Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean, called the "Ring of Fire" because
of the preponderance of volcanic activity there as well. Most earthquakes occur at fault zones, where tectonic plates—
giant rock slabs that make up the Earth's upper layer—collide or slide against each other. These impacts are usually gradual
and unnoticeable on the surface; however, immense stress can build up between plates. When this stress is released quickly,
it sends massive vibrations, called seismic waves, often hundreds of miles through the rock and up to the surface.
Other quakes can occur far from faults zones when plates are stretched or squeezed.
Scientists assign a magnitude rating to earthquakes based on the strength and duration of their seismic waves.
A quake measuring 3 to 5 is considered minor or light; 5 to 7 is moderate to strong; 7 to 8 is major; and 8 or more is great.
On average, a magnitude 8 quake strikes somewhere every year and some 10,000 people die in earthquakes annually.
Collapsing buildings claim by far the majority of lives, but the destruction is often compounded by mud slides,
fires, floods, or tsunamis. Smaller temblors that usually occur in the days following a large earthquake can
complicate rescue efforts and cause further death and destruction.
Loss of life can be avoided through emergency planning, education, and the construction of buildings that
sway rather than break under the stress of an earthquake.
* Have an earthquake readiness plan.
* Consult a professional to learn how to make your home sturdier, such as bolting bookcases to wall studs,
installing strong latches on
cupboards, and strapping the water heater to wall studs.
* Locate a place in each room of the house that you can go to in case of an earthquake.
It should be a spot where nothing is likely to fall on you.
* Keep a supply of canned food, an up-to-date first aid kit, 3 gallons (11.4 liters) of water per person,
dust masks and goggles,and a working battery-operated radio and flashlights.
* Know how to turn off your gas and water mains.
If Shaking Begins
* Drop down; take cover under a desk or table and hold on.
* Stay indoors until the shaking stops and you're sure it's safe to exit.
* Stay away from bookcases or furniture that can fall on you.
* Stay away from windows. In a high-rise building, expect the fire alarms and sprinklers to go off during a quake.
* If you are in bed, hold on and stay there, protecting your head with a pillow.
* If you are outdoors, find a clear spot away from buildings, trees, and power lines. Drop to the ground.
* If you are in a car, slow down and drive to a clear place. Stay in the car until the shaking stops.
There are few places on Earth where people need not be concerned about flooding. Any place where rain falls is vulnerable, although rain is not the only impetus for flood.
A flood occurs when water overflows or inundates land that's normally dry. This can happen in a multitude of ways. Most common is when rivers or streams overflow their banks. Excessive rain, a ruptured dam or levee, rapid ice melting in the mountains, or even an unfortunately placed beaver dam can overwhelm a river and send it spreading over the adjacent land, called a floodplain. Coastal flooding occurs when a large storm or tsunami causes the sea to surge inland.
Most floods take hours or even days to develop, giving residents ample time to prepare or evacuate. Others generate quickly and with little warning. These flash floods can be extremely dangerous, instantly turning a babbling brook into a thundering wall of water and sweeping everything in its path downstream.
Disaster experts classify floods according to their likelihood of occurring in a given time period. A hundred-year flood, for example, is an extremely large, destructive event that would theoretically be expected to happen only once every century. But this is a theoretical number. In reality, this classification means there is a one-percent chance that such a flood could happen in any given year. Over recent decades, possibly due to global climate change, hundred-year floods have been occurring worldwide with frightening regularity.
Moving water has awesome destructive power. When a river overflows its banks or the sea drives inland, structures poorly equipped to withstand the water's strength are no match. Bridges, houses, trees, and cars can be picked up and carried off. The erosive force of moving water can drag dirt from under a building's foundation, causing it to crack and tumble.
In the United States, where flood mitigation and prediction is advanced, floods do about $6 billion worth of damage and kill about 140 people every year. A 2007 report by the Organization for Economic Cooperation and Development found that coastal flooding alone does some $3 trillion in damage worldwide. In China's Yellow River valley, where some of the world's worst floods have occurred, millions of people have perished in floods during the last century.
When floodwaters recede, affected areas are often blanketed in silt and mud. The water and landscape can be contaminated with hazardous materials, such as sharp debris, pesticides, fuel, and untreated sewage. Potentially dangerous mold blooms can quickly overwhelm water-soaked structures. Residents of flooded areas can be left without power and clean drinking water, leading to outbreaks of deadly waterborne diseases like typhoid, hepatitis A, and cholera.
But flooding, particularly in river floodplains, is as natural as rain and has been occurring for millions of years. Famously fertile floodplains like the Mississippi Valley in the American Midwest, the Nile River valley in Egypt,and the Tigris-Euphrates in the Middle East have supported agriculture for millennia because annual flooding has left millions of tons of nutrient-rich silt deposits behind.
Most flood destruction is attributable to humans' desire to live near picturesque coastlines and in river valleys. Aggravating the problem is a tendency for developers to backfill and build on wetlands that would otherwise act as natural flood buffers.
Many governments mandate that residents of flood-prone areas purchase flood insurance and build flood-resistant structures. Massive efforts to mitigate and redirect inevitable floods have resulted in some of the most ambitious engineering efforts ever seen, including New Orleans's extensive levee system and massive dikes and dams in the Netherlands. And highly advanced computer modeling now lets disaster authorities predict with amazing accuracy where floods will occur and how severe they're likely to be.
Before a Flood
* Avoid building in a floodplain.
* Construct barriers (levees, beams, floodwalls) to stop floodwater from entering your home.
* Seal walls in basements with waterproofing compounds to avoid seepage.
* If a flood is likely in your area, listen to the radio or television for information.
* Know the difference between a flood watch and a flood warning. A watch means flooding is possible.
A warning means flooding is occurring or will occur soon.
When a Flood is Imminent
* Be prepared! Pack a bag with important items in case you need to
evacuate. Don't forget to include needed medications.
* If advised to evacuate your home, do so immediately.
* If there is any possibility of a flash flood, move immediately to higher ground.
* If possible, bring in outdoor furniture and move essential items to an upper floor.
* Turn off utilities at the main switches or valves if instructed to do so. Disconnect electrical appliances.
During a Flood
* Do not walk through moving water. As little as 6 inches (15 centimeters)
of moving water can make you fall.
* If you have to walk in water, wherever possible, walk where the water is
not moving. Use a stick to check the firmness of the ground in front of you.
* Do not drive into flooded areas. If floodwaters rise around your car,
abandon the car and move to higher ground if you can do so safely.
* Do not touch electrical equipment if you are wet or standing in water.
After a Flood
* Listen for news reports to learn whether the community's water supply is safe to drink.
* Avoid floodwaters; water may be contaminated by oil, gasoline, or raw sewage.
Water may also be electrically charged from underground or downed power lines.
* Avoid moving water.
* Be aware of areas where floodwaters have receded. Roads may have
weakened and could collapse under the weight of a car.
* Stay away from downed power lines, and report them to the power company.
* Return home only when authorities indicate it is safe.
* Stay out of any building if it is surrounded by floodwaters.
* Service damaged septic tanks, cesspools, pits, and leaching systems as
soon as possible. Damaged sewage systems are serious health hazards.
* Clean and disinfect everything that got wet. Mud left from floodwater can
contain sewage and chemicals.
A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land.
These walls of water can cause widespread destruction when they crash ashore.
These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly it displaces the water above it and launches the rolling waves that will become a tsunami.
Most tsunamis, about 80 percent, happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where tectonic shifts make volcanoes and earthquakes common.
Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched,
as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean.
Tsunamis race across the sea at up to 500 miles (805 kilometers) an hour—about as fast as a jet airplane.
At that pace they can cross the entire expanse of the Pacific Ocean in less than a day.
And their long wavelengths mean they lose very little energy along the way.
In deep ocean, tsunami waves may appear only a foot or so high. But as they approach shoreline and
enter shallower water they slow down and begin to grow in energy and height.
The tops of the waves move faster than their bottoms do, which causes them to rise precipitously.
A tsunami’s trough, the low point beneath the wave’s crest, often reaches shore first. When it does,
it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors.
This retreating of sea water is an important warning sign of a tsunami, because the wave’s crest
and its enormous volume of water typically hit shore five minutes or so later. Recognizing this phenomenon can save lives.
A tsunami is usually composed of a series of waves, called a wave train, so its destructive force may
be compounded as successive waves reach shore. People experiencing a tsunami should remember
that the danger may not have passed with the first wave and should await official word that it is
safe to return to vulnerable locations.
Some tsunamis do not appear on shore as massive breaking waves but instead resemble a quickly
surging tide that inundates coastal areas.
The best defense against any tsunami is early warning that allows people to seek higher ground.
The Pacific Tsunami Warning System, a coalition of 26 nations headquartered in Hawaii,
maintains a web of seismic equipment and water level gauges to identify tsunamis at sea.
Similar systems are proposed to protect coastal areas worldwide.
* When in coastal areas, stay alert for tsunami warnings.
* Plan an evacuation route that leads to higher ground.
* Know the warning signs of a tsunami: rapidly rising or falling coastal
waters and rumblings of an offshore earthquake.
* Never stay near shore to watch a tsunami come in.
* A tsunami is a series of waves. Do not return to an affected coastal area
until authorities say it is safe.
Contrary to the common expression, lightning can and often does strike the same place twice,
especially tall buildings or exposed mountaintops. Cloud-to-ground lightning bolts are a common phenomenon—
about 100 strike Earth’s surface every single second—yet their power is extraordinary.
Each bolt can contain up to one billion volts of electricity.
This enormous electrical discharge is caused by an imbalance between positive and negative charges.
During a storm, colliding particles of rain, ice, or snow increase this imbalance and often negatively
charge the lower reaches of storm clouds. Objects on the ground, like steeples, trees, and the Earth itself,
become positively charged—creating an imbalance that nature seeks to remedy by passing current between the two charges.
A step-like series of negative charges, called a stepped leader, works its way incrementally
downward from the bottom of a storm cloud toward the Earth. Each of these segments is about 150 feet (46 meters) long.
When the lowermost step comes within 150 feet (46 meters) of a positively charged object it is met by a
climbing surge of positive electricity, called a streamer, which can rise up through a building, a tree, or even a person.
The process forms a channel through which electricity is transferred as lightning.
Some types of lightning, including the most common types, never leave the clouds but travel between
differently charged areas within or between clouds. Other rare forms can be sparked by extreme forest fires,
volcanic eruptions, and snowstorms. Ball lightning, a small, charged sphere that floats, glows,
and bounces along oblivious to the laws of gravity or physics, still puzzles scientists.
Lightning is extremely hot—a flash can heat the air around it to temperatures five times hotter than the sun’s surface.
This heat causes surrounding air to rapidly expand and vibrate, which creates the pealing thunder we hear a short
time after seeing a lightning flash.
Lightning is not only spectacular, it’s dangerous. About 2,000 people are killed worldwide by lightning each year.
Hundreds more survive strikes but suffer from a variety of lasting symptoms, including memory loss,
dizziness, weakness, numbness, and other life-altering ailments.
* If outside, seek refuge in a car or grounded building when lightning or thunder begins.
* If inside, avoid taking baths, or showers, and washing dishes. Also avoid using landline phones,
televisions, and other appliances that conduct electricity.
* Stay inside for 30 minutes after you last see lightning or hear thunder. People have been struck by
lightning from storms centered as far as 10 miles (16 kilometers) away.
* If caught outside away from a building or car, stay clear of water bodies and tall objects like trees.
Find a low spot or depression and crouch down as low as possible, but don't lie down on the ground.
Lightning can move in and along the ground surface, and many victims are struck not by bolts but by this current.
Volcanoes are awesome manifestations of the fiery power contained deep within the Earth.
These formations are essentially vents on the Earth's surface where molten rock, debris,
and gases from the planet's interior are emitted.
When thick magma and large amounts of gas build up under the surface, eruptions can be explosive,
expelling lava, rocks and ash into the air. Less gas and more viscous magma usually mean a less dramatic eruption,
often causing streams of lava to ooze from the vent.
The mountain-like mounds that we associate with volcanoes are what remain after the material
spewed during eruptions has collected and hardened around the vent. This can happen over a
period of weeks or many millions of years.
A large eruption can be extremely dangerous for people living near a volcano. Flows of searing lava,
which can reach 2,000 degrees Fahrenheit (1,250 degrees Celsius) or more, can be released,
burning everything in its path, including whole towns. Boulders of hardening lava can rain down on villages.
Mud flows from rapidly melting snow can strip mountains and valleys bare and bury towns.
Ash and toxic gases can cause lung damage and other problems, particularly for infants and the elderly.
Scientists estimate that more than 260,000 people have died in the past 300 years from volcanic eruptions and their aftermath.
Volcanoes tend to exist along the edges between tectonic plates, massive rock slabs that make up Earth's surface.
About 90 percent of all volcanoes exist within the Ring of Fire along the edges of the Pacific Ocean.
About 1,900 volcanoes on Earth are considered active, meaning they show some level of activity and are likely to explode again.
Many other volcanoes are dormant, showing no current signs of exploding but likely to become active at some point in the future.
Others are considered extinct.
• Stay away from active volcanoes.
• If you live near an active volcano, keep goggles and a mask in an emergency kit,
along with a flashlight and a working, battery-operated radio.
• Know your evacuation route. Keep gas in your car.
If a Volcano Erupts in Your Area
• Evacuate only as recommended by authorities to stay clear of lava, mud flows, and flying rocks and debris.
• Avoid river areas and low-lying regions.
• Before you leave the house, change into long-sleeved shirts and long pants and use goggles or eyeglasses, not contacts.
Wear an emergency mask or hold a damp cloth over your face.
• If you are not evacuating, close windows and doors and block chimneys and other vents, to prevent ash from coming into the house.
• Be aware that ash may put excess weight on your roof and need to be swept away. Wear protection during cleanups.
• Ash can damage engines and metal parts, so avoid driving. If you must drive, stay below 35 miles (56 kilometers) an hour.
While avalanches are sudden, the warning signs are almost always numerous before they let loose. Yet in 90 percent of avalanche incidents, the snow slides are triggered by the victim or someone in the victim's party. Avalanches kill more than 150 people worldwide each year. Most are snowmobilers, skiers, and snowboarders.
Many avalanches are small slides of dry powdery snow that move as a formless mass. These "sluffs" account for a tiny fraction of the death and destruction wrought by their bigger, more organized cousins. Disastrous avalanches occur when massive slabs of snow break loose from a mountainside and shatter like broken glass as they race downhill. These moving masses can reach speeds of 80 miles (130 kilometers) per hour within about five seconds. Victims caught in these events seldom escape. Avalanches are most common during and in the 24 hours right after a storm that dumps 12 inches (30 centimeters) or more of fresh snow. The quick pileup overloads the underlying snowpack, which causes a weak layer beneath the slab to fracture. The layers are an archive of winter weather: Big dumps, drought, rain, a hard freeze, and more snow. How the layers bond often determines how easily one will weaken and cause a slide.
Storminess, temperature, wind, slope steepness and orientation (the direction it faces), terrain, vegetation, and general snowpack conditions are all factors that influence whether and how a slope avalanches. Different combinations of these factors create low, moderate, considerable, and high avalanche hazards.
If caught in an avalanche, try to get off the slab. Not easy, in most instances. Skiers and snowboarders can head straight downhill to gather speed then veer left or right out of the slide path. Snowmobilers can punch the throttle to power out of harm's way. No escape? Reach for a tree. No tree? Swim hard. The human body is three times denser than avalanche debris and will sink quickly. As the slide slows, clear air space to breathe. Then punch a hand skyward.
Once the avalanche stops, it settles like concrete. Bodily movement is nearly impossible. Wait—and hope—for a rescue. Statistics show that 93 percent of avalanche victims survive if dug out within 15 minutes. Then the survival rates drop fast. After 45 minutes, only 20 to 30 percent of victims are alive. After two hours, very few people survive.
• Evaluate the avalanche hazard before attempting a rescue.
• Constantly evaluate avalanche of conditions.
• Areas with fresh accumulations of wind-driven snow are particularly vulnerable.
• Extremely steep slopes particularly in shaded areas near a ridge are also risky.
• Always travel with a partner. Descend risky areas one by one and watch for avalanche signs.
• Wear an avalanche rescue beacon that signals your location.
• Carry a small shovel and a long probe to locate a buried partner.
• Learn how to use the rescue equipment.
• Practice using the rescue equipment.
• Practice some more.
• If caught in a slide, try to get off the slab or grab a tree.
• If swept away, swim to the surface.
• Evaluate the avalanche hazard before attempting a rescue.
Hurricanes are giant, spiraling tropical storms that can pack wind speeds of over 160 miles (257 kilometers) an hour and unleash more than 2.4 trillion gallons (9 trillion liters) of rain a day. These same tropical storms are known as cyclones in the northern Indian Ocean and Bay of Bengal, and as typhoons in the western Pacific Ocean.
The Atlantic Ocean’s hurricane season peaks from mid-August to late October and averages five to six hurricanes per year.
Hurricanes begin as tropical disturbances in warm ocean waters with surface temperatures of at least 80 degrees Fahrenheit (26.5 degrees Celsius). These low pressure systems are fed by energy from the warm seas. If a storm achieves wind speeds of 38 miles (61 kilometers) an hour, it becomes known as a tropical depression. A tropical depression becomes a tropical storm, and is given a name, when its sustained wind speeds top 39 miles (63 kilometers) an hour. When a storm’s sustained wind speeds reach 74 miles (119 kilometers) an hour it becomes a hurricane and earns a category rating of 1 to 5 on the Saffir-Simpson scale.
Hurricanes are enormous heat engines that generate energy on a staggering scale. They draw heat from warm, moist ocean air and release it through condensation of water vapor in thunderstorms.
Hurricanes spin around a low-pressure center known as the “eye.” Sinking air makes this 20- to 30-mile-wide (32- to 48-kilometer-wide) area notoriously calm. But the eye is surrounded by a circular “eye wall” that hosts the storm’s strongest winds and rain.
These storms bring destruction ashore in many different ways. When a hurricane makes landfall it often produces a devastating storm surge that can reach 20 feet (6 meters) high and extend nearly 100 miles (161 kilometers). Ninety percent of all hurricane deaths result from storm surges.
A hurricane’s high winds are also destructive and may spawn tornadoes. Torrential rains cause further damage by spawning floods and landslides, which may occur many miles inland.
* Coastal residents should form evacuation plans before a warning is issued to identify a safe shelter and a route to get there.
* Stock up on emergency supplies including food, water, protective clothing, medications, batteries, flashlights,
important documents, road maps, and a full tank of gasoline.
Uncontrolled blazes fueled by weather, wind, and dry underbrush, wildfires can burn acres of land—and consume everything in their paths—in mere minutes.
On average, more than 100,000 wildfires, also called wildland fires or forest fires, clear 4 million to 5 million acres (1.6 million to 2 million hectares) of land in the U.S. every year. In recent years, wildfires have burned up to 9 million acres (3.6 million hectares) of land. A wildfire moves at speeds of up to 14 miles an hour (23 kilometers an hour), consuming everything—trees, brush, homes, even humans—in its path.
There are three conditions that need to be present in order for a wildfire to burn, which firefighters refer to as the fire triangle: fuel, oxygen, and a heat source. Fuel is any flammable material surrounding a fire, including trees, grasses, brush, even homes. The greater an area's fuel load, the more intense the fire. Air supplies the oxygen a fire needs to burn. Heat sources help spark the wildfire and bring fuel to temperatures hot enough to ignite. Lightning, burning campfires or cigarettes, hot winds, and even the sun can all provide sufficient heat to spark a wildfire.
Although four out of five wildfires are started by people, nature is usually more than happy to help fan the flames. Dry weather and drought convert green vegetation into bone-dry, flammable fuel; strong winds spread fire quickly over land; and warm temperatures encourage combustion. When these factors come together all that's needed is a spark—in the form of lightning, arson, a downed power line, or a burning campfire or cigarette—to ignite a blaze that could last for weeks and consume tens of thousands of acres.
These violent infernos occur around the world and in most of the 50 states, but they are most common in the U.S. West, where heat, drought, and frequent thunderstorms create perfect wildfire conditions. Montana, Idaho, Wyoming, Washington, Colorado, Oregon, and California experience some of the worst conflagrations in the U.S. In California wildfires are often made worse by the hot, dry Santa Ana winds, which can carry a spark for miles.
Firefighters fight wildfires by depriving them of one or more of the fire triangle fundamentals. Traditional methods include water dousing and spraying fire retardants to extinguish existing fires. Clearing vegetation to create firebreaks starves a fire of fuel and can help slow or contain it. Firefighters also fight wildfires by deliberately starting fires in a process called controlled burning. These prescribed fires remove undergrowth, brush, and ground litter from a forest, depriving a wildfire of fuel.
Although often harmful and destructive to humans, naturally occurring wildfires play an integral role in nature. They return nutrients to the soil by burning dead or decaying matter. They also act as a disinfectant, removing disease-ridden plants and harmful insects from a forest ecosystem. And by burning through thick canopies and brushy undergrowth, wildfires allow sunlight to reach the forest floor, enabling a new generation of seedlings to grow.
Tornadoes are vertical funnels of rapidly spinning air. Their winds may top 250 miles (400 kilometers) an hour and can clear-cut a pathway a mile (1.6 kilometers) wide and 50 miles (80 kilometers) long.
Twisters are born in thunderstorms and are often accompanied by hail. Giant, persistent thunderstorms called supercells spawn the most destructive tornadoes.
These violent storms occur around the world, but the United States is a major hotspot with about a thousand tornadoes every year. "Tornado Alley," a region that includes eastern South Dakota, Nebraska, Kansas, Oklahoma, northern Texas, and eastern Colorado, is home to the most powerful and destructive of these storms. U.S. tornadoes cause 80 deaths and more than 1,500 injuries per year.
A tornado forms when changes in wind speed and direction create a horizontal spinning effect within a storm cell. This effect is then tipped vertical by rising air moving up through the thunderclouds.
The meteorological factors that drive tornadoes make them more likely at some times than at others. They occur more often in late afternoon, when thunderstorms are common, and are more prevalent in spring and summer. However, tornadoes can and do form at any time of the day and year.
Tornadoes' distinctive funnel clouds are actually transparent. They become visible when water droplets pulled from a storm's moist air condense or when dust and debris are taken up. Funnels typically grow about 660 feet (200 meters) wide.
Tornadoes move at speeds of about 10 to 20 miles (16 to 32 kilometers) per hour, although they've been clocked in bursts up to 70 miles (113 kilometers) per hour. Most don't get very far though. They rarely travel more than about six miles (ten kilometers) in their short lifetimes.
Tornadoes are classified as weak, strong, or violent storms. Violent tornadoes comprise only about two percent of all tornadoes, but they cause 70 percent of all tornado deaths and may last an hour or more.
People, cars, and even buildings may be hurled aloft by tornado-force winds—or simply blown away. Most injuries and deaths are caused by flying debris.
Tornado forecasters can't provide the same kind of warning that hurricane watchers can, but they can do enough to save lives. Today the average warning time for a tornado alert is 13 minutes. Tornadoes can also be identified by warning signs that include a dark, greenish sky, large hail, and a powerful train-like roar.
• Prepare for tornadoes by gathering emergency supplies including food, water, medications, batteries, flashlights,
important documents, road maps, and a full tank of gasoline.
• When a tornado approaches, anyone in its path should take shelter indoors—preferably in a basement or an interior first-floor room or hallway.
• Avoid windows and seek additional protection by getting underneath large, solid pieces of furniture.
• Avoid automobiles and mobile homes which provide almost no protection from tornadoes.
• Those caught outside should lie flat in a depression or on other low ground and wait for the storm to pass.
* As a storm unfolds, evacuees should listen to local authorities on radio or television.
Evacuation routes often close as a storm develops.
* Dedicated professionals and improved technology have made hurricane forecasting more accurate than ever before—
but it’s far from precise.
* If forced to weather a storm, get inside the most secure building possible and stay away from windows.
* Remember that a lull often signifies the storm’s eye—not its end. Anyone riding out a hurricane should wait for
authorities to announce that the danger has passed.