggered lahar.

Yungay, Peru's Main Plaza before(left) and after(right) pictures of landslide's destruction.

5.3 Prediction of landslides

Because the geologic and geotechnical conditions responsible for landsliding are generally wellunderstood, landslides also can be predicted with some success (IDNDR, 1999).

Long-term prediction relies on landslide hazard maps that are set up based on previousexperience where critical topographical slopes are likely in an area (mountain regions).

Intermediate-term prediction will try to assess when the critical slope-stability will be exceededafter heavy rainfall, for example, based on theories of material science and geotechnicallaboratory tests. Predicting unusually wet seasons from regional weather patterns, e.g., theusually wet winters associated with El Niño along the Pacific Coast of North and South America,may become useful for intermediate-term forecasting of landslides.

Short-term prediction is based on direct landslide monitoring and has been greatly aided by thedevelopment of telemetry or satellite transmitting systems. Precursors of landslide movementsuch as the appearance of cracks or dislocations of small amounts of soil can be used to predict the onset of slope failure.

6 Tsunamis6.1 Causes, occurrences and effects

Tsunami are seismic sea waves or "tidal" waves that are caused by sudden displacement ofsea floor or submarine landslides, usually triggered by earthquakes or underwater volcanic volcanic eruptions. As such Tsunamis are secondary effects of these two categories ofhazards. Tsunamis are mostly restricted to the Pacific Ocean.

Shoaling of wave in shallow water ~30 m wave speed c = /gd ~700 km/hr in open oceanwavelength ~ 500km

Desastrous tsunamis

-- 1883, Krakatoa, Indonesia volcano eruption with a 35 m tsunami killing 36,000 people -- 1815, Tambora, Indonesia, eruption-triggered tsunami with 50,000-90,000 deaths.

6.2 Early warning of tsunamis

Mitigating tsunami hazards has beenachieved through the development ofearly warning systems to give peopleliving on coastlines enough time(several hours) to reach highergrounds. For earthquake-generatedtsunamis there is an operationalwarning system for the Pacific Oceanlocated on the Hawaii Island. Basedon instantaneous determinations of thelocations of large, shallowearthquakes under water a tsunamiwatch is initiated, pendingconfirmation by tidal gauges thatmeasure wave heights. Based on thewave-speed in the ocean basin, arrivaltimes of a tsunami can be estimated foreach point in the Pacific Ocean andcorresponding warnings in terms ofmaps can be given

7. Conclusions

* Some general concepts of quantifying natural hazards and disasters in terms of risk they pose to humans and their infrastructure are discussed

* It is demonstrated that this task requires a careful separation of the notions of hazard assessment, vulnerability, risk assessment and hazard prediction.

* A detailed presentation of the geological hazards and disasters, namely earthquakes, volcanic eruptions, landslides and tsunamis and the scientific approaches to assess

their risks and to provide measures of hazard reduction, mainly through prediction andearly warning is provided.

* It is illustrated, however, that in spite of large scientific efforts in recent decades, progress in effective disaster mitigation is minor, particularly with regard to earthquakeprediction, least not for the reason of increasing population pressure in some of themost hazardous regions of the world.