NATURAL HAZARDS

ATMOSPHERIC HAZARDS

I.  Tropical Cyclones

Tropical cyclones defined as a low pressure area of closed circulation winds that originates over tropical waters.  Winds rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.  The season lasts from June through November. 

Danger Zones- The most devastating naturally occurring hazards in the United States and it territories usually developing over the warm waters of the Gulf of Mexico, Caribbean Sea, and Atlantic Ocean. 

Types of tropical cyclones include: 

Hurricanes - A hurricane is a tropical storm with winds that have reached a constant speed of 74 miles per hour or more. Hurricane winds blow in a large spiral around a relative calm center known as the “eye.” The “eye” is generally 20 to 30 miles wide, and the storm may extend outward 400 miles. As a hurricane approaches, the skies will begin to darken and winds will grow in strength. As a hurricane nears land, it can bring torrential rains, high winds, and storm surges. A single hurricane can last for more than 2 weeks over open waters and can run a path across the entire length of the eastern seaboard. August and September are peak months during the hurricane season, that lasts from June 1 through November 30.

Tropical Storms - A tropical storm is a warm core tropical cyclone in which the maximum sustained surface wind speed ranges from 39 to less than 74 mph

Typhoons - A tropical cyclones are called typhoons in the western North Pacific basin and after winds sustain speeds of 150 mph or greater are classified as super typhoons

II. Thunderstorms 

Thunderstorms can bring heavy rains (which can cause flash flooding), strong winds, hail, lightning and tornadoes. Thunderstorms are generated by atmospheric imbalance and turbulence due to the combination of conditions: 

a) Unstable warm air rising rapidly into the atmosphere
b) Sufficient moisture to form clouds and rain
c) Upward lift of air currents caused by colliding weather fronts (cold and warm), sea breezes, or mountains

Thunderstorms may occur singly, in clusters or in lines. Thus, it is possible for several thunderstorms to affect one location in the course of a few hours. Some of the most severe weather occurs when a single thunderstorm affects one location for an extended time.

Lightning is a major threat during a thunderstorm. In the United States, between 75 to 100 Americans are hit and killed each year by lightning.  Lightening is classified severe if its winds reach or exceed 58 mph, produces o tornado, or drops surface hail at least 0.75” in diameter.

Lightning facts:

· Significant airplane disasters often are associated with thunderstorms and lightning.
· It is a myth that lightning never strikes twice in the same place. In fact, lightning will strike several times in the same place in the course of one discharge.
· A bolt of lightning reaches a temperature approaching 50,000 degrees Fahrenheit in a split second.
Danger Zone- While thunderstorms and lightning can be found throughout the United States, they are most likely to occur in the central and southern states. The state with the highest number of thunderstorm days is Florida. 
 

III.  Tornadoes 

Tornadoes are a rapidly rotating vortex or funnel of air extending ground ward from a cumulonimbus cloud. 

1) Approximately 1,000 tornadoes are spawned by thunderstorms each year
2) Most tornadoes remain aloft, the danger is when it touches the ground.  It can lift and move huge objects, destroy or move whole buildings long distances, and siphon large volumes from bodies of water
3) The most susceptible states (tornado alley) are Texas, Oklahoma, Arkansas, Missouri, and Kansas
4) Tornadoes follow the path of least resistance.  People living in valleys, have the greatest exposure.
5) They tend to occur in the afternoons and evenings:  over 80 percent of all tornadoes strike between noon and midnight
6) Over the past 20 years, there has been 106 Federal disaster declarations for damage due to tornadoes

Danger Zones- Tornadoes can occur in any state but are more frequent in the Midwest, Southeast and Southwest. The states of Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Iowa, Kansas, Louisiana, Mississippi, Missouri, Nebraska, Oklahoma, South Dakota, and Texas are at greatest risk.

Fujita - Pearson Tornado Scale

F-0: 40-72 mph, chimney damage, tree branches broken
F-1: 73-112 mph, mobile homes pushed off foundation or overturned
F-2: 113-157 mph, considerable damage, mobile homes demolished, trees uprooted
F-3: 158-205 mph, roofs and walls torn down, trains overturned, cars thrown
F-4: 207-260 mph, well-constructed walls leveled
F-5: 261-318 mph, homes lifted off foundation and carried considerable distances, autos thrown as far as 100 meters

IV.  Windstorms
Extreme windstorm events are associated with extra tropical and tropical cyclones, and severe thunderstorms.  Winds vary from zero at ground level to 200 mph in the upper atmosphere.  Over the past 20 years, Federal disaster declarations involved wind-induced damage. 

Danger Zones - Areas experiencing the highest wind speeds are:
· Coastal regions from Texas to Maine, under the influence of North Atlantic Ocean and Gulf of Mexico hurricane-related windstorms
· The Alaskan coast, under the influence of winter low-pressure systems in the Gulf of Alaska and North Pacific Ocean.
· Isolated wind phenomena in the Western States, such as the Chinook and Santa Ana winds, occur very locally along mountainous terrains.

V.  Hailstorms 

A Hailstorm is an outgrowth of a severe thunderstorm in which balls or irregularly shaped lumps of ice greater than 0.75” in diameter fall with rain. 

· Hailstorms occur more frequently during late spring and early summer, when the jet stream migrates northward across the Great Plains.
· Hailstorms cause nearly $1 billion in property and crop damage annually.

Danger Zones- Hailstorms occur primarily in the Midwestern States.  Only a localized area along the border of northern Colorado and southern Wyoming experiences hailstorms on 8 or more days each year.  Most inland regions experience hailstorms at least 2 or more days each year.

VI. Snow Avalanches

A snow avalanche is the sliding snow or ice mass in an avalanche moves at high velocities.  It can sheer trees, completely cover entire communities and highway routes, and level buildings.  Natural and human-induced snow avalanches most often result from structural weaknesses within the snow pack.  The potential for a snow avalanche increases with significant temperature influences.

The primary threat is loss of life of backcountry skiers, climbers, and snowmobilers due to suffocation when buried in an avalanche.  Around 10,000 avalanches are reported each year.  Since 1790, an average of 144 persons have been trapped in avalanches annually: on average 14 injured and 14 died.  The estimated annual average damage to structures is $500,000.

Danger Zones- The threat is most severe in the mountainous Western United States, including Alaska. 

VII. Severe Winter Storms

Severe Winter Storms consist of extreme cold and heavy concentrations of snowfall or ice.  A blizzard combines heavy snowfall, high winds, extreme cold, and ice storms.  The origins of the weather patterns are from four sources:

1) In the Northwestern States, cyclonic weather systems form the North Pacific Ocean or the Aleutian Island region sweep massive low-pressure systems with heavy snow and blizzards. 
2) In the Midwestern and Upper Plains States, Canadian and Arctic cold fronts push ice and snow deep into the interior region and, in some instances, all the way down to Florida.
3) In the Northeast, lake effect snowstorms develop from the passage of cold air over the relatively warm surfaces of the Great Lakes, causing heavy snowfall and blizzard conditions.
4) The Eastern and Northeastern States are affected by extra-tropical cyclonic weather systems in the Atlantic Ocean and Gulf of Mexico that produce snow, ice storms, and occasional blizzards.

Danger Zone – Severe Winter Storms affect every State in the continental United States and Alaska.  Areas where such weather is rare, such as the extreme South, are disrupted more severely by winter storms than are regions that experience severe weather more frequently.  An average of 93 deaths are attributed to winter storms annually. 

IX.  Extreme Heat 

Extreme Heat is temperatures that hover 10 degrees or more above the average high temperature for the region and last for several weeks. Humid or muggy conditions, which add to the discomfort of high temperatures, occur when a “dome” of high atmospheric pressure traps hazy, damp air near the ground. Excessively dry and hot conditions can provoke dust storms and low visibility. Droughts occur when a long period passes without substantial rainfall. A heat wave combined with a drought is a very dangerous situation.

Danger Zones- All areas in the United States are at risk of drought at any time of the year. Drought gripped much of the West and Midwest from 1987 to 1991. The Missouri River Basin and California have experienced extended periods of drought as well.

GEOLOGIC HAZARDS

Geologic Hazards are non-seismic ground failures involving landslides, land subsidence, and expansive soils. 

I.  Landslides 

Landslides occur when masses of rock, earth, or debris move down a slope. Landslides may be very small or very large, and can move at slow to very high speeds. Many landslides have been occurring over the same terrain since prehistoric times. They are activated by storms and fires and by human modification of the land. New landslides occur as a result of rainstorms, earthquakes, volcanic eruptions, and various human activities.

Mudflows - Mudflows (or debris flows) are rivers of rock, earth, and other debris saturated with water. They develop when water rapidly accumulates in the ground, such as during heavy rainfall or rapid snowmelt, changing the earth into a flowing river of mud or “slurry.” A slurry can flow rapidly down slopes or through channels, and can strike with little or no warning at avalanche speeds. A slurry can travel several miles from its source, growing in size as it picks up trees, cars, and other materials along the way.
Lateral Spreads- Lateral Spreads are large elements of distributed, lateral displacement of materials They occur in rock, but they can also occur in fine-grained, sensitive soils such as quick clays.  Loose granular soils commonly produce lateral spreads through liquefaction.  Liquefaction can occur spontaneously, presumably because of changes in pore-water pressures, or in response to vibrations such as those produced by strong earthquakes.
Falls and Topples - Falls occur when masses of rock or other material detach from a steep slope or cliff and descend by free fall, rolling, or bouncing.  Topples consist of the forward rotation of rocks or other materials about a pivot point on a hill slope. 

II.  Land Subsidence 

Land Subsidence is the loss of surface elevation due to the removal of subsurface support, ranges from broad, regional lowering of the land surface to localized collapse.  The primary cause of most subsidence is human activities:  underground mining of coal, groundwater or petroleum withdrawal, and drainage of organic soils.

The average annual damage from all types of subsidence is conservatively estimated to be at least $125 million. 

· Collapse into Voids- Collapse of surficial materials into underground voids is the most dramatic form of subsidence usually from coalmines.
· Sediment Compaction - Sediment compaction typically causes broad regional subsidence.  Rates of subsidence usually are low, ranging from a few millimeters to centimeters per year.

III.  Expansive Soils 

Soils and soft rock that tend to swell or shrink due to changes in moisture content are commonly known as expansive soils.  Changes in soil volume present a hazard primarily to structures built on top of expansive soils.  The most extensive damage occurs to highways and streets.  Two major groups of rocks, which occur more commonly in the West than East:

· Aluminum Silicate Minerals – ash, glass, and rocks of volcanic origin
· Sedimentary Rock – clay minerals, shale
 

HYDROLOGIC HAZARDS

Water related damage caused by flooding along rivers and coasts in the U.S. accounts for over 75 percent of all Federal disaster declarations. 

I.  Floods 

Floods can be slow, or fast rising but generally develop over a period of days.  It usually occurs from large-scale weather systems generating prolonged rainfall or on-shore winds.  Other causes of flooding include locally intense thunderstorms, snowmelt, ice jams, and dam failures.  Floods are capable of undermining buildings and bridges, eroding shorelines and riverbanks, tearing out trees, washing out access routes, and causing loss of life and injuries.

Flash floods usually result from intense storms dropping large amounts of rain within a brief period. Flash floods occur with little or no warning and can reach full peak in only a few minutes. 

Danger Zone - Floods are the most common and widespread of all natural disasters—except fire. Most communities in all 50 states can experience some kind of flooding after spring rains, heavy thunderstorms, or winter snow thaws.  The states with the greatest risk are Florida, California, Texas, Louisiana, and New Jersey.  (FEMA bases that on a composite risk score that accounts for floodplain are and number and value of households)
Flooding Facts:
· Flooding has caused the deaths of more than 10,000 people since 1900.
· Property damage from flooding now totals over $1 billion each year in the United States. 
· FEMA estimates that over 9 million households and $390 billion in property are at risk from flooding.
II.  Storm Surges 

Storm Surges are storms that generate the large waves on the coast that cause coastal flooding and erosion.  They are most frequent from late fall to early spring, but can develop year-round.  They are usually associated with extra tropical cyclones (nor’easters) in the North Atlantic Ocean and the Gulf of Mexico, and severe winter low-pressure systems in the North Pacific Ocean and the Gulf of Alaska.

Danger Zone- The entire East Coast, along the Gulf of Mexico, the California Coast, and the Gulf of Alaska
 
 

III.  Coastal Erosion 

Coastal erosion is measured as the rate of change in the position or horizontal displacement of a shoreline over a period of time.  It is generally associated with storm surges, hurricanes, windstorms, and flooding hazards, and may be exacerbated by human activities such as boat wakes, shoreline hardening, and dredging.

Danger Zones- It affects every coastal State and territory in the U.S.

Coastal erosion has been a factor in more than 25 Federal disaster declarations during the past 20 years.

IV.  Droughts 

Drought is defined as a water shortage caused by a deficiency of rainfall and differs from other natural hazards in three ways:
a) A drought’s onset and end are difficult to determine since the effects accumulate slowly and may linger even after the apparent termination of an episode.
b) The absence of a precise and universally accepted definition adds to the confusion about whether a drought exists, and if it does, the degree of severity.
 c) Drought impacts are less obvious and spread over a larger geographic area.
 

SEISMIC HAZARDS

I.  Earthquakes

An earthquake is a sudden, rapid shaking of the Earth caused by the breaking and shifting of rock beneath the Earth’s surface. This shaking can cause buildings and bridges to collapse; disrupt gas, electric, and phone service; and sometimes trigger landslides, avalanches, flash floods, fires, and huge, destructive ocean waves (tsunamis). Buildings with foundations resting on unconsolidated landfill, old waterways, or other unstable soil are most at risk.  Earthquakes can occur at any time of the year.

Danger Zones - Earthquakes occur most frequently west of the Rocky Mountains, although historically the most violent earthquakes have occurred in the central United States. All 50 states and all U.S. territories are vulnerable to earthquakes. Forty-one states or territories are at moderate to high risk.

Many people think of California as “Earthquake Country,” but the state with the most major earthquakes is Alaska. 

II.  Tsunami (pronounced “soo-nahm’ee”)

A tsunami is a series of waves generated by an undersea disturbance such as an earthquake. From the area of the disturbance, the waves will travel outward in all directions, much like the ripples caused by throwing a rock into a pond.  As the waves approach the shallow coastal waters, they appear normal and the speed decreases. Then as the tsunami nears the coastline, it may grow to great height and smash into the shore, causing much destruction.
a)  Areas at greatest risk are less than 50 feet above sea level and within one mile of the shoreline.
b)  Tsunamis arrive as a series of successive “crests” (high water levels) and “troughs” (low water levels). These successive crests and troughs can occur anywhere from 5 to 90 minutes apart. They usually occur 10 to 45 minutes apart.  The wave speed in the open ocean will average 450 miles per hour. 
c)  Tsunamis reaching heights of more than 100 feet have been recorded.
d)  Most deaths during a tsunami are a result of drowning. Associated risks include flooding, polluted water supplies, and damaged gas lines.
 

OTHER NATURAL HAZARDS

I.  Volcanic

A volcano is a mountain that opens downward to a reservoir of molten rock below the surface of the earth. Unlike most mountains, which are pushed up from below, volcanoes are built up by an accumulation of their own eruptive products lava, ash flows, and airborne ash and dust. When pressure from gases and the molten rock becomes strong enough to cause an explosion, eruptions occur. Gases and rock shoot up through the opening and spill over, or fill the air with lava fragments. Volcanic products are used as building or road-building materials, as abrasive and cleaning agents, and as raw materials for many chemical and industrial uses. Lava ash makes soil rich in mineral nutrients.
1. Volcanic ash can affect people hundreds of miles away from the cone of a volcano. Several of the deaths from the Mount St. Helens volcano in 1980 were attributed to inhalation of ash. Volcanic ash can contaminate water supplies, cause electrical storms, and collapse roofs. 
2. An erupting volcano can also trigger tsunamis, flash floods, earthquakes, rock falls, and mudflows. 
3. Sideways directed volcanic explosions, known as “lateral blasts,” can shoot large pieces of rock at very high speeds for several miles. These explosions can kill by impact, burial, or heat. They have been known to knock down entire forests. The majority of deaths attributed to the Mount St. Helens volcano were a result of lateral blast and tree blow-down. 
Danger Zones- Volcanic eruptions are most likely in the Pacific Rim states of Hawaii, Alaska, Washington, Oregon, and California. The chance of eruptions that could damage populated areas is the greatest for the active volcanoes of Hawaii and Alaska. Active volcanoes of the Cascade Mountain Range in California, Oregon, and Washington have created problems recently. The danger area around a volcano covers approximately a 20-mile radius. Some danger may exist 100 miles or more from a volcano, leaving Montana and Wyoming at risk. 
II.  Wildfires 

There are three different classes of wildland fires. A surface fire is the most common type and burns along the floor of a forest, moving slowly and killing or damaging trees. A ground fire is usually started by lightning and burns on or below the forest floor. Crown fires spread rapidly by wind and move quickly by jumping along the tops of trees. Wildland fires are usually signaled by dense smoke that fills the area for miles around.
a)  As residential areas expand into relatively untouched wildlands, people living in these communities are increasingly threatened by forest fires. Protecting structures in the wildland from fire poses special problems, and can stretch firefighting resources to the limit. 
b)  If heavy rains follow a fire, other natural disasters can occur, including landslides, mudflows, and floods. Once ground cover has been burned away, little is left to hold soil in place on steep slopes and hillsides. 
c)  A major wildland fire can leave a large amount of scorched and barren land. These areas may not return to pre-fire conditions for decades. If the wildland fire destroyed the ground cover, then erosion becomes one of several potential problems. 
Danger Zones-  all wooded, brush, and grassy areas—especially those in Kansas, Mississippi, Louisiana, Georgia, Florida, the Carolinas, Tennessee, California, Massachusetts, and the national forests of the western United States. 
 Interface or intermix fires –
 Firestorms –
 Prescribed fires and prescribed natural fires –
 

TECHNOLOGICAL HAZARDS

I.  Dam Failures 

Dam failures are potentially the worst flood events. A dam failure is usually the result of neglect, poor design, or structural damage caused by a major event such as an earthquake. When a dam fails, a gigantic quantity of water is suddenly let loose downstream, destroying anything in its path.

II.  Fires 

Fires can be triggered or exacerbated by lightning, high winds, earthquakes, volcanoes, and floods.  Lightning is the most significant natural contributor to fires affecting the built environment.  Buildings with rooftop storage tanks for flammable liquids are particularly susceptible. 

Danger Zones- States with the largest populations tend to have the greatest number of fire-related fatalities, which are related to population density. 

III.  Hazardous Materials Events 

Hazardous materials are chemical substances, which if released or misused can pose a threat to the environment or health. These chemicals are used in industry, agriculture, medicine, research, and consumer goods. Hazardous materials come in the form of explosives, flammable and combustible substances, poisons, and radioactive materials. These substances are most often released as a result of transportation accidents or because of chemical accidents in plants.
a)  Hazardous materials in various forms can cause death, serious injury, long-lasting health effects, and damage to buildings, homes, and other property. Many products containing hazardous chemicals are used and stored in homes routinely. These products are also shipped daily on the nation’s highways, railroads, waterways, and pipelines. 
b)  Varying quantities of hazardous materials are manufactured, used, or stored at an estimated 4.5 million facilities in the United States—from major industrial plants to local dry cleaning establishments or gardening supply stores. 
c)  The Emergency Planning and Community Right-to-Know Act requires that detailed information about hazardous substances in or near communities be available at the public’s request. The law provides stiff penalties for companies that fail to comply and allows citizens to file lawsuits against companies and government agencies to force them to obey the law. 

IV.  Nuclear Accidents
The potential danger from an accident at a nuclear power plant is exposure to radiation. This exposure could come from the release of radioactive material from the plant into the environment, usually characterized by a plume (cloud-like) formation. The area the radioactive release may affect is determined by the amount released from the plant, wind direction and speed and weather conditions (i.e., rain, snow, etc.) which would quickly drive the radioactive material to the ground, hence causing increased deposition of radionuclides.  Radioactive materials are composed of atoms that are unstable. An unstable atom gives off its excess energy until it becomes stable. The energy emitted is radiation. The process by which an atom changes from an unstable state to a more stable state by emitting radiation is called radioactive decay or radioactivity.
a)  Since 1980, each utility that owns a commercial nuclear power plant in the United States has been required to have both an onsite and offsite emergency response plan as a condition of obtaining and maintaining a license to operate that plant. Onsite emergency response plans are approved by the Nuclear Regulatory Commission (NRC). Offsite plans (which are closely coordinated with the utility’s onsite emergency response plan) are evaluated by the Federal Emergency Management Agency (FEMA) and provided to the NRC, who must consider the FEMA findings when issuing or maintaining a license.
b)  Radioactive materials—if handled improperly—or radiation accidentally released into the environment, can be dangerous because of the harmful effects of certain types of radiation on the body. The longer a person is exposed to radiation and the closer the person is to the radiation, the greater the risk. 
c)  Although radiation cannot be detected by the senses (sight, smell, etc.), it is easily detected by scientists with sophisticated instruments that can detect even the smallest levels of radiation. 
V.  National Security Hazards 
Terrorism is the use of force or violence against persons or property in violation of the criminal laws of the United States for purposes of intimidation, coercion or ransom. Terrorists often use threats to create fear among the public, to try to convince citizens that their government is powerless to prevent terrorism, and to get immediate publicity for their causes.
a)  Before the September 11, 2001 attacks in New York and the Pentagon, most terrorist incidents in the United States have been bombing attacks, involving detonated and undetonated explosive devices, tear gas and pipe and firebombs. 
b)  The effects of terrorism can vary significantly from loss of life and injuries to property damage and disruptions in services such as electricity, water supply, public transportation and communications. 
c)  One way governments attempt to reduce our vulnerability to terrorist incidents is by increasing security at airports and other public facilities. The U.S. government also works with other countries to limit the sources of support for terrorism. 
d)  The Federal Bureau of Investigation (FBI) categorizes terrorism in the United States as one of two types—domestic terrorism or international terrorism. 
1)  Domestic terrorism involves groups or individuals whose terrorist activities are directed at elements of our government or population without foreign direction. 
2)  International terrorism involves groups or individuals whose terrorist activities are foreign-based and/or directed by countries or groups outside the United States or whose activities transcend national boundaries. 
VI.  Biological and Chemical Weapons
Biological agents are infectious microbes or toxins used to produce illness or death in people, animals or plants. Biological agents can be dispersed as aerosols or airborne particles. Terrorists may use biological agents to contaminate food or water because they are extremely difficult to detect. Chemical agents kill or incapacitate people, destroy livestock or ravage crops. Some chemical agents are odorless and tasteless and are difficult to detect. They can have an immediate effect (a few seconds to a few minutes) or a delayed effect (several hours to several days). 
 

Disaster FactsTop Ten Major Disasters Ranked by FEMA Relief Costs*1989-1999Source: FEMA 
EVENT/YEAR FEMA FUNDING*
Northridge Earthquake (CA, 1994) $6.952 billion
Hurricane Georges (AL, FL, LA, MS, PR, USVI, 1998) $2.394 billion
Hurricane Andrew (FL, LA, 1992) $1.847 billion
Hurricane Hugo (NC, SC, PR, VI, 1989) $1.314 billion
Midwest Floods (IL,IA, KS, MN, MO, NE, ND, SD, WI, 1993) $1.144 billion
Hurricane Floyd (CT, DE, FL, ME, MD, NH, NJ, NY, NC, PA, SC, VT, VA, 1999) $880.4 million
Loma Prieta Earthquake (CA, 1989) $869.0 million
Red River Valley Floods (MN, ND, SD, 1997) $725.1 million
Hurricane Fran (MD, NC, PA, SC, VA, WVA, 1996) $630.2 million
Tropical Storm Alberto (AL, FL, GA, 1994) $542.8 million
*Amount obligated from the President’s Disaster Relief Fund for FEMA’s assistance programs, hazard mitigation grants, federal mission assignments, contractual services and administrative costs as of July 31, 2000. Figures do not include funding provided by other participating federal agencies, such as the disaster loan programs of the Small Business Administration and the Agriculture Department’s Farm Service Agency.