ch05 earth processes and natural hazards

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Our focus in Part 2 turns to the majornatural hazards: an introduction tohazardous processes (Chapter 5), earth-quakes, including tsunamis (Chapter 6),

volcanic activity (Chapter 7), flooding (Chapter 8),landslides (Chapter 9), coastal processes, includinghurricanes (Chapter 10 ) , and impacts of asteroidsor comets (Chapter 11). The purpose is not toprovide extensive amounts of detailed informa-tion concerning these natural processes that wedefine as hazards but to focus on the basicsinvolved and the environmental concerns result-ing from interactions between people and natural

processes and hazards. The major principlespresented are: 1) Earth is a dynamic environment,and change resulting from natural processes is thenorm rather than an exception; 2) we must strive to

P A R T

T W O

Earth Processes and Natural Hazards

learn all we can about natural processes andhazards so that effects on human society may beminimized; and 3) human population increase andchanging land use are greatly increasing the threatof loss of life and property to natural hazards.Of particular importance is the recognition of loca-tions where hazardous processes are going tooccur and their natural or human-induced returnperiod (time between events). We will learn thatthe environmentally preferred adjustment tonatural hazards is environmental planning toavoid those locations where the hazards are mostlikely to occur and to zone the land appropriately.

Environmental planning involves detailed studyof natural processes and mapping of thoseprocesses to produce environmental maps usefulin the planning process.



F I V E



Learning Objectives

Natural hazards are naturally occurring pro-

cesses that may be dangerous to human life

and structures. Volcanic eruptions, earthquakes,

floods, and hurricanes are all examples of

natural hazards. Human population continues

to increase, and there is a need to develop

environmentally sound strategies to minimize

the loss of life and property damage from

hazards, especially in urban areas. The study of

hazardous processes, therefore, constitutes

one of the main activities of environmental geol-

ogy. The learning objectives for this chapter are

Understand why increasing population and

changing land use increase the threat of loss

of life and property from a natural disaster to

the level of a catastrophe

Know the conditions that make some natural

Earth processes hazardous to people

Understand how a natural process that gives

rise to disasters may also be beneficial to

people

Understand the various natural processes

that constitute hazards to people and property

Know why history, linkages between pro-

cesses, prediction, and risk assessment are

important in determining the threat from

natural hazards

Know how people perceive and adjust to

potential natural hazards

Know the stages of recovery following natural

disasters and catastrophes

133

Introduction to Natural Hazards

Hurricane Katrina, a giant storm Hurricane Katrina approach-

ing New Orleans region—aerial image. (NOAA)



134 Chapter 5 Introduction to Natural Hazards

Hurricane Katrina, Most Serious NaturalCatastrophe in U.S. History

Hurricane Katrina (see opening photograph) made landfall inthe early evening of August 29, 2005, about 45 km (30 miles)to the east of New Orleans. Katrina was a huge storm that

caused serious damage up to 160 km (100 mi) from its center.The storm produced a storm surge (a mound of water pushedonshore by the storm) of 3 to 6 meters (9 to 20 feet). Much of the coastline of Louisiana and Mississippi was devastated ascoastal barrier islands and beaches were eroded and homesdestroyed. Property damage from Hurricane Katrina andcosts to rehabilitate or rebuild the area may exceed $100 bil-lion, making it the most costly hurricane in the history of theUnited States. The number of human deaths will never beknown for sure, as many bodies may have been washed outto sea or buried too deep to be found. The official number of deaths is 1,836. The hurricane and subsequent flooding setinto motion a series of events that caused significant environ-mental consequences. Initial loss of life and property fromwind damage and storm surge was immense. Entire coastalcommunities disappeared with their fishing industry.

At first it was thought the city of New Orleans had beenspared, as the hurricane did not make a direct hit. The sit-uation turned into a catastrophe when water from LakePontchartrain, north of the city and connected to the Gulf,flooded the city. Levees capped with walls, constructed tokeep the water in the lake and protect low-lying parts of thecity, collapsed in two locations and water poured in. Anotherlevee failed on the Gulf side of the city and contributed tothe flooding. Approximately 80 percent of New Orleans wasunder water from knee deep to rooftop or greater depths(Figure 5.1). People who could have evacuated but didn’t,

and those who couldn’t because they lacked transportation,took the brunt of the storm. A part of the city that wasn’tflooded was in the French Quarter (Old Town), which is thearea of New Orleans famous for music and Mardi Gras. Thepeople who built New Orleans over two hundred years agorealized that much of the area was low in elevation and builton the natural levees of the Mississippi River. The naturallevees formed by periodic overbank deposition of sediment

from the river over thousands of years. They are parallel tothe river channel and are higher than the adjacent land,providing natural flood protection.

As marshes and swamps were drained in lower areas, thecity expanded into low areas with a much greater floodhazard. Much of the city is in a natural bowl and parts are ameter or so (3 to 9 feet) below sea level (Figure 5.2).

It has been known for a long time that if a large hurricanewere to make a direct or near-direct hit on the city, extensiveflooding and losses would result. The warnings were notcompletely ignored, but sufficient funds were not forthcom-ing to maintain the levee and system of floodwalls to protectlow-lying areas of the city from a large hurricane.

The fact that the region is subsiding at highly variablerates from 1 to 4 m (3 to 12 feet) per 100 years contributed tothe flood hazard. Over short periods, 50 percent to 75 percentof the subsidence in some areas is natural, resulting fromgeologic processes (movement along faults) that formed theGulf of Mexico and the Mississippi River delta.1 As much asseveral meters (more than 10 feet) of subsidence has occurredin the last 100 years, and during that period sea level has risenabout 20 cm (8 in.). The rise is due in part to global warming.As the Gulf water and ocean water warm, they expand, rais-ing sea level. The subsidence results in part from a number of human processes including extraction of groundwater, oil,and gas, as well as loss of freshwater wetlands that compactand sink when denied sediment from the Mississippi River.Because the Mississippi River has artificial levees (embank-ments constructed by humans), it no longer delivers sedimentto the wetlands. Therefore wetlands have stopped building

up from sediment accumulation. Before the levees wereconstructed in the Mississippi River delta, floodwater with itssediment spread across the delta helping maintain wetlandsoils and plants. The freshwater wetlands near New Orleanswere largely removed during past decades. As wetlands areremoved, they are replaced by saltwater ecosystems as sealevel rises and the land continues to subside. The freshwaterwetlands are a better buffer to winds and storm waves thanare saltwater wetlands. Tall trees such as cypress and otherplants of freshwater wetlands (Figure 5.3) provide roughnessthat slows down water from high waves or storm surgemoving inland. It’s well known that one of the natural servicefunctions of both saltwater and freshwater coastal wetlands isto provide protection to inland areas from storms.

New Orleans Will Be Rebuilt. The people of New Orleansare resilient and will move back into this famous historic city.We have learned from this event and better measures are beingtaken to ensure that this kind of catastrophe is less likely tooccur in the future. For example, in some areas where floodwaters, even with future levee failure, will be less than onestory high, reconstruction includes flood-proof buildings byconstructing living areas on the second floor.

The U.S. Army Corps of Engineers, which is largelyresponsible for the flood protection of New Orleans,produced a draft report in June 2006 concerning the hurricaneand flood protection system. They acknowledged that the

system had evolved piecemeal over a number of decades and

CASE HISTORY

Figure 5.1 Katrina floods New Orleans New Orleans was flooded when flood defenses failed during Hurricane Katrina. (N. Smiley/Pool/

Dallas Morning News/Corbis)



Introduction to Natural Hazards 135

A

B

Natural bowl(subsiding)

MississippiRiver

LakePontchartrain

Sea Level

FloodProtection~ 7m Flood

ProtectionLevel ~ 6m

NaturalLevee

Levee

DowntownNew OrleansOld Town —

Latin Quarter

DrainedMarsh & Swamp

Canal St.

Univ. New Orleans

Ear har t Expy

OX

udubon

Golf Club

Tulane University

Of Louisiana

Notre Dame

Seminary

lton Ochsner

Medical Foundation

City Park

Golf Course

New Orleans

University

Of New Orleans

Lake

Willow

New Orleans

Lakefront irport

Gretna

Our Lady

Of Holy Cross College

Gretna Our LadyOf Holy Cross College

Chalmette

National Historical Park

ChalmetteNational Historical Park

M i s s i s s i p

p i R i

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New OrleansLakefront Airport

LakeWillowUniversity

Of New Orleans

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City ParkGolf Course

Alton OchsnerMedical Foundation Notre Dame

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AudubonGolf Club

LakePontchartrain

N0 2 3 km

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A

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10

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Figure 5.2 Map and cross section of New Orleans Much of the city is below sea level betweenthe Mississippi River and Lake Pontchartrain. (Edward A. Keller)

that it was a system in name only. Nevertheless, the floodprotection structures were constructed to protect the city andtheir failure was responsible for a majority of the floodingthat resulted from Hurricane Katrina in 2005.

Some conclusions of the report2 are

There were no fallback redundancies (second-tier protec-

tion) to the flood protection if the primary flood control

structures failed. Pumping stations designed to removefloodwaters were the only example of a redundant systemand these were not designed to function in a majorhurricane with extensive flooding.

Hurricane Katrina exceed the design criteria of the floodprotection structures. Some levee and floodwall failures

resulted from being overtopped by floodwaters. Others




failed, without being overtopped, by erosion from theirfront side.

Regional subsidence has been faster than was appreciated.The heights of the flood protection structures were notadjusted for subsidence, and some of the floodwalls andlevees were as much as 1m (3 ft) below the elevation theywere designed at.

Although scientific knowledge about hurricanes andstorm surges has increased, this did not lead to updatingthe flood control plan. What adjustment did occur wasfragmented rather than consistent and uniform.

Consequences of flooding were also concentrated. Morethan 75 percent of the people who died were over 60 yearsold and were located in areas with greatest depth of flood-ing. The larger number of deaths of the elderly occurred because poor, elderly people and disabled people were theleast able to evacuate without assistance.

Parts of the flood and hurricane protection system have been repaired at a cost of about $800 million since Katrina,and these are the strongest parts of the flood protection. At

present, the protection level remains the same as beforeKatrina.

In fairness to the Corps, flood control structures are oftenunderfunded, and as with New Orleans, construction is

Figure 5.3 Cypress tree

freshwater wetlands along the coastof Louisiana. (Tim Fitzharris/Minden

Pictures)

spread over many years. Hopefully, we have learned fromKatrina and will build a stronger, more effective hurricaneprotection system for the city of New Orleans, as well as otherU.S. cities where hurricanes are likely to occur.

An important question is, can flooding occur again evenif higher, stronger flood defenses are constructed? Of course itcan—when a bigger storm strikes, future damage is in-

evitable. If freshwater marshes are restored and the riverwaters of the Mississippi allowed to flow through them again,they will help provide a buffer from winds and waves. Aspreviously mentioned, freshwater marshes have trees thatprovide a roughness to the land that slows wind and retardsthe advance of waves from the gulf. Every 1.5 km (1 mile) of marsh land can reduce waves by about 25 cm (1 ft).

Tremendous amounts of money will need to be spent tomake New Orleans more resistant to future storms. In light of the many billions of dollars in damages from catastrophes, itseems prudent to spend the money in a proactive way toprotect important resources, particularly in our major cities.

In the remainder of this chapter, we will discuss some of the principles of natural processes we know as hazards

and how they produce disasters and catastrophes. You willlearn how poor land uses and changing land uses, coupledwith population increase, greatly increase the risk of somehazards.

5.1 Hazards, Disasters, and Natural Processes

Natural Disasters: Loss of Life and Property DamagesNatural disasters, which are events that cause great loss of life or property damage,or both, such as earthquakes, floods, cyclones (hurricanes), have in the past fewdecades killed several million people, with an average worldwide annual loss of life of about 150,000 people. The financial losses resulting from natural disastersnow exceed $50 billion per year and do not include social impacts such as loss of employment, mental anguish, and reduced productivity. Three individual disas-ters, a cyclone accompanied by flooding in Bangladesh in 1970, an earthquake in

China in 1976, and a tsunami in the Indian Ocean in 2004, each claimedover 250,000



Hazards, Disasters, and Natural Processes 137

(a) (b)

Figure 5.4 Dams and beaches (a) Sediment from the Ventura River in southern California isdelivering some sand to beaches in the region; however, an old upstream dam (b) is storing sand thatmight otherwise nourish the beach. The dam is scheduled to be removed. ([a] Pacific Western;

[b] Edward A. Keller)

lives. These terrible disasters (catastrophes) were caused by natural hazards thathave always existed—atmospheric disturbance and tectonic movement—but theirextent was affected by human population density and land-use patterns.

Why Natural Processes Are Sometimes HazardsNatural hazards are basically natural processes. These processes become

hazardous when people live or work in areas where they occur. Natural processescan also become hazards when land-use changes, such as urbanization ordeforestation, affect natural processes, causing flooding or landsliding. It is theenvironmental geologist’s role to identify potentially hazardous processes andmake this information available to planners and decision makers so that they canformulate various alternatives to avoid or minimize the threat to human life orproperty. However, the naturalness of hazards is a philosophical barrier that weencounter whenever we try to minimize their adverse effects. For example, we tryto educate people that a river and floodplains, the flat land adjacent to the river,are part of the same natural system and that we should expect floods on flood-plains as the name suggests. Minimizing the flood hazard may be as simple as not

building on floodplains! However, this seemingly logical solution is difficult to get

across to people who see floodplains as flat land on which to build houses.

Magnitude and FrequencyThe impact of a disastrous event is in part a function of its magnitude, or amount of energy released, and frequency, or recurrence interval; however, it is influenced bymany other factors, including climate, geology, vegetation, population, and landuse. In general, the frequency of such an event is inversely related to the magni-tude. Small earthquakes, for example, occur more often than do large ones (see ACloser Look: The Magnitude-Frequency Concept).

Benefits of Natural Hazards

It is ironic that the same natural events that take human life and destroy propertyalso provide us with important benefits or natural service functions. For example,periodic flooding of the Mississippi River supplies nutrients to the floodplain, onwhich form the fertile soils used for farming. Flooding, which causes erosion onmountain slopes, also delivers river sediment to beaches (Figure 5.4) and flushes



pollutants from estuaries in the coastal environment. Landslides may bring benefits to people when landslide debris forms dams, creating lakes in mountain-ous areas (Figure 5.5). Although some landslide-created dams will collapse andcause hazardous downstream flooding, dams that remain stable can providevaluable water storage and are an important aesthetic resource.

Volcanic eruptions have the potential to produce catastrophes; however, they

also provide us with numerous benefits. They often create new land, as in the caseof the Hawaiian Islands, which are completely volcanic in origin (Figure 5.6).Nutrient-rich volcanic ash may settle on existing soils and quickly becomeincorporated, creating soil suitable for wild plants and crops. Earthquakes canalso provide us with valuable services. When rocks are pulverized during anearthquake, they may form an impervious clay zone known as a fault gougealong the fault. In many places, fault gouge has formed groundwater barriersupslope from a fault, producing natural subsurface dams and water resources.Along some parts of the San Andreas fault in the arid Coachella Valley near Indio,California, this process has produced oases, in which pools of water are surround-ed by native palm trees in an otherwise desert environment (Figure 5.7). Inaddition, earthquakes are also important in mountain building and thus are

directly responsible for many of the scenic resources of the western United States.


The Magnitude-Frequency Concept

The magnitude-frequency concept states that there is gener-ally an inverse relationship between the magnitude of anevent and its frequency. For example, the larger the flood, theless frequently such a flood occurs. The concept also includesthe idea that much of the work of forming Earth’s surfaceoccurs through events of moderate magnitude and frequencyrather than by common natural processes of low magnitudeand high frequency or by extreme events of high magnitudeand low frequency.

As an analogy to the magnitude-frequency concept, con-sider the work of reducing the extent of a forest by residenttermites, human loggers, and elephants (Figure 5.A). Thetermites are numerous and work quite steadily, but they are so

small that they can never do enough work to destroy all thetrees. The people are fewer and work less often, but, beingstronger than termites, they can accomplish more work in agiven time. Unlike the termites, the people can eventually fellmost of thetrees. Theelephants arestronger still andcanknockdownmanytreesinashorttime,butthereareonlyafewofthemand they rarely visit the forest. In the long run the elephants doless work than thepeople andbringabout less change.

In our analogy it is humans who, with a moderate expen-diture of energy and time, do the most work and change theforest most drastically. Similarly, natural events with mod-erate energy expenditure and moderate frequency are oftenthe most important shapers of the landscape. For example,

Figure 5.A Human scale of

change Human beings with our high

technology are able to down even thelargest trees in our old-growth forests.The lumberjack shown here is working in a national forest in the PacificNorthwest. (William Campbell/

Sygma Photo News)

A CLOSER LOOK




LakeDam

Figure 5.5 Landslide dam

Landslide dam forming a lake in Utah.

(Michael Collier)

Ocean

Ocean

Beach Wavefront

Wavefront

Salt marsh

Salt marsh

Newsand spit

New inlet(tidal flow)

(a) Before hurricane

(b) After hurricane

•New inlet and sand spit •Dune vegetation denuded •Frontal dunes eroded •Salt marsh vegetation eroded

Frontal sanddune line

Barrier island,sand

0

1 K m

Salt marshvegetation

Movement of sedimentand water

Small trees onback dune areas

Figure 5.B Hurricanes change coasts Idealized diagram showing the formation of an inletthrough a barrier island resulting from erosion during a hurricane. (a) Before and (b) after hurricane.

most of the sediment carried by rivers in regions within asubhumid climate (most of the eastern United States) is trans-ported by flows of moderate magnitude and frequency.However, there are many exceptions. In arid regions, forexample, much of the sediment in normally dry channels

may be transported by rare high-magnitude flows produced by intense but infrequent rainstorms. Along the barrier-islandcoasts of the eastern United States, high-magnitude stormsoften cut inlets that cause major changes in the pattern andflow of sediment (Figure 5.B).




(a) (b)

Figure 5.7 Oases and faults (a) Native palm trees along the San Andreas fault, Coachella Valley,California.The fault dams groundwater that the trees use. (b) In some cases the water forms surface pools

and an oasis. (Edward A. Keller)

Death and Damage Caused by Natural HazardsWhen we compare the effects of various natural hazards, we find that those thatcause the greatest loss of human life are not necessarily the same as thosethat cause the most extensive property damage. Table 5.1 summarizes selectedinformation about the effects of natural hazards in the United States. The largestnumber of deaths each year is associated with tornadoes (Figure 5.8) and wind-storms, although lightning (Figure 5.9), floods, and hurricanes also take a heavytoll. Loss of life due to earthquakes can vary considerably from one year to thenext, as a single great quake can cause tremendous human loss. It is estimated thata large, damaging earthquake in a densely populated part of California couldinflict $100 billion in damages while killing several thousand people.3 The 1994

Northridge earthquake in the Los Angeles area killed approximately 60 peopleand caused more than $30 billion in property damage. In fact, property damagefrom individual hazards is considerable. Floods, landslides, frost, and expansivesoils each cause mean annual damages in the United States in excess of $1.5 billion.Surprisingly, expansive soils, clay-rich soils that expand and contract with wettingand drying, are one of the most costly hazards, causing over $3 billion in damages

(a) (b)

Figure 5.6 New land from volcanic eruption New land being added to the island of Hawaii. (a) Theplume of smoke in the central part of the photograph is where hot lava is entering the sea. (b) Closeup of an advancing lava front near the smoke plume. (Edward A. Keller)




TABLE 5.1 Effects of Selected Hazards in the United States

No. of Occurrence

Deaths Influenced by Catastrophe

Hazard per Year Human Use Potential2

Flood 86 Yes H

Earthquake1 Yes H

Landslide 25 Yes M

Volcano1 No H

Coastal erosion 0 Yes L

Expansive soils 0 No L

Hurricane 55 Perhaps H

Tornado and windstorm 218 Perhaps H

Lightning 120 Perhaps L

Drought 0 Perhaps M

Frost and freeze 0 Yes L

1Estimate based on recent or predicted loss over 150-year period. Actual loss of life and/or property

could be much greater.

2Catastrophe potential: high (H), medium (M), low (L).

Source: Modified after White, G. F., and Haas, J. E. 1975. Assessment of research on natural hazards.

Cambridge, MA: MIT Press.

<1

50 ?

annually to building foundations, sidewalks (Figure 5.10), driveways, andswimming pools.

An important aspect of all natural hazards is their potential to produce acatastrophe. A catastrophe is any situation in which the damages to people,property, or society in general are sufficient such that recovery or rehabilitation is a

(a) (b)

Figure 5.8 Tornado hazard (a) Tornado in Tampa Bay, Florida, on July 12, 1995. (Brian Baer/

St. Petersburg Times/AP/Wide World Photos) (b) Mobile homes destroyed by tornado that struck

Benton, Louisiana, on April 4, 1999. (Eric Gay/AP/Wide World Photos)




Figure 5.10 Soil hazard

Organic-rich expansive soils are crack-ing the walls of this building in Spain.

(Edward A. Keller)

Figure 5.9 Lightning strike Lightning is responsible for more than 100 deaths each year in the UnitedStates. Shown here are lightning strikes near Walton, Nebraska. (Joel Sartore/NGS Image Collection)

long, involved process.4 Table 5.1 shows the catastrophe potential for the hazardsconsidered. The events most likely to produce a catastrophe are floods, hurricanes,tornadoes, earthquakes, volcanic eruptions, and large wildfires (not included inTable 5.1). Landslides, which generally cover a smaller area, have only a moderatecatastrophe potential. The catastrophe potential of drought is also moderate:though a drought may cover a wide area with high financial losses, there is usuallyplenty of warning time before its worst effects are experienced. Hazards with a lowcatastrophe potential include coastal erosion, frost, lightning, and expansive soils.

The effects of natural hazards change with time. Changes in land-use patternsthat influence people to develop on marginal lands, urbanization that changes thephysical properties of Earth materials, and increasing population all alter theeffects of natural hazards. Although damage from most hazards in the UnitedStates is increasing, the number of deaths from many hazards is decreasing

because of better hazard forecasting and warning to the public.



Evaluating Hazards: History, Linkages, Disaster Prediction, and Risk Assessment 143

5.2 Evaluating Hazards: History, Linkages, Disaster

Prediction, and Risk Assessment

Fundamental Principles Concerning Natural HazardsThe understanding of natural hazards and how we might minimize their impact onpeople and the environment is facilitated through the recognition of five principles:

1. Hazards are known from scientific evaluation. Natural hazards, such as earth-quakes, volcanic eruptions, landslides, and floods, are natural processesthat can be identified and studied using the scientific method. Most hazardousevents and processes can be monitored and mapped, and their future activ-ity can be evaluated based on the frequency of past events, patterns, and typesof precursor events.

2. Risk analysis is an important component in understanding impacts resulting from hazardous processes. Hazardous processes are amenable to risk analy-sis based on the probability of an event occurring and the consequencesresulting from that event; for example, if we were to estimate that in anygiven year in Los Angeles or Seattle there is a 5 percent chance of a moder-

ate earthquake occurring. If we know the consequence of that earthquake interms of loss of life and damage, then we can calculate the risk to society of that earthquake actually happening.

3. Hazards are linked. Hazardous processes are linked in many ways, from sim-ple to complex. For example, earthquakes can produce landslides and giantsea waves called tsunamis, and hurricanes often cause flooding and erosion.

4. Hazardous events that previously produced disasters are often now produc-ing catastrophes. The size of the natural hazardous event as well as itsfrequency is influenced by human activity. As a result of increasing humanpopulation and poor land-use practices, what used to be disasters are oftennow catastrophes.

5. Consequences of hazards can be minimized. Minimizing the potential adverse

consequences and effects of natural hazards requires an integrated approachthat includes: scientific understanding; land-use planning (regulation andengineering); and proactive disaster preparedness.

Role of History in Understanding HazardsA fundamental principle of understanding natural hazards is that they arerepetitive events, and therefore studying their history provides much neededinformation in any hazard reduction plan. Whether we are studying flood events,landslides, volcanic eruptions, or earthquakes, the historical and recent geologichistory of an area is a primary data set. For example, if we wish to evaluate theflooding history of a particular river, one of the first tasks is to study the previousfloods of that river system. This study should include detailed evaluation of aerial

photographs and maps reaching as far back as the record allows. For prehistoricevents, we can study the geologic environment for evidence of past floods, such asthe sequence of flood deposits on a floodplain. Often, these contain organic mate-rial that may be dated to provide a history of prehistoric flood events. This historyis then linked with the documented historical record of high flows, providing aperspective on flooding of the river system being evaluated. Similarly, if we areinvestigating landslides in a particular river valley, studying the documentedhistorical occurrence of these events and linking that information to prehistoriclandslides will provide basic data necessary to better predict landslides.

The hydrologists’ role in flood analysis is to evaluate stream flow records takenfrom sites, known as gauging stations, where stream flow recorders have beenestablished (Figure 5.11). Unfortunately, except for larger rivers, the records are

usually relatively short, covering only a few years. Most small streams have no




gauging station at all. Geologists have the observation skills, tools, and training to“read the landscape.” They can evaluate prehistoric evidence for natural hazardsand link this information with the modern record to provide the perspective of time on a particular process. Environmental geologists also have the ability torecognize landforms associated with hazardous processes. In addition, they recog-nize that the nature and extent of the hazard varies as the assemblage of landformsvaries. For example, flooding that occurs in a river valley with a flat adjacentfloodplain is very different from flooding on a delta. The river and floodplain

constitute a relatively simple system consisting of a single channel bordered by thefloodplain (Figure 5.12). Deltas, however, are more complex landforms, producedwhen a river enters a lake or an ocean (Figure 5.13). Deltas often have multiplechannels that receive floodwaters at various times and places, varying the position

Figure 5.11 Monitoring

stream flow Stream gauging station on the Merced River in Yosemite National Park continu-ously monitors the flow of waterin the river. Solar cells providepower.This is not a “run of themill”station. It is designed to

educate park visitors on how stream flow is recorded.(Edward A. Keller)

Figure 5.12 Floodplain

Mission Creek, California (left), andfloodplain (right) with an urbanpark on it.The location of the park

is an example of good use of afloodplain. (Edward A. Keller)




of the channel and thus the energy of a flood. Processes on deltas are discussed indetail in Chapter 8, but the general principle of instability of channels associatedwith different types of landforms is the idea we wish to emphasize here.

In summary, before we can truly understand the nature and extent of a naturalhazard, for example, flooding at a particular site, we must study in detail thehistory of the site, especially the occurrence, location, and effects of past floods.Understanding this history provides a perspective on the hazard that allows forthe “big picture” to be better understood and appreciated. Integrating historicalinformation with both present conditions and land-use change of the recent past,such as deforestation and urbanization, allows for better understanding of the

hazard. This results because land-use changes can increase the impact of hazardssuch as landslides and floods. Studying the record also enables more reliableprediction of future events.

Linkages between Hazardous EventsLinkages between natural processes that are hazardous to people generally fallinto two categories. First, many of the hazards themselves are linked. For exam-ple, hurricanes are often associated with flooding, and intense precipitationassociated with hurricanes causes coastal erosion and landslides on inland slopes.Natural hazards and the characteristics of Earth materials provide a second typeof linkage. For example, the sedimentary rock known as shale is composed of loosely cemented or compacted tiny sediments that are prone to landslides.

Granite provides another example of the linkage between natural hazards andEarth material characteristics. Although generally strong and durable, granite isprone to sliding along fractures within the rock.

Disaster Forecast, Prediction, and WarningA prediction of a hazardous event such as an earthquake involves specifying thedate, time, and size of the event. This is different from predicting where or howoften a particular event such as a flood will occur. A forecast, on the other hand,has ranges of certainty. The weather forecast for tomorrow may state there is a40 percent chance of showers. Learning how to predict or forecast disasters inorder to minimize loss of life and property damage is an important endeavor. Foreach particular hazard, we have a certain amount of information; in some cases,

this information allows us to predict or forecast events accurately. When insuffi-cient information is available, the best we can do is to locate areas where disastrous

Mediterranean Sea

Nile Delta

Egypt

N i l e

R i v e

r

Figure 5.13 Delta Infraredimage of the Nile Delta (upper left)and surrounding region. Healthy vegetation is red. The white strips atthe delta edge are sandy islands thathave a serious erosion problem sincethe construction of the Aswan Dam(not shown) in 1964. (Earth Satellite

Corporation/SPL/Photo Researchers, Inc.)




events have occurred and infer where and when similar future events might takeplace. If we know both the probability and the possible consequences of an event’soccurring at a particular location, we can assess the risk the event poses to peopleand property, even if we cannot accurately predict when it will occur.

The effects of a specific disaster can be reduced if we can forecast or predictthe event and issue a warning. In a given situation, most or all of the followingelements are involved:

Identifying the location where a hazardous event will likely occur

Determining the probability that an event of a given magnitude will occur

Observing precursor events

Forecasting or predicting the event

Warning the public

Location. For the most part, we know where a particular kind of event is likely tooccur. On a global scale, the major zones for earthquakes and volcanic eruptionshave been delineated by mapping earthquake foci and the locations of recentvolcanic rocks and volcanoes. On a regional scale, we can predict from pasteruptions which areas in the vicinity of certain volcanoes are most likely to be

threatened by large mudflows or ash in the event of future eruptions. This risk has been delineated for most large volcanoes, including the Pacific Northwest’sCascade Range and volcanoes in Alaska, Japan, Italy, Mexico, Central and SouthAmerica, Hawaii, and numerous other volcanic islands in the oceans of the world.On a local scale, detailed work with soils, rocks, and hydrology may identifyslopes that are likely to fail and cause a landslide or where expansive soils exist.Certainly we can predict where flooding is likely to occur from the location of thefloodplain and evidence from recent floods such as the location of flood debrisand high-water line.

Probability of Occurrence. Determining the probability that a particular eventwill occur in a particular location within a particular time span is an essential goalof hazard evaluation. For many large rivers we have sufficient records of flow to

develop probability models that can reasonably predict the average number of floods of a given magnitude that will occur in a given time period. Likewise,droughts may be assigned a probability on the basis of past occurrence of rainfallin the region. However, these probabilities are similar to the chances of throwing aparticular number on a die or drawing an inside straight in poker; the element of chance is always present. For example, the 10 year flood may occur on the averageof every 10 years, but it is possible for several floods of this magnitude to occur inany one year, just as it is possible to throw two straight sixes with a die.

Precursor Events. Many hazardous events are preceded by precursor events. Forexample, the surface of the ground may creep, or move slowly down a slope,for a period of time, days to months, before a landslide. Often the rate of creep

increases up to when the landslide occurs. Volcanoes sometimes swell or bulge before an eruption, and often emissions of volcanic gases accompanied by seismicactivity significantly increase in local areas surrounding the volcano. Foreshocksand anomalous, or unusual, uplift may precede earthquakes. Precursor eventshelp predict when and where an event is likely to happen. For example, landslidecreep or swelling of a volcano may result in the issuance of a warning, allowingpeople to evacuate a hazardous area.

Forecast. When a forecast of an event is issued, the certainty of the event is given,usually as the percent chance of something happening. When we hear a forecast of a hazardous event, it means we should be prepared for the event.

Prediction. It is sometimes possible to accurately predict when certain natural

events will occur. Flooding of the Mississippi River, which occurs in the spring in




response to snowmelt or very large regional storm systems, is fairly common, andwe can often predict when the river will reach a particular flood stage, or waterlevel. When hurricanes are spotted far out to sea and tracked toward the shore, wecan predict when and where they will likely strike land. Tsunamis, or seismic seawaves, generated by disturbance of ocean waters by earthquakes or submarinevolcanoes, may also be predicted. The tsunami warning system has been fairlysuccessful in the Pacific Basin and can predict the arrival of the waves. A shorttime prediction of a hazardous event such as a hurricane motivates us to act nowto reduce potential consequences before the event happens.

Warning. After a hazardous event has been predicted or a forecast has been made,the public must be warned. Information leading to the warning of a possible disas-

ter such as a large earthquake or flood should move along a path similar to thatshown in Figure 5.14. The public does not always welcome such warnings,however, especially when the predicted event does not come to pass. In 1982, whengeologists advised that a volcanic eruption near Mammoth Lakes, California, wasquite likely, the advisory caused a loss of tourist business and apprehension on thepart of the residents. The eruption did not occur, and the advisory was eventuallylifted. In July 1986, a series of earthquakes occurred over a 4 day period in thevicinity of Bishop, California, in the eastern Sierra Nevada. The initial earthquakewas relatively small and was felt only locally; but a later, larger earthquake causingsome damage also occurred. Investigators concluded there was a high probabilityan even larger quake would occur in the same area in the near future and issued awarning. Local business owners, who feared the loss of summer tourism, felt thatthe warning was irresponsible; in fact, the predicted quake never materialized.

Incidents of this kind have led some people to conclude that scientific predic-tions are worthless and that advisory warnings should not be issued. Part of theproblem is poor communication between the investigating scientists and reportersfor the media (see A Closer Look: Scientists, Hazards, and the Media). Newspaper,television, and radio reports may fail to explain the evidence or the probabilisticnature of disaster prediction. This failure leads the public to expect completelyaccurate statements as to what will happen. Although scientific predictions of volcanic eruptions and earthquakes are not always accurate, scientists have aresponsibility to publicize their informed judgments. An informed public is betterable to act responsibly than an uninformed public, even if the subject makes peopleuncomfortable. Ship captains, who depend on weather advisories and warningsof changing conditions, do not suggest that they would be better off not knowing

about an impending storm, even though the storm might veer and miss the ship.

WARNING

Scientists

PUBLIC

Local officialsRegionalofficials

PRE

DICTI

ON

Predictionreviewgroup

DATA

Figure 5.14 Hazard prediction

or warning Possible flow path forissuance of a natural disasterprediction or warning.




Scientists, Hazards, and the Media

People today learn what is happening in the world by watch-ing television, listening to the radio, surfing the Internet, orreading newspapers and magazines. Reporters for the mediaare generally more interested in the impact of a particularevent on people than in its scientific aspects. Even majorvolcanic eruptions or earthquakes in unpopulated areas mayreceive little media attention, whereas moderate or even smallevents in populated areas are reported in great detail. Thenews media want to sell stories, and spectacular events thataffect people and property “sell.”5

Establishing good relations between scientists and thenews media is a goal that may be difficult to always achieve.In general, scientists tend to be conservative, critical peoplewho are afraid of being misquoted. They may perceivereporters as pushy and aggressive or as willing to presenthalf-truths while emphasizing differences in scientific opin-ion to embellish a story. Reporters, on the other hand, may

perceive scientists as an uncooperative and aloof group whospeak in an impenetrable jargon and are unappreciative of thedeadlines that reporters face.5 These statements about scien-tists and media reporters are obviously stereotypic. In fact,

both groups have high ethical and professional standards;nevertheless, communication problems and conflicts of inter-est often occur, affecting the objectivity of both groups.

Because scientists have an obligation to provide the publicwith information about natural hazards, it is good policy for aresearch team to pick one spokesperson to interact with themedia to ensure that information is presented as consistentlyas possible. Suppose, for example, that scientists are studyinga swarm of earthquakes near Los Angeles and speculationexists among them regarding the significance of the swarm.Standard operating procedure for Earth scientists working ona problem is to develop several working hypotheses andfuture scenarios. However, when scientists are working withthe news media on a topic that concerns people’s lives andproperty, their reports should be conservative evaluationsof the evidence at hand, presented with as little jargon aspossible. Reporters, for their part, should strive to provide

their readers, viewers, or listeners with accurate informationthat the scientists have verified. Embarrassing scientists bymisquoting them will only lead to mistrust and poor commu-nication between scientists and journalists.

A CLOSER LOOK

Just as weather warnings have proved very useful for planning ships’ routes,official warnings of hazards such as earthquakes, landslides, and floods are alsouseful to people making decisions about where they live, work, and travel.

Consider once more the prediction of a volcanic eruption in the Mammoth Lakesarea of California. The seismic data suggested to scientists that molten rock wasmoving toward the surface. In view of the high probability that the volcano would

erupt and the possible loss of life if it did, it would have been irresponsible forscientists not to issue an advisory. Although the eruption did not occur, the warningled to the development of evacuation routes and consideration of disaster pre-paredness. This planning may prove useful in the future; it is likely that a volcaniceruption will occur in the Mammoth Lakes area in the future. The most recent eventoccurred only 600 years ago! In the end, the result of the prediction is a betterinformed community that is better able to deal with an eruption when it does occur.

Risk AssessmentBefore discussing and considering adjustments to hazards,peoplemust have a goodidea of the risk that they face under various scenarios. Risk assessment is a rapidlygrowing field in the analysis of hazards, and its use should probably be expanded.

Risk Determination. The risk of a particular event is defined as the product of the probability of that event’s occurring multiplied by the consequences should itactually occur.6 Consequences, such as damages to people, property, economicactivity, and public service, may be expressed in a variety of scales. If, for example,we are considering the risk from earthquake damage to a nuclear reactor, we mayevaluate the consequences in terms of radiation released, which can further betranslated into damage to people and other living things. In any such assessment,it is important to calculate the risks of various possible events—in this example,earthquakes of various magnitudes. A large earthquake has a lower probability of occurring than does a small one, but its consequences are likely to be greater.

Acceptable Risk. Determining acceptable risk is more complicated. The risk that

an individual is willing to endure is dependent upon the situation. Driving anautomobile is fairly risky, but most of us accept that risk as part of living in a



modern world. However, acceptable risk from a nuclear power plant is very low because we consider almost any risk of radiation poisoning unacceptable. Nuclearpower plants are controversial because many people perceive them as high-riskfacilities. Even though the probability of a nuclear accident due to a geologichazard such as an earthquake may be quite low, the associated consequencescould be high, resulting in a relatively high risk.

Institutions, such as the government and banks, approach the topic of accept-

able risk from an economic point of view rather than a personal perception of therisk. For example, a bank will consider how much risk they can tolerate withrespect to flooding. The federal government may require that any property thatreceives a loan from them not have a flood hazard that exceeds 1 percent per year,that is, protection up to and including the 100 year flood.

Problems and Opportunities for Risk Assessment. A frequent problem of riskanalysis, with the exception of flooding on a river with a long record of past floods,is lack of reliable data available for analyzing the probability of an event. It can bedifficult to assign probabilities to geologic events such as earthquakes and volcaniceruptions, because the known chronology of past events is often inadequate.6 Simi-larly, it may be very difficult to determine the consequences of an event or series of events. For example, if we are concerned about the consequences of releasing radia-tion into the environment, localbiological,geologic, hydrologic, and meteorologicalinformation must be gathered to evaluate the radiation’s effects. This informationmay be complex and difficult to analyze. Despite these limitations, methods of determining the probability of earthquakes and volcanic eruptions are improving,as is ourability to estimate consequencesof hazardous events. Certainly, risk assess-ment is a step in the right direction and should be expanded. As more is learnedabout determining the probability and consequences of a hazardous event, we will

be able to provide more reliable forecasts and predictions necessary for decisionmaking, such as when to issue a warning or evacuate people from harm’s way.

5.3 The Human Response to Hazards

Often, the manner in which we deal with hazards is primarily reactive. After adisaster we engage in searching for and rescuing survivors, firefighting, andproviding emergency food, water, and shelter. There is no denying that theseactivities reduce loss of life and property and need to be continued. However, themove to a higher level of hazard reduction will require increased efforts toanticipate disasters and their impact. Land-use planning to avoid hazardouslocations, hazard-resistant construction, and hazard modification or control suchas flood control channels are some of the adjustments that anticipate future disas-trous events and may reduce our vulnerability to them.4

Reactive Response: Impact of and Recovery from Disasters

The impact of a disaster upon a population may be either direct or indirect. Directeffects include people killed, injured, displaced, or otherwise damaged by a partic-ular event. Indirect effects generally include responses to the disaster such asemotional distress, donation of money or goods, and paying taxes to finance therecovery. Direct effects are felt only by those individuals immediately affected bythe disaster, whereas indirect effects are felt by the populace in general.7,8

The stages of recovery following a disaster are emergency work, restoration of services and communication lines, and reconstruction. Figure 5.15 shows an ideal-ized model of recovery. This model can be applied to actual recovery activitiesfollowing events such as the 1994 Northridge earthquake in the Los Angeles area.Restoration began almost immediately after the earthquake. For example, in thefirst few weeks and months after the earthquake, roads were repaired and utilities

were restored with the help of an influx of dollars from federal programs, insurancecompanies, and other sources. The damaged areas in Northridge moved quickly

The Human Response to Hazards 149




from the restoration phase to the reconstruction I stage. We are now well into thereconstruction II period following the Northridge earthquake, and it is important toremember lessons from two previous disasters: the 1964 earthquake that struckAnchorage, Alaska, and the flash flood that devastated Rapid City, South Dakota, in1972. Anchorage began restoration approximately one month after the earthquakeas money from federal programs, insurance companies, and other sources poured

in. As a result, reconstruction was a hectic process, because everyone tried to obtainas much of the available funds as possible. In Rapid City, however, the restorationdidnotpeak until approximately10 weeks after theflood.The communitytook timeto carefullythink through thebest alternativesto avoid future flooding problems. Asa result, Rapid City today has an entirely different land use on the floodplain. Thefloodplain is now a greenbelt, with golf courses and other such activities, which hasgreatly reduced the flood hazard in the area (Figure 5.16). Conversely, the rapidrestoration and reconstruction in Anchorage were accompanied by little land-useplanning. Apartments and other buildings were hurriedly constructed across areasthat had suffered ground rupture and had simply been filled in and regraded. Byignoring the potential benefits of careful land-use planning, Anchorage is vulnera-

ble to the same type of earthquake damage that it suffered in 1964.4,7,8

In Northridge, the effects of the earthquake on highway overpasses and bridges, buildings, and other structures have been carefully evaluated to deter-mine how improved engineering standards for construction of new structures orstrengthening of older structures might be implemented during the reconstructionII period (Figure 5.15). Future earthquakes of moderate to large intensity arecertain to occur again in the Los Angeles area. Therefore, we must continue effortsin the area of earthquake hazard reduction.

Anticipatory Response: Perceiving, Avoiding,and Adjusting to HazardsThe options we choose, individually or as a society, for avoiding or minimizing theimpacts of disasters depend in part on our hazard perception.A good deal of work

has been done in recent years to try to understand how people perceive variousnatural hazards. This work is important because the success of hazard reduction

Periods Emergency Restoration

Restoration of major urban services

Return of refugees

Rubble cleared

Reconstruction I Reconstruction II

Capitalstock

Damaged ordestroyed

Patched Rebuilt(replacement)

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Normalactivities

Maximal

C o p

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a c

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.5 1 2 3 4 5 10 20 3040 100 200 300 400 500

Time (in weeks following disaster)

Completion of searchand rescue

Attain predisasterlevel of capitalstock and

activities

Completionof majorconstruction

projects

Ceased orchanged

Return andfunction

Return atpredisaster levels

or greater

Improved anddeveloped

End of emergencyshelter or feeding

Clearing rubblefrom main arteries

Figure 5.15 Recovery from

disaster Generalized model of recovery following a disaster. Thefirst 2 weeks after a disaster arespent in a state of emergency, in which normal activities are ceasedor changed. During the following 19 weeks, in the restoration

phase, normal activities returnand function, although perhapsnot at predisaster level. During the reconstruction I phase, foralmost 4 years after a disaster, thearea is being rebuilt and normalactivities return to predisasterlevels. Finally, during reconstruc-tion II, major construction anddevelopment are being done, andnormal activities are improvedand developed. (From Kates,

R.W., and Pijawka, D. 1977.

Reconstruction following disaster. In

From rubble to monument: The pace

of reconstruction, ed. J. E. Haas,R.W. Kates, and M. J. Bowden.

Cambridge, MA: MIT Press)



The Human Response to Hazards 151

programs dependson the attitudesof the people likely to be affected by the hazard.Although there is informed perception and understanding of a hazard at theinstitutional level among government agencies such as the U.S. Geological Surveyand state or local flood control agencies, this may not filter down to the generalpopulation. This lack of understanding is particularly true for events that occurinfrequently; people are more aware of situations such as large floods and brush orforest fires that may occur every few years or decades (Figure 5.17). There are often

local ordinances to help avoid or minimize damages resulting from these events.For example, in some areas of southern California local regulations stipulate thathomes must be roofed with shingles that do not burn readily. Other regulations

Floodplain

Figure 5.16 Floodplain man-

agement Rapid City, South Dakota. A 1972 flood, prior to management,killed over 200 people and destroyedmany homes in the floodplain.Thefloodplain of Rapid Creek downstreamof Canyon Lake (center) is now thesite of a golf course (lower left).

(Courtesy of Perry Rahn)

Figure 5.17 Killer wildfire

Wildfire in October 1991 devastatedthis Oakland, California, neighbor-hood.This fire killed 25 people anddestroyed over 3,000 homes, with

damages of about $1.7 billion.(Tom Benoit/Getty Images Inc.)



include mandatoryinstallation of sprinkler systems andclearing lots of brush.Suchsafety measures are often noticeable during the rebuilding phase following a fire.

One of the most environmentally sound adjustments to hazards involves land-use planning. That is, people can avoid building on floodplains, in areas wherethere are active landslides, or in places where coastal erosion is likely to occur. Inmany cities, floodplains have been delineated and zoned for a particular land use.With respect to landslides, legal requirements for soil engineering and engineering

geology studies at building sites may greatly reduce potential damages. Damagesfrom coastal erosion can be minimized by requiring adequate setback of buildingsfrom the shoreline or seacliff. Although it may be possible to control physicalprocesses in specific instances, land-use planning to accommodate natural pro-cesses is often preferable to a technology-based solution that may or may not work.

Insurance. Inurance is another option that people may exercise in dealing withnatural hazards. Flood insurance and earthquake insurance are common in manyareas. However, because of large losses following the 1994 Northridge earth-quake, several insurance companies announced they would no longer offerearthquake insurance to residents of the area.

Evacuation. In the states along the Gulf of Mexico and along the eastern coast of

the United States, evacuation is an important option or adjustment to the hurri-cane hazard. Often, there is sufficient time for people to evacuate provided theyheed the predictions and warnings. However, if people do not react quickly andthe affected area is a large urban region, then evacuation routes may be blocked byresidents leaving in a last-minute panic. Successful evacuation from areas of volcanic eruptions is mentioned in Chapter 7.

Disaster Preparedness. Individuals, families, cities, states, or even entire nationscan practice disaster preparedness. Training individuals and institutions tohandle large numbers of injured people or people attempting to evacuate an areaafter a warning is issued is particularly important in disaster preparedness.

Artificial Control of Natural Processes

Attempts at artificial control of natural processes such as landslides, floods, and lavaflows have had mixed success. Seawalls constructed to control coastal erosion mayprotect property to some extentbut tend to narrow or even eliminatethebeach. Eventhe best designed artificial structures cannot be expected to adequately defendagainst an extreme event, although retaining walls and other structures that defendslopes from landslides have generally been successful when well designed (Fig-ure 5.18). Even the casual observer has probably noticed the variety of suchstructures along highways and urban land in hilly areas. These have limited impact


Figure 5.18 Protecting a slope

Retaining wall being constructedalong a canyon side in an area wherelandslides were formerly common.The wall protects the homes that wereconstructed too close to the edge of the steep canyon. If the homes werebuilt with adequate setback from thecanyon, the wall would not be

necessary. (Edward A. Keller)



on the environment but are necessary where construction demands that artificialcuts be excavated or where unstable slopes impinge on human structures. Commonmethods of flood control are channelization and construction of dams and levees.Unfortunately, flood controlprojects tendto providefloodplain residents witha falsesense of security; no method can be expected to absolutely protect people and theirpropertyfrom high-magnitude floods. We will return to this discussion in Chapter 8.

All too often people choose to simply bear the loss caused by a natural disaster.

Many people are optimistic about their chances of making it through any sort of disaster and take little action in their own defense, particularly for hazards such asvolcanic eruptions and earthquakes that occur only rarely in a particular area.Regardless of the strategy we choose either to minimize or to avoid hazards, it isimperative that we understand and anticipate hazards and their physical, biologi-cal, economic, and social impacts.

5.4 Global Climate and Hazards

Global and regional climatic change may significantly affect the incidence of haz-ardous natural events such as storms (floods and erosion), landslides, drought, andfires. Global warming associated with climatic change may also have an impact on

natural hazards. (We will discuss global warming in detail in Chapter 19.)How might a climatic change affect the magnitude and frequency of disastrous

natural events? As a result of global warming, sea level will rise as glacial ice meltsand warming ocean waters expand. This rise in sea level will lead to an increase incoastal erosion. With a change in climatic patterns, food production areas will shiftas some receive more precipitation and others less than they do now. Deserts andsemiarid areas would likely expand, and more northern latitudes could becomemore productive. Such changes could lead to global population shifts, whichcould precipitate wars or major social and political upheavals.

Global warming, with warming of the oceans of the world, will channel moreenergy from warmer ocean water into the atmosphere. Warming the atmospherewill likely increase the frequency and severity of hazardous weather-related

processes including thunderstorms, tornadoes, and hurricanes. The year 1998 set arecord for economic losses from weather-related disasters, causing about $100 bil-lion in economic losses worldwide. Losses from storms, floods, fires, and droughtsin 1998 (one of the warmest years on record) were greater than the losses forthe entire decade of the 1980s (Figure 5.19). Worldwide, the impact on peoplefrom weather-related disasters in 1998 was catastrophic, killing approximately32,000 people while displacing another 300 million people from their homes.9 Thetrend is clear—the number of severe weather events (storms, floods, drought, heatwaves, and cold) is increasing.

Global Climate and Hazards 153

L o s s

i n b i l l i o n s o

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l l a r s

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120

100

80

60

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20

0

800

700

600

500

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1980 1985 1990 1995 2000 2005

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N u m

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Figure 5.19 Severe weather

hazards increasing Worldwide num-ber of events and economic lossesfrom weather-related natural hazards(1980–2002). (Modified after Sawing, J. L.

2003. Vital Signs. New York: W. W. Norton.

World Watch Institute)



5.5 Population Increase, Land-Use Change,

and Natural Hazards

Population Increase and Hazardous EventsPopulation growth throughout the world is a major environmental problem. And,as our population increases, the need for planning to minimize losses from naturaldisasters also increases. Specifically, an increase in population puts a greaternumber of people at risk from a natural event; it also forces more people to settlein hazardous areas, creating additional risks. The risks of both high populationdensity and living in a danger zone are dramatically illustrated by the loss of thousands of lives in Colombia in 1985. (See A Closer Look: Nevado del Ruiz.)

Mexico City is another example of the risks associated with high populationdensity coupled with living in a dangerous zone. Mexico City is the center of theworld’s most populous urban area. Approximately 23 million people are concen-trated in an area of about 2,300 km2 (890 mi2) and about one-third of the familieslive in a single room. The city is built on ancient lake beds that accentuateearthquake shaking, and parts of the city have been sinking at the rate of a fewcentimeters per year owing in part to groundwater withdrawal. The subsidence

has not been uniform, so the buildings tilt and are even more vulnerable to theshaking of earthquakes.10 In September 1985, Mexico endured a large damagingearthquake that killed about 10,000 people in Mexico City alone.

Land-Use Change and Hazardous EventsDuring the 1990s there was a record number of great catastrophes worldwide.Although there are over 500 disasters from natural hazardous events each year,only a few are classified as a great catastrophe, which is one that results in deaths orlosses so great that outside assistance is required.11 During the past half-century,there hasbeen a dramatic increase in great catastrophes, as illustrated in Figure 5.20.For these events, flooding is the major killer of people, followed by earthquakes,volcanic eruptions, and windstorms. From 1985 to 1995 over 550,000 people died asa result of natural hazards. The vast majority of deaths (96 percent) were in thedeveloping countries. Asia suffered the greatest losses from 1985 to 1997, with77 percent of the total deaths and 45 percent of the economic losses. It could have

been even worse from 1985 to 1999, were it not for improvements in warning,disaster preparedness, and sanitation following disasters.11 Nevertheless, economiclosses have increased at a much faster rate than have the number of deaths.

Three of the deadly catastrophes resulting from natural hazards linked tochanges in land use were Hurricane Mitch in 1998, which devastated CentralAmerica; the 1998 flooding of the Yangtze River in China; and Hurricane Katrina in2005. Hurricane Mitch caused approximately 11,000 deaths, and the floods in theYangtze River resulted in nearly 4,000 deaths. It has been speculated that damagesfrom these events in Central America and China were particularly severe because

of land-use changes that had occurred. For example, Honduras has already lostnearly half of its forests owing to timber harvesting, and a fire with an area of about11,000 km2 ( 4,250 mi2) occurred in the region before the hurricane.As a result of theprevious deforestation and the fire, hillsides were stripped of vegetation andwashedaway; along with them went farms,homes, roads, andbridges (Figure 5.21).The story is similar in central China; recently, the Yangtze River basin lost about85 percent of its forest as a result of timber harvesting and conversion of land to agri-culture. As a result of theland-use changes in China,flooding of theYangtzeRiver isprobably much more common than it was previously.9 Hurricane Katrina (see casehistory opening this chapter) emphasized several poor land-use choices, includingthe removal of coastal wetlands that provide a buffer to wind and storm waves.

The hazardous events that caused catastrophes in the late 1990s and early

twenty-first century in Central America, China, the United States, and other partsof the world may be early warning signs of things to come. It is apparent that




Population Increase, Land-Use Change, and Natural Hazards 155

1 9 5 0 s

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i c l o s s e s

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f d o

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)

Figure 5.20 Disasters are

increasing Major disasters from the1950s to the 1990s. (a) Economiclosses and (b) number of major catas-trophes. (Data from Abramovitz,

J. N. 2001. Averting unnatural disasters.

In Brown, L. R., et al. State of the world.

2001, pp. 123–42. Worldwatch Institute.

New York: W. W.Norton)

Figure 5.21 Hurricane disaster

Homes destroyed by flooding andlandslides in Honduras fromHurricane Mitch in 1998. (Luis

Elvir/AP/Wide World Photos)




A CLOSER LOOK

Nevado del Ruiz: A Story of People, Land Use,and Volcanic Eruption

A fundamental principle of this chapter is that populationincrease, coupled with land-use change, has intensified

impacts of natural hazards. In some cases, disasters from nat-ural hazards have become catastrophes. For example, whenthe Colombian volcano Nevado del Ruiz erupted in 1845, amudflow roared down the east slope of the mountain, killingapproximately 1,000 people. Deposits from that eventproduced rich soils in the Lagunilla River valley, and an agri-cultural center developed there. The town that the areasupported was known asArmero, and by 1985 itwas a prosper-ous community with a growing population of about 23,000people. On November 13, 1985, another mudflow associatedwith a volcanic eruption buried Armero, leaving about 21,000peopledead or missing while inflicting more than $200 millionin property damage. It was population increase during the140 years between the mudflows that multiplied the death toll by more than 20 times. The flat lands and rich soil produced bythe previous volcanic eruption lured people into a hazardousarea. Ironically, the area was decimated by the same type of event that had earlier produced productive soils, stimulatingdevelopment and population growth.12

The volcanic eruption of November 13, 1985, followed ayear of precursor activity, including earthquakes and hot-spring activity. Volcano monitoring began in July 1985, and inOctober a hazards map was completed that correctly identi-fied the events that occurred on November 13. The reportand accompanying map gave a 100 percent probability that

potentially damaging mudflows would be produced by aneruption, as had been the case with previous eruptions.

The November 13 event, as expected, started with anexplosive eruption that produced pyroclastic flows of hot vol-canic ash that scoured and melted glacial ice on the mountain.The ash and melting glacial ice produced water that gener-ated mudflows that raced down river valleys. Figure 5.Cshows the areas affected by magma that came into contactwith water or ice, causing violent steam and ash explosions,called base surges, and pyroclastic flows. It also shows thelocation of glacial ice that contributed the water necessary toproduce the mudflows. Of particular significance was themudflow that raced down the River Lagunillas and destroyedpart of the town of Armero, where most of the deathsoccurred. Figure 5.D shows the volcano and the town of Armero. Mudflows buried the southern half of the town,sweeping buildings completely off their foundations.13

The real tragedy of the catastrophe was that the outcomewas predicted; in fact, there were several attempts to warn thetown andevacuate it. Hazard maps were circulated in October, but they were largely ignored. Figure 5.E shows the hazardmapof events expected before the eruption and the events thatoccurred. This graphically illustrates the usefulness of volcanicrisk maps.14 Despite these warnings there was little response,and as a result approximately 21,000 people died. Early in 1986a permanent volcano observatory center was established inColombia to continue monitoring the Ruiz volcano as well as

Figure 5.C Eruption of

Nevado del Ruiz Map of the volcano Nevado del Ruiz area,showing some of the featuresassociated with the eruption ofNovember 13, 1985. (Modified after

Herd, D. G. 1986. The Ruiz volcano

disaster. EOS, Transactions of the

American Geophysical Union,

May 13: 457–60)

0 5 km

N

November 13, 1985, eruption

Base surges—pyroclastic flows

Extent of glacialice before eruption

Maximum extent

Direction of movement

Mudflows R.

G u a l i

R . Mo l i no s

R. G u a l i

R. A z u f r a d

o

R. L a g

u n i l l a

s

R. Recio

R . R e c i o

Q .

A g u a

c a l i e n t e

Q . L a s N e r e i d a s

Q . L i s a

Craterarenas

NEVADO

DEL RUIZ



Population Increase, Land-Use Change, and Natural Hazards 157

Figure 5.D Nevado del Ruiz (a) The volcano before the eruption. (Photo El Espectador/Corbis/Sygma)

(b) Catastrophic mudflow: The eruption generated a mudflow that nearly destroyed the town of Armero,killing 21,000 people. (J. Langevin/Corbis/Sygma)

(a) (b)

Actual extentof ash fall

Herveo

High ash-fallhazard

M o d e r a t e a s h - f a l l h a z a r d 0 15 KILOMETERS

Venadillo

La SierraAmbalema

Lerida

El Libano

GuayabalMendez

Armero

Villa

Hermosa

Manizales

Villamaria

R e c i o

Riv e r

G u a l i R

i v e r

A z u

f r a d o

R

L a n g u n i l l a s R i v e r

S a b

a ndi j a R i v e r

M a

g d

a l e

n a

R i v e r

C h i n c h i n á R Nevado

delRuiz

High lava-flowhazard

Moderate lava-flowhazard

High pyroclastic-flow hazard

Moderate pyroclastic-flow hazard

High mudflowhazard

Mudflows from November 1985eruption of Nevado del Ruiz

EXPLANATION

Figure 5.E Volcanic hazard map

Produced and circulated 1 monthbefore the November 13, 1985,eruption of Nevado del Ruiz andmudflows that buried Armero,Colombia.The actual mudflow

deposits are shown in red. (Wright, T. L.,

and Pierson, T. C. 1992. U.S. Geological

Survey Circular 1973)

others in South America. South America should now be betterprepared to dealwithvolcanic eruptions. Had there beenbettercommunication lines from civil defense headquarters to localtowns and a better appreciation of potential volcanic hazards

even 40 km (about 25 mi) from the volcano, evacuation wouldhave been possible for Armero. It is hoped that the lessonslearned from this event will help minimize future loss of lifeassociated with volcanic eruptions and other natural disasters.

human activities are likely increasing the impacts of natural disasters. In recogni-tion of the influence of human activities, China has banned timber harvesting inthe upper Yangtze River basin, has prohibited imprudent floodplain land uses,and has allocated several billion dollars for reforestation. The lesson being learnedis that if we wish to minimize damages from natural hazards in the future, weneed to consider land rehabilitation. The goal must be to achieve sustainable



Revisiting Fundamental Concepts

Human Population Growth

Increase in human population is forcing many people to livein areas where natural hazards are more likely, as for exampleon floodplains, steep slopes, and flanks of volcanoes. Popula-tion pressure has accelerated land-use changes as more landis urbanized, farmed, mined, and harvested for timber. As a

result, hazardous events that were formerly disasters are becoming catastrophes.

Sustainability

Living in hazardous areas such as on floodplains is not asustainable practice, as communities willcontinue tosufferprop-erty damage and loss of life. Ensuring that future generationsinherit a quality environment requires that we minimize lossesfrom natural hazards. We cannot sustain soil resources if we

continue to log forests on steep slopes, thereby increasing theoccurrenceof landslides and floodingthaterode soil.

SUMMARY

Our discussion of natural processes suggests a view of natureas dynamic and changing. This understanding tells us thatwe cannot view our environment as fixed in time. A land-scape without natural hazards would also have less variety;it would be safer but less interesting and probably lessaesthetically pleasing. The jury is still out on how muchwe should try to control natural hazards and how much weshould allow them to occur. However, we should rememberthat disturbance is natural and that management of naturalresources must include management for and with distur- bances such as fires, storms, and floods.

A fundamental principle of environmental geology is thatthere have always been Earth processes dangerous to people.These become hazards when people live close to the source of danger or when they modify a natural process or landscape ina way that makes it more dangerous. Natural events that willcontinue to cause deaths and property damage include flood-ing, landslides, earthquakes, volcanic activity, wind, expansivesoils, drought, fire, and coastal erosion. The frequency of a haz-ardous event is generally inversely related to its magnitude; itsimpact on people depends on its frequency and magnitude aswell as on such diverse factors as climate, geology, vegetation,and human use of the land. The same natural events that createdisasters may also bring about benefits, as when river flooding

or a volcanic eruption supplies nutrients to soils.The events causing the greatest number of deaths in the

United States are tornadoes and windstorms, lightning,floods, and hurricanes, although a single great earthquake cantake a very large toll. Floods, landslides, frost, and expansivesoils cause the greatest property damage. Events most likelyto produce a catastrophe are floods, hurricanes, tornadoes,earthquakes, volcanic eruptions, and fires. Although in theUnited States land-use changes, urbanization, and populationincrease are causing damages from most hazards to increase, better predictions and warning systems are reducing thenumber of deaths from these hazardous processes.

Some disastrous events can be forecasted or predictedfairly accurately, including some river floods and the arrivalof coastalhurricanes and tsunamis. Precursor eventscanwarnexperts about impending earthquakesand volcanic eruptions.

Once an event has been forecasted or predicted, this informa-tion must be made available to planners and decision makersin orderto minimizethethreatto human life andproperty. Themanner in which a warning is issued and how scientistscommunicate with the media and public are particularlysignificant. For many hazards we cannot determine when aspecificevent will occur butonlythe probability of occurrence, based on the record of past occurrences. The risk associatedwith an event is theproduct of the event’s probability of occur-rence and the likely consequences should it actually occur.

The impact of a disaster upon a population includes directeffects—people killed, dislocated, or otherwise damaged—and indirect effects—emotional distress, donation of moneyor goods, and paying taxes to finance recovery. Recoveryoften has several stages, including emergency work, restora-tion of services and communication, and reconstruction.

The options that individuals or societies choose for avoid-ing or adjusting to natural hazards depend in part on howhazards are perceived. People tend to be more aware of hazards that are likely to occur often, such as the several hurri-canes in the Atlantic that could strike the East and Gulf Coastsof North America each year. Options to adjust to hazards rangefrom land-use planning, insurance, and evacuation to disasterpreparedness and artificial control of natural processes. For

hazards that occur rarely in particular areas, people oftenchoose to just bear the loss incurred from the hazard. Attemptsto artificially control natural processes have had mixed successand usually cannot be expected to defend against extremeevents. Regardless of the approach we choose, we mustincrease our understanding of hazards and do a better job of anticipating them.

As the world’s population increases and we continue tomodify our environment through changes such as urbaniza-tion and deforestation, more people will live on marginallands and in more hazardous locations. As a result of popula-tion pressure and land-use changes, what were formerlylocalized hazards and disasters are now becoming catastro-phes. Therefore, as population increases, better planning at alllevels will be necessary if we are to minimize losses fromnatural hazards.

development based on both restoration and maintenance of healthy ecosystems.9

This goal will be difficult to reach given the pressures of human populationgrowth in many parts of the world. The effects of population increase emphasizethe need to control human population growth if we are to solve pressing environ-mental problems and reach our goal of sustaining our environment.




Critical Thinking Questions 159

Key Terms

catastrophe (p. 141)

disaster preparedness (p. 152)

fault gouge (p. 138)

forecast (p. 145)

land-use planning (p. 152)

magnitude-frequency concept (p. 138)

precursor events (p. 146)

risk (p. 148)

warning (p. 147)

Review Questions

1. What were the two main lessonslearned from the 1985 eruption of Nevado del Ruiz in Colombia?

2. What is a catastrophe, and howdoes it differ from a disaster?

3. What do we mean by the magni-

tude and frequency of a naturalprocess?

4. What is the main conclusion fromthe magnitude-frequency concept?

5. What is the role of history inunderstanding natural hazards?

6. List some potential linkages between hazardous events.

7. What are some of the methodsof predicting where a disaster islikely to occur?

8. What is the difference between a

forecast and prediction?9. Why do you think there sometimes

are strained relationships betweenthe media and scientists?

10. How may the risk of a particularevent be defined?

11. What is the difference between areactive response and an anticipa-tory response in hazard reduction?

12. What are some of the commonadjustments that limit or reducethe effects of natural hazards?

13. What is the role of global climatein the occurrence of naturalhazardous events?

14. How does human populationincrease result in disasters becoming catastrophes?

Earth as a System

Dynamic Earth systems such as the atmosphere, hydrosphere,and lithosphere are responsible for producing processesthat are hazardous to people. Change in one part of a systemaffects other parts, often in a complex way. For example, burning fossil fuels is releasing carbon dioxide into the atmos-phere, causing global warming. One result is that some places

will receive more rain and experience more violent storms.These increases will cause changes in the intensity of floodsand landslide activity.

Scientific Knowledge and Values

Intensive study of hazardous Earth processes has greatlyincreased our knowledge of where these processes occur, how

they work, the damages they do, and how best to minimizedamages. People’s values, coupled with the scientific knowl-edge, will determine in part the choices we make to reducethe impact of hazardous events. For example, study of hospi-tals andschools in an earthquake-proneregionmay revealthatmany are old and likely to fail during a large earthquake.Fixing the hospitals and schools to withstand shaking is a

logical answer, but it may cost billions of dollars. Our value of human life compared with other values will determinewhether we spend the money to do the necessary work tostrengthenthe hospitals and schools.

Critical Thinking Questions

1. List all the natural processes thatare hazardous to people and prop-erty in the region where you live.What adjustments have you andthe community made to lessen theimpacts of these hazards? Couldmore be done? What? Whichalternatives are environmentallypreferable?

2. Assume that in the future we will be able to predict with a givenprobability when and where alarge damaging earthquake will

date is quite low, say 10 percent,should the general public beinformed of the forecast? Shouldwe wait until a 50 percent confi-dence or even a 90 percentconfidence is assured? Does thelength of time between the fore-cast and the event have any bearing on your answers?

3. Find a friend, and one of you takethe role of a scientist and anothera news reporter. Assume that thenews reporter is interviewing

your town. After the interview, jotdown some of your thoughts con-cerning ways in which scientistscommunicate with newspeople.Are there any conflicts?

4. Develop a plan for your commu-nity to evaluate therisk of flooding.How would you go aboutdetermining an acceptable risk?

5. Do you agree or disagree thatland-use change and populationincrease are increasing the riskfrom natural processes? Develop a

ch05 earth processes and natural hazards

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